that of Lepidoptera, viz. a mummy-like object, or pupa obtecta, in which
there is a crisp outer shell, formed in part by the adherent cases of the
appendages of the future imago. This condition, with a few exceptions to be
subsequently noticed, obtains in the Nemocera and Brachycera. It is
exhibited in various degrees of perfection, being most complete in
Tipulidae; in other forms the shell is softer and the appendages more
protuberant. The second kind of pupa is found in the Cyclorrhaphous flies;
it has externally no marks except some faint circular rings and,
frequently, a pair of projections from near one extremity of the body;
occasionally there is a single prominence at the other extremity of the
body. This condition is due to the fact that the larva does not escape from
the skin at the last ecdysis, but merely shrinks within it, so that the
larval skin, itself contracted and altered by an excretion of chitin,
remains and forms a perfect protection to the included organism. This kind
of pupa looks like a seed, and is well exemplified by the common Blow-fly.
The capacity for entering on such a condition is evidently correlative with
the absence of a larval head. The metamorphosis in this curious little
barrel goes on in a different manner to what it does in the pupa
{452}obtecta. A good name for the whole structure of this instar has not
been found. Older authors called it "pupa coarctata," or "nympha inclusa";
Brauer speaks of it as a "compound pupa"; ordinarily in our language it is
called a "puparium," a term which is more applicable to the case alone.
In species having a pupa obtecta the larval skin is cast after the chief
processes of the external metamorphosis have occurred, and then an
exudation of chitin hardens the general surface. In the "compound pupa" of
the Blow-fly there is for a considerable period no formed pupa at all, but
merely a shell or case containing the results of histolysis and the centres
for regeneration of new organs; the chitin-exudation to the exterior of the
larval skin occurs in the early part of the series of metamorphic changes,
and the organism breaks down to a cream within the shell thus formed, and
then gradually assumes therein the condition of a soft, nymphoid pupa. The
exceptional conditions previously referred to as exhibited by a few forms
are certain cases in which a more or less perfect pupa obtecta is found
within the last larval skin, as is the case in _Stratiomys_. Another highly
remarkable condition exists in the Hessian fly, and a few other
Cecidomyiids, where the Insect apparently makes an exudation which it uses
as a covering case, independent of the larval skin; this latter being
subsequently shed inside the case, so that this condition of coarctate pupa
differs from that we have described as existing in Cyclorrhaphous flies,
although the two are superficially similar. In the Pupipara the larval
stage is passed in the body of the mother, which produces a succession of
young, nourished one at a time by the secretion of glands; this young is
born as a full-grown larva that becomes at once a pupa.
METAMORPHOSIS.—As it is in Diptera that the phenomena of
Insect-metamorphosis have reached their highest development we endeavoured
to give some idea of their nature in the previous volume, therefore we need
give only a brief sketch of the chief features of Dipterous metamorphosis.
The Blow-fly undergoes a rapid embryonic development, the later stages of
which are, on the whole, of a retrogressive nature. On the emergence of the
young maggot it feeds up rapidly, the rapidity varying greatly according to
circumstances, and then when full-grown rests. While resting, a process of
internal liquefaction, called histolysis, is going on, and the maggot
contracts and exudes an excretion {453}that hardens its skin. At the time
this hard skin has become complete, or soon after, the maggot inside has
dissolved into a cream contained in a sac inside the shell; this cream
becomes reconstituted into a fly by a gradual process of growth and
development of certain minute portions of the body—the imaginal discs or
folds, the histoblasts and neuroblasts that were exempt from the histolytic
process: in the early stages of the reconstitution the general structure
is, of course, altogether vague, and this condition—purely one of
transition—is called the pronymph; the nymph becomes gradually developed:
it corresponds vaguely with the pupa obtecta of the early groups of
Diptera, but is soft like the pupa of Hymenoptera. This nymph gradually
develops into the fly itself, the external parts being first completed and
the internal organs elaborated subsequently. The sexual organs do not
undergo metamorphosis like other internal organs, there being a gradual
(though irregular or interrupted) growth of them in the young larva, till
they are completed some time after the emergence of the perfect fly. The
processes in the Blow-fly have been studied by numerous able histologists
of various nationalities, and have recently been described by Lowne in our
own language.[361] Comparatively little has been done in studying the
corresponding phenomena in other Diptera. Weismann has investigated the
development of _Corethra_, and Miall that of _Chironomus_. These two flies
belong to a division of Diptera different from that which includes the
Blow-fly, and they display a condition of the metamorphic processes allied
to what occurs in Lepidoptera, as well as to that which takes place in the
Blow-fly. Imaginal folds are formed, but they only appear much later in the
life, and they are much less distant from the positions they will, when
developed, occupy in the imago. In _Chironomus_, according to Miall, the
imaginal folds only appear in the last larval instar, but they grow with
such rapidity that the legs and wings of the future fly can be
distinguished in the larva, even before pupation; thus when the activity of
the larva ceases but little change is required to complete the obtected
pupa. In the Blow-fly some of the imaginal folds have been {454}traced back
to the embryo; how many centres for the new growth there may be is
uncertain, for though there are upwards of sixty for the outer body, the
number of regenerative centres for the internal organs is not ascertained.
The peculiar central nervous mass, mentioned in our remarks on the larva,
consists of two kinds of tissue mixed together in a complex manner; one of
these kinds is functionally active during the larval life and at the
metamorphosis undergoes histolysis, while the other, or embryonic, portion
develops into the nervous system of the fly.
It forms no part of our task to deal with general subjects, but we may be
pardoned for calling attention to the bearing the metamorphosis of the
higher Diptera has on our ideas of heredity in Insects. The fly bears no
resemblance whatever to the larva, and is only obtained by the organic
destruction of the latter, which occurs before the perfection of the sexual
organs takes place, and yet the fly reproduces itself only secondarily, but
primarily gives rise to the totally different larva. It is supposed that
the larval structures have been gradually acquired, and yet they are
transmitted with the utmost faithfulness by the totally different fly. We
can only conclude that that which is bequeathed in each species is the
early state of a particular process of development from which the
subsequent stages follow necessarily if the developing organism be placed
in conditions having on it influences like to those that influenced the
ancestors.
CLASSIFICATION.—The classification of Diptera is as yet very imperfect.
Formerly they were divided into two great groups, Nemocera and Brachycera,
according to the structure of the antennae, as previously mentioned. This
division has been abandoned, and the term Brachycera is now applied to only
a small part of the old section that bore the name. The primary division
usually adopted at present is into Orthorrhapha and Cyclorrhapha. The
characters of these two groups are based on the nature of the
metamorphosis, and have been gradually elaborated by Brauer in various
memoirs.[362] The Orthorrhapha includes the forms with obtected pupae, the
Cyclorrhapha those with a nymph-compound, as previously described. This
distinction is of great importance, but unfortunately it is difficult to
apply to the fly itself; the only character that can be used in
{455}connection with the imago is the existence of a suture over the
insertion of the antennae in a portion, but not all, of the
Cyclorrhapha.[363] The next set of divisions used by Brauer divides the
Order into four sections, viz. 1. Orthorrhapha Nematocera, 2. O.
Brachycera, 3. Cyclorrhapha Aschiza, 4. C. Schizophora. As these four
groups are recognised more readily than the two major groups the student
will do well at first to disregard the primary division and consider the
Diptera as divisible into four great groups. To these four divisions we,
however, add temporarily a fifth, viz. Pupipara. This is included by Brauer
in Schizophora, but it appears to be really an unnatural complex, and had
better be kept separate till it has been entirely reconsidered. These great
sections may be thus summarised:—
Series 1. _Orthorrhapha Nemocera._—Antennae with more than 6 segments,
not terminated by an arista; with the segments of the flagellum more or
less similar to one another. Palpi slender and flexible, four- or
five-jointed.[364]
Series 2. _Orthorrhapha Brachycera._—Antennae variable, but never truly
Nemocerous nor like those of Cyclorrhapha; when an arista is present it
is usually placed terminally, not superiorly; when an arista is not
present the flagellum terminates as an appendage consisting of a variable
number of indistinctly separated segments; thus the flagellum is not
composed of similar joints; [rarely are the antennae as many as
seven-jointed]. Palpi only one- or two-jointed.[365] Around the insertion
of the antennae there is no definite arched suture enclosing a small
depressed space. The nervuration of the wings is usually more complex
than in any of the other divisions.
Series 3. _Cyclorrhapha Aschiza._—Antennae composed of not more than
three joints and an arista; the latter is not terminal. Front of head
without definite arched suture over the antennae, but frequently with a
minute area of different colour or texture there. This group consists of
the great family Syrphidae, and of four small families, viz. Conopidae,
Pipunculidae, Phoridae, and Platypezidae. The section is supposed to be
justified by its being Cyclorrhaphous in pupation, and by the members not
possessing a ptilinum (or having no trace of one when quite mature). The
Syrphidae are doubtless {456}a natural group, but the association with
them of the other families mentioned is a mere temporary device. The
greatest difficulty is experienced in deciding on a position for
Phoridae, as to which scarcely any two authorities are agreed.
Series 4. _Cyclorrhapha Schizophora_, or Eumyiid flies. The antennae
consist of three joints and an arista. In the Calyptratae the frontal
suture, or fold over the antennae, is well marked and extends downwards
along each side of the face, leaving a distinct lunule over the antennae.
In the Acalyptrate Muscids the form of the head and of the antennae vary
much and are less characteristic, but the wings differ from those of
Brachycera by their much less complex nervuration.
Series 5. _Pupipara._ These are flies of abnormal habits, and only found
in connection with living Vertebrates, of which they suck the blood (one
species, _Braula caeca_, lives on bees). Many are wingless, or have wings
reduced in size. The young are produced alive, full grown, but having
still to undergo a metamorphosis. This group consists of a small number
of flies of which some are amongst the most aberrant known. This is
specially the case with the Nycteribiidae. This Section will probably be
greatly modified, as it is far from being a natural assemblage.[366]
The Sub-Order _Aphaniptera_, or Fleas, considered a distinct Order by
many entomologists, may for the present be placed as a part of Diptera.
It must be admitted that these sections are far from satisfactory. Brauer
divides them into Tribes, based on the nature of the larvae, but these
tribes are even more unsatisfactory than the sections, hosts of species
being entirely unknown in the larval state, and many of those that are
known having been very inadequately studied. We must admit that the
classification of Diptera has at present advanced but little beyond the
stage of arranging them in natural families capable of exact definition. We
may, however, draw attention to the attempt that is being made by Osten
Sacken to remodel the classification of the Nemocera and Brachycera by the
combination of families into super-families.[367] He proposes to divide the
Nemocera into two super-families: 1. Nemocera Vera, including all the
families from Cecidomyiidae to Tipulidae; 2. Nemocera Anomala, consisting
of the small families Bibionidae, Simuliidae, Blepharoceridae, Rhyphidae
and Orphnephilidae.
For Orthorrhapha Brachycera he adopts the following {457}arrangement: 1.
Super-family Eremochaeta, for Stratiomyidae, Tabanidae, Acanthomeridae and
Leptidae; 2. Tromoptera, for Nemestrinidae, Acroceridae, Bombyliidae,
Therevidae, and Scenopinidae; 3. Energopoda, for Asilidae, Dolichopidae,
Empidae and Lonchopteridae, Phoridae being included with doubt; 4. Mydaidae
remains isolated.
This classification is based on the relations of the eyes and bristles of
the upper surface, and on the powers of locomotion, aërial or terrestrial.
At present it is not sufficiently precise to be of use to any but the very
advanced student.
BLOOD-SUCKING DIPTERA.—The habit of blood-sucking from Vertebrates is,
among Insects, of course confined to those with suctorial mouth, and is
exhibited by various Diptera. It is, however, indulged in by but a small
number of species, and these do not belong to any special division of the
Order. It is remarkable that as a rule the habit is confined to the female
sex, and that a large proportion of the species have aquatic larvae. This
subject has many points of interest, but does not appear to have yet
received the attention it merits. We give below a brief summary of the
facts as to blood-sucking Diptera.
Series I. Nemocera.—In this section the habit occurs in no less than five
families, viz.:
Blepharoceridae. _Curupira_; in the female only; larva aquatic.
Culicidae. _Culex_, Mosquitoes; in the female only; other genera, with
one or two exceptions, do not suck blood; larvae aquatic.
Chironomidae. _Ceratopogon_, Midge; in the female only; exceptional
even in the genus, though the habit is said to exist in one or two less
known, allied genera; larval habits not certain; often aquatic; in _C.
bipunctatus_ the larva lives under moist bark.
Psychodidae. _Phlebotomus_: in the female only (?); quite exceptional
in the family; larva aquatic or in liquid filth.
Simuliidae. _Simulium_, sand-flies; general in the family (?), which,
however, is a very small one; larva aquatic, food probably mixed
vegetable and animal microscopic organisms.
Series II. Brachycera. Tabanidae. Gad-flies: apparently general in the
females of this family; the habits of the exotic forms but little known;
in the larval state, scarcely at all known; some are aquatic.
{458}Series IV. Cyclorrhapha Schizophora: _Stomoxys_, _Haematobia_; both
sexes (?); larvae in dung. [The Tse-tse flies, _Glossina_, are placed in
this family, though their mode of parturition is that of the next
section].
Series V. Pupipara. The habit of blood-sucking is probably common to all
the group and to both sexes. The flies, with one exception, frequent
Vertebrates; in many cases living entirely on their bodies, and
apparently imbibing much blood; the larvae are nourished inside the
flies, not on the imbibed blood, but on a milky secretion from the
mother.
Sub-Order Aphaniptera. Fleas. The habit of blood-sucking is common to all
the members and to both sexes. The larvae live on dried animal matter.
FOSSIL DIPTERA.—A considerable variety of forms have been found in amber,
and many in the tertiary beds; very few members of the Cyclorrhaphous
Sections are, however, among them; the Tipulidae, on the other hand, are
richly represented. In the Mesozoic epoch the Order is found as early as
the Lias, the forms being exclusively Orthorrhaphous, both Nemocera and
Brachycera being represented. All are referred to existing families.
Nothing has been found tending to connect the Diptera with other Orders. No
Palaeozoic Diptera are known.
SERIES 1. ORTHORRHAPHA NEMOCERA
FAM. 1. CECIDOMYIIDAE.—_An extensive family of very minute and fragile
flies, the wings of which have very few nervures; the antennae are rather
long, and are furnished with whorls of hair._ In the case of some species
the antennae are beautiful objects; in _Xylodiplosis_ some of the hairs
have no free extremities, but form loops (Fig. 220). In the males of
certain species the joints appear to be double, each one consisting of a
neck and a body. Although comparatively little is known as to the flies
themselves, yet these Insects are of importance on account of their
preparatory stages. The larvae have very diverse habits; the majority live
in plants and form galls, or produce deformations of the leaves, flowers,
stems, buds, or roots in a great variety of ways; others live under bark or
in animal matter; some are predaceous, killing Aphidae or Acari, and even
other Cecidomyiids.
{459}[Illustration: Fig. 219—_Cecidomyia_ (_Diplosis_) _buxi_. Britain. A,
Larva, magnified; B, pupa; C, imago; D, portion of antenna. (After
Laboulbène.)]
[Illustration: Fig. 220—One segment of antenna of _Xylodiplosis_ sp.; _a_,
Tip of one segment; _b_, base of another. (After Janet.)]
The North American _Diplosis resinicola_ lives in the resin exuded as the
results of the attacks of a caterpillar. The larva burrows in the
semi-liquid resin, and, according to Osten Sacken,[368] is probably
amphipneustic. Cecidomyiid larvae are short maggots, narrowed at the two
ends, with a very small head, and between this and the first thoracic
segment (this bears a stigma), a small supplementary segment; the total
number of segments is thirteen, besides the head; there are eight pairs of
stigmata on the posterior part of the body. Brauer defines the Cecidomyiid
larva thus, "peripneustic, with nine pairs of stigmata, the first on the
second segment behind the head; two to nine on fifth to twelfth segments;
body as a whole fourteen-segmented without a fully-formed head." The most
remarkable peculiarity of Cecidomyiid larvae is that those of many species
possess a peculiar organ—called breast-bone, sternal spatula, or
anchor-process—projecting from the back of the lower face of the
prothoracic segment. The use of so peculiar a structure has been much
discussed. According to Giard,[369] in addition to the part {460}that
protrudes externally, as shown in Fig. 219, A, there is a longer portion
concealed, forming a sort of handle, having muscles attached to it. Some of
these larvae have the power of executing leaps, and he states that such
larvae are provided on the terminal segment with a pair of corneous
papillae; bending itself almost into a circle, the larva hooks together the
breast-bone and the papillae, and when this connection is broken the spring
occurs. This faculty is only possessed by a few species, and it is probable
that in other cases the spatula is used as a means for changing the
position or as a perforator. Some of the larvae possess false feet on
certain of the segments. Williston says they probably do not moult. In the
pupal instar (Fig. 219, B), the Cecidomyiid greatly resembles a minute
Lepidopterous pupa. The Hessian fly, _Cecidomyia destructor_, is frequently
extremely injurious to crops of cereals, and in some parts of the world
commits serious depredation. The larva is lodged at the point where a leaf
enwraps the stem; it produces a weakness of the stem, which consequently
bends. This Insect and _C. tritici_ (the larva of which attacks the flowers
of wheat) pupate in a very curious manner: they form little compact cases
like flax-seeds; these have been supposed to be a form of pupa similar to
what occurs in the Blow-fly; but there are important distinctions. The
larva, when about to undergo its change, exudes a substance from its skin,
and this makes the flax-seed; the larval skin itself does not form part of
this curious kind of cocoon, for it may be found, as well as the pupa, in
the interior of the "flax-seed." Other Cecidomyiids form cocoons of a more
ordinary kind; one species, described by Perris as living on _Pinus
maritima_, has the very remarkable faculty of surrounding itself, by some
means, with a cocoon of resin. Walsh describes the cocoon-forming process
of certain Cecidomyiids as one of exudation and inflation; Williston as
somewhat of the nature of crystallisation. Some Cecidomyiids are said to
possess, in common with certain other Diptera, the unusual number of five
Malpighian tubes; and Giard says that in the larva there is only a pair of
these tubes, and that their extremities are united so as to form a single
tube, which is twisted into an elegant double loop.
Thirty years or more ago the Russian naturalist, Wagner, made the very
remarkable discovery that the larva of a Cecidomyiid produces young; and it
has since been found by Meinert and {461}others that this kind of
paedogenesis occurs in several species of the genera _Miastor_ and
_Oligarces_. The details are briefly as follows:—A female fly lays a few,
very large, eggs, out of each of which comes a larva, that does not go on
to the perfect state, but produces in its interior young larvae that, after
consuming the interior of the body of the parent larva, escape by making a
hole in the skin, and thereafter subsist externally in a natural manner.
This larval reproduction may be continued for several generations, through
autumn, winter, and spring till the following summer, when a generation of
the larvae goes on to pupation and the mature, sexually perfect fly
appears. Much discussion has taken place as to the mode of origination of
the larvae; Carus and others thought they were produced from the
rudimental, or immature ovaries of the parent larva. Meinert, who has made
a special study of the subject,[370] finds, however, that this is not the
case; in the reproducing larva of the autumn there is no ovary at all; in
the reproducing larvae of the spring-time rudimentary ovaries or testes, as
the case may be, exist; the young are not, however, produced from these,
but from germs in close connection with the fat-body. In the larvae that go
on to metamorphosis the ovaries continue their natural development. It
would thus appear that the fat-body has, like the leaf of a _Begonia_,
under certain circumstances, the power, usually limited to the ovaries, of
producing complete and perfect individuals.
Owing to the minute size and excessive fragility of the Gall-midge flies it
is extremely difficult to form a collection of them; and as the larvae are
also very difficult of preservation, nearly every species must have its
life-history worked out as a special study before the name of the species
can be ascertained. Notwithstanding the arduous nature of the subject it
is, however, a favourite one with entomologists. The number of described
and named forms cannot be very far short of 1000, and each year sees some
20 or 30 species added to the list. The number of undescribed forms is
doubtless very large. The literature of the subject is extensive and of the
most scattered and fragmentary character.
The Cecidomyiidae have but little relation to other Nemocera, and are
sometimes called Oligoneura, on account of the reduced number of
wing-nervures. Their larvae are of a peculiar type {462}that does not agree
with the larvae of the allied families having well-marked heads (and
therefore called Eucephala), nor with the acephalous maggots of Eumyiidae.
FAM. 2. MYCETOPHILIDAE.—_These small flies are much less delicate creatures
than the Cecidomyiidae, and have more nervures in the wings; they possess
ocelli, and frequently have the coxae elongated, and in some cases the legs
adorned with complex arrangements of spines: their antennae have not whorls
of hair._ Although very much neglected there are probably between 700 and
1000 species known; owing to many of their larvae living in fungoid matter
the flies are called Fungus-gnats. We have more than 100 species in
Britain. _Epidapus_ is remarkable, inasmuch as the female is entirely
destitute of wings and halteres, while the male has the halteres developed
but the wings of very reduced size. _E. scabiei_ is an excessively minute
fly, smaller than a common flea, and its larva is said to be very injurious
to stored potatoes. The larvae of Mycetophilidae are usually very elongate,
worm-like maggots, but have a distinct, small head; they are peripneustic,
having, according to Osten Sacken, nine pairs of spiracles, one pair
prothoracic, the others on the first eight abdominal segments. They are
usually worm-like, and sometimes seem to consist of twenty segments. Some
of them have the faculty of constructing a true cocoon by some sort of
spinning process, and a few make earthen cases for the purpose of pupation.
The pupae themselves are free, the larval skin having been shed. The
Mycetophilidae are by no means completely fungivorous, for many live in
decaying vegetable, some even in animal, matter.
[Illustration: Fig. 221—_Mycetobia pallipes._ Britain. A, Larva; B, pupa;
C, imago. (After Dufour.)]
The habits of many of the larvae are very peculiar, owing to their spinning
or exuding a mucus, that reminds one of snail-slime; they are frequently
gregarious, and some of them have likewise, as we shall subsequently
mention, migratory habits. Perris has described the very curious manner in
which _Sciophila {463}unimaculata_ forms its slimy tracks;[371] it
stretches its head to one side, fixes the tip of a drop of the viscous
matter from its mouth to the surface of the substance over which it is to
progress, bends its head under itself so as to affix the matter to the
lower face of its own body; then stretches its head to the other side and
repeats the operation, thus forming a track on which it glides, or perhaps,
as the mucus completely envelops its body, we should rather call it a
tunnel through which the maggot slips along. According to the description
of Hudson[372] the so-called New Zealand Glow-worm is the larva of
_Boletophila luminosa_; it forms webs in dark ravines, along which it
glides, giving a considerable amount of light from the peculiarly formed
terminal segment of the body. This larva is figured as consisting of about
twenty segments. The pupa is provided with a very long, curiously-branched
dorsal structure: the fly issuing from the pupa is strongly luminous,
though no use can be discovered for the property either in it or in the
larva. The larva of the Australian _Ceroplatus mastersi_ is also luminous.
Another very exceptional larva is that of _Epicypta scatophora_; it is of
short, thick form, like Cecidomyiid larvae, and has a very remarkable
structure of the dorsal parts of the body; by means of this its excrement,
which is of a peculiar nature, is spread out and forms a case for
enveloping and sheltering the larva. Ultimately the larval case is
converted into a cocoon for pupation. This larva is so different from that
of other Mycetophilidae, that Perris was at first unable to believe that
the fly he reared really came from this unusually formed larva. The larva
of _Mycetobia pallipes_ (Fig. 221) offers a still more remarkable
phenomenon, inasmuch as it is amphipneustic instead of peripneustic (that
is to say, it has a pair of stigmata at the termination of the body and a
pair on the first thoracic segment instead of the lateral series of pairs
we have described as normal in Mycetophilidae). This larva lives in company
with the amphipneustic larva of _Rhyphus_, a fly of quite another family,
and the _Mycetobia_ larva so closely resembles that of the _Rhyphus_, that
it is difficult to distinguish the two. This anomalous larva gives rise,
like the exceptional larva of _Epicypta_, to an ordinary Mycetophilid
fly.[373]
{464}But the most remarkable of all the Mycetophilid larvae are those of
certain species of _Sciara_, that migrate in columns, called by the
Germans, Heerwurm. The larva of _Sciara militaris_ lives under layers of
decomposing leaves in forests, and under certain circumstances, migrates,
sometimes perhaps in search of a fresh supply of food, though in some cases
it is said this cannot be the reason. Millions of the larvae accumulate and
form themselves by the aid of their viscous mucus into great strings or
ribbons, and then glide along like serpents: these aggregates are said to
be sometimes forty to a hundred feet long, five or six inches wide, and an
inch in depth. It is said that if the two ends of one of these processions
be brought into contact, they become joined, and the monstrous ring may
writhe for many hours before it can again disengage itself and assume a
columnar form. These processional maggots are met with in Northern Europe
and the United States, and there is now an extensive literature about
them.[374] Though they sometimes consist of almost incredible numbers of
individuals, yet it appears that in the Carpathian mountains the
assemblages are usually much smaller, being from four to twenty inches
long. A species of _Sciara_ is the "Yellow-fever fly" of the Southern
United States. It appears that it has several times appeared in unusual
numbers and in unwonted localities at the same time as the dreaded disease,
with which it is popularly supposed to have some connection.
FAM. 3. BLEPHAROCERIDAE.[375]—_Wings with no discal cell, but with a
secondary set of crease-like lines._ The flies composing this small family
are very little known, and appear to be obscure Insects with somewhat the
appearance of Empidae, though with strongly iridescent wings; they execute
aerial dances, after the manner of midges, and are found in Europe (the
Pyrenees, Alps and Harz mountains) as well as in North and South America.
Their larvae are amongst the most remarkable of Insect forms; indeed, no
entomologist recognises them as belonging to a Hexapod Insect when he makes
a first {465}acquaintance with them. The larva of _Curupira_ (Fig. 222)
lives in rapid streams in Brazil, fixed by its suckers to stones or rocks.
It consists only of six or seven divisions, with projecting side-lobes; the
usual segmentation not being visible. There are small tracheal gills near
the suckers, and peculiar scale-like organs are placed about the edges of
the lobes. Müller considers that the first lobe is "cephalothorax,"
corresponding to head, thorax and first abdominal segment of other larvae,
the next four lobes he considers to correspond each to an abdominal
segment, and the terminal mass to four segments. He also says that certain
minute points existing on the surface, connected with the tracheal system
by minute strings, represent nine pairs of spiracles. These larvae and
their pupae can apparently live only a short time after being taken out of
the highly aërated water in which they exist, but Müller succeeded in
rearing several flies from a number of larvae and pupae that he collected,
and, believing them to be all one species, he announced that the females
exhibited a highly developed dimorphism, some of them being blood-suckers,
others honey-suckers. It is however, more probable that these specimens
belonged to two or three distinct species or even genera. This point
remains to be cleared up. The larva we have figured is called by Müller
_Paltostoma torrentium_. It is certain, however, that the Brazilian Insect
does not belong to the genus _Paltostoma_, and it will no doubt bear the
name used by Osten Sacken, viz. _Curupira_.
[Illustration: Fig. 222—Under surface of the larva of _Curupira_
(_Paltostoma_) _torrentium_, showing the suckers along the middle of the
body, much magnified. Brazil. (After Fritz Müller.)]
The metamorphoses of the European _Liponeura brevirostris_ have been
partially examined by Dewitz, who found the Insects in the valley of the
Ocker in September.[376] He does not consider the "cephalothorax" to
include an abdominal segment; and he found that two little, horn-like
projections from the thorax of the {466}pupa are really each four-leaved.
The pupa is formed within the larval skin, but the latter is subsequently
cast so that the pupa is exposed; its dorsal region is horny, but the under
surface, by which it clings firmly to the stones of the rapid brook, is
white and scarcely chitinised, and Dewitz considers that the chitinous
exudation from this part is used as a means of fastening the pupa to the
stones. Blepharoceridae possess, in common with _Culex_, _Psychoda_ and
_Ptychoptera_, the peculiar number of five Malpighian tubes, and it has
been proposed by Müller to form these Insects into a group called
Pentanephria.
FAM. 4. CULICIDAE (_Mosquitoes_, _Gnats_).—_Antennae with whorls of hair or
plumes, which may be very dense and long in the male, though scanty in the
female; head with a long, projecting proboscis._ Although there are few
Insects more often referred to in general literature than Mosquitoes, yet
the ideas in vogue about them are of the vaguest character. The following
are the chief points to be borne in mind as to the prevalence of
Mosquitoes:—The gently humming Gnat that settles on us in our apartments,
and then bites us, is a Mosquito; there are a large number of species of
Mosquitoes; in some countries many in one locality; in Britain we have ten
or a dozen; notwithstanding the multiplicity of species, certain Mosquitoes
are very widely diffused; the larvae are all aquatic, and specially
frequent stagnant or quiet pools; they are probably diffused by means of
the water in ships, it being known that Mosquitoes were introduced for the
first time to the Hawaiian Islands by a sailing vessel about the year 1828.
Hence it is impossible to say what species the Mosquitoes of a given
locality may be without a critical examination. No satisfactory work on the
Mosquitoes of the world exists. Urich states that he is acquainted with at
least ten species in Trinidad. The species common in our apartments in
Central and Southern England is _Culex pipiens_, Linn., and this species is
very widely distributed, being indeed one of the troublesome Mosquitoes of
East India. The term Mosquito is a Spanish or Portuguese diminutive of
Mosca. It is applied to a variety of small flies of other families than
Culicidae, but should be restricted to these latter. The irritation
occasioned by the bites of Mosquitoes varies according to several
circumstances, viz. the condition of the biter, the condition or
constitution of the bitten, and also the species of Mosquito. Réaumur and
{467}others believed that some irritating fluid is injected by the Mosquito
when it bites. But why should it want to irritate as well as to bite?
Macloskie, considering that the Mosquito is really a feeder on
plant-substances, suggests that the fluid injected may be for the purpose
of preventing coagulation of the plant-juices during the process of
suction. It is a rule that only the female Mosquito bites, the male being
an inoffensive creature, and provided with less effectual mouth-organs; it
has, however, been stated by various authors that male Mosquitoes do
occasionally bite. It is difficult to understand the blood-sucking
propensities of these Insects; we have already stated that it is only the
females that suck blood. There is reason to suppose that it is an acquired
habit; and it would appear that the food so obtained is not essential to
their existence. It has indeed been asserted that the act is frequently
attended with fatal consequences to the individual that does it. The proper
method of mitigating their nuisance is to examine the stagnant waters in
localities where they occur, and deal with them so as to destroy the
larvae. These little creatures are remarkable from the heads and thorax
being larger and more distinct than in other Dipterous larvae. Their
metamorphoses have been frequently described, and recently the numerous
interesting points connected with their life-histories have been admirably
portrayed by Professor Miall,[377] in an accessible form, so that it is
unnecessary for us to deal with them. _Corethra_ is placed in Culicidae,
but the larva differs totally from that of _Culex_; it is predaceous in
habits, is very transparent, has only an imperfect tracheal system, without
spiracles, and has two pairs of air-sacs (perhaps we should rather say
pigmented structures possibly for aerostatic purposes, but not suppliers of
oxygen). The kungu cake mentioned by Livingstone as used on Lake Nyassa is
made from an Insect which occurs in profusion there, and is compressed into
biscuit form. It is believed to be a _Corethra_. One of the peculiarities
of this family is the prevalence of scales on various parts of the body,
and even on the wings: the scales are essentially similar to those of
Lepidoptera. Though Mosquitoes are generally obscure plain Insects, there
are some—in the South American genus _Megarrhina_—that are elegant,
beautifully adorned creatures. Swarms of various species of Culicidae,
consisting sometimes of almost incalculable numbers {468}of individuals,
occur in various parts of the world; one in New Zealand is recorded as
having been three-quarters of a mile long, twenty feet high, and eighteen
inches thick. There is good reason for supposing that Mosquitoes may act as
disseminators of disease, but there is no certain evidence on the subject.
The minute _Filaria_ that occurs in great numbers in some patients, is
found in the human body only in the embryonic and adult conditions. Manson
considers that the intermediate stages are passed in the bodies of certain
Mosquitoes.[378]
FAM. 5. CHIRONOMIDAE (_Gnats_, _Midges_).—_Small or minute flies of slender
form, with narrow wings, without projecting rostrum, usually with densely
feathered antennae in the male, and long slender legs._ The flies of this
family bear a great general resemblance to the Culicidae. They are much
more numerous in species, and it is not improbable that we have in this
country 200 species of the genus _Chironomus_ alone. They occur in enormous
numbers, and frequently form dancing swarms in the neighbourhood of the
waters they live in. The species are frequently extremely similar to one
another, though distinguished by good characters; they are numerous about
Cambridge. Many of them have the habit of using the front legs as feelers
rather than as means of support or locomotion. This is the opposite of what
occurs in Culicidae, where many of the species have a habit of holding up
the hind legs as if they were feelers. The eggs of _Chironomus_ are
deposited as strings surrounded by mucus, and are many of them so
transparent that the development of the embryo can be directly observed
with the aid of the microscope. They are said to possess a pair of
air-sacs. The larvae, when born, are aquatic in habits, and are destitute
of tracheal system. They subsequently differ greatly from the larvae of
_Culex_, inasmuch as the tracheal system that develops is quite closed, and
in some cases remains rudimentary. There is, however, much diversity in the
larvae and also in the pupae. The little Blood-worms, very common in many
stagnant and dirty waters, and used by anglers as bait, are larvae of
_Chironomus_. They are said to be αἱ Ἐμπίδες of Aristotle. The red colour
of these larvae is due to haemoglobin, a substance which has the power of
attracting and storing oxygen, and giving it off to the tissues as they
require it. Such larvae are able to live in burrows they construct
{469}amongst the mud. Some of them, provided plentifully with haemoglobin,
are in consequence able to live at great depths, it is said even at 1000
feet in Lake Superior, and come to the surface only occasionally. A few are
able even to tolerate salt water, and have been fished up from considerable
depths in the sea. It is a remarkable fact that these physiological
capacities differ greatly within the limits of the one genus, _Chironomus_,
for some of these species are destitute of haemoglobin, and have to live
near the surface of the water; these have a superior development of the
tracheal system. The pupae of _Chironomus_ have the legs coiled, and the
thorax, instead of being provided with the pair of tubes or trumpets for
breathing that is so common in this division of Diptera, have a pair of
large tufts of hair-like filaments.[379] A very curious form of
parthenogenesis has been described by Grimm[380] as existing in an
undetermined species of _Chironomus_, inasmuch as the pupa deposits eggs.
Although this form of parthenogenesis is of much interest, it is not in any
way to be compared with the case, already referred to, of _Miastor_ (p.
461). The "pupa" is at the time of oviposition practically the imago still
covered by the pupal integument; indeed Grimm informs us that in some
cases, after depositing a small number of ova, the pupa became an imago.
This parthenogenesis only occurs in the spring-generation; in the autumn
the development goes on in the natural manner. The case is scarcely
entitled to be considered as one of paedogenesis.
Gnats of this family, and believed to be a variety of _Chironomus
plumosus_, are subject to a curious condition, inasmuch as individuals
sometimes become luminous or "phosphorescent"; this has been noticed more
specially in Eastern Europe and Western Asia. The whole of the body and
legs may exhibit the luminous condition, but not the wings. It has been
suggested by Schmidt that this condition is a disease due to bacteria in
the body of the gnat.[381]
_Ceratopogon_ is a very extensive genus, and is to some extent anomalous as
a member of Chironomidae. The larvae exhibit considerable variety of form.
Some of them are aquatic {470}in habits, but the great majority are
terrestrial, frequenting trees, etc. The former larvae are very slender,
and move after the manner of leeches; they give rise to imagos with naked
wings, while the terrestrial larvae produce flies with hairy wings. There
are also important distinctions in the pupae of the two kinds; the
correlation between the habits, and the distinctions above referred to, is,
however, far from being absolutely constant.[382] Certain species of midges
are in this country amongst the most annoying of Insects; being of very
minute size, scarcely visible, they settle on the exposed parts of the body
in great numbers, and by sucking blood create an intolerable irritation.
_Ceratopogon varius_ is one of the most persistent of these annoyers in
Scotland, where this form of pest is much worse than it is in England; in
Cambridgeshire, according to Mr. G. H. Verrall, the two troublesome midges
are the females of _C. pulicaris_ and _C. bipunctatus_.
FAM. 6. ORPHNEPHILIDAE.—_Small, brown or yellowish flies, bare of
pubescence, with very large eyes contiguous in both sexes, and with
antennae composed of two joints and a terminal bristle; both the second
joint and the bristle are, however, really complex._ One of the smallest
and least known of the families of Diptera, and said to be one of the most
difficult to classify. The nervures of the wings are very distinct. Nothing
is known of the habits and metamorphoses; there is only one
genus—_Orphnephila_; it is widely distributed; we have one species in
Britain.
FAM. 7. PSYCHODIDAE (_Moth-flies_).—_Extremely small, helpless flies,
usually with thickish antennae, bearing much hair, with wings broader than
is usual in small flies, and also densely clothed with hair, giving rise to
a pattern more or less vague._ These flies are very fragile creatures, and
are probably numerous in species. In Britain forty or fifty species have
been recognised.[383] A South European form is a blood-sucker, and has
received the appropriate name of _Phlebotomus_. The life-history of
_Pericoma canescens_ has recently been studied by Professor Miall.[384] The
larva is of aquatic habits, but is amphibious, being capable of existing in
the air; it has a pair of anterior spiracles, by means {471}of which it
breathes in the air, and a pair at the posterior extremity of the body,
surrounded by four ciliated processes, with which it forms a sort of cup
for holding air when it is in the water. The favourite position is amongst
the filaments of green algae on which it feeds. A much more extraordinary
form of larva from South America, doubtless belonging to this family, has
recently been portrayed by Fritz Müller, under the name of _Maruina_.[385]
These larvae live in rapid waters in company with those of the genus
_Curupira_, and like the latter are provided with a series of suctorial
ventral discs. Fritz Müller's larvae belong to several species, and
probably to more than one genus, and the respiratory apparatus at the
extremity of the body exhibits considerable diversity among them.
FAM. 8. DIXIDAE.—The genus _Dixa_ must, it appears, form a distinct family
allying the Culicid series of families to the Tipulidae. The species are
small, gnat-like Insects, fond of damp places in forests. We have four
British species (_D. maculata_, _D. nebulosa_, _D. aestivalis_, _D.
aprilina_). The genus is very widely distributed, occurring even in
Australia. The larvae are aquatic, and have been described by Réaumur,
Miall, and Meinert. The pupa has the legs coiled as in the Culicidae.
FAM. 9. TIPULIDAE (_Daddy-long-legs, or Crane-flies_).—_Slender Insects
with elongate legs, a system of wing-nervures, rather complex, especially
at the tip; an angulate, or open V-shaped, suture on the dorsum of the
thorax in front of the wings: the female with the body terminated by a pair
of hard, pointed processes, concealing some other processes, and forming an
ovipositor._ The curious, silly Insects called daddy-long-legs are known
all over the world, the family being a very large one, and found
everywhere, some of its members extending their range even to the most
inclement climates. It includes a great variety of forms that would not be
recognised by the uninitiated, but can be readily distinguished by the
characters mentioned above. It is impossible to assign any reason of
utility for the extreme elongation of the legs of these Insects; as
everyone knows, they break off with great ease, and the Insect appears to
get on perfectly well without them. It is frequently {472}the case that
they are much longer in the males than in the females. Other parts of the
body exhibit a peculiar elongation; in some forms of the male the front of
the head may be prolonged into a rostrum. In a few species the head is
separated by a great distance from the thorax, the gap being filled by
elongate, hard, cervical sclerites; indeed it is in these Insects that the
phenomenon, so rare in Insect-structure, of the elongation of these
sclerites and their becoming a part of the actual external skeleton,
reaches its maximum. In several species of _Eriocera_ the male has the
antennae of extraordinary length, four or five times as long as the body,
and, strange to say, this elongation is accompanied by a reduction in the
number of the segments of which the organ is composed, the number being in
the male about six, in the female ten, in place of the usual fourteen or
sixteen. In _Toxorrhina_ and _Elephantomyia_ the proboscis is as long as
the whole body. In other forms the wings become elongated to an unusual
extent by means of a basal stalk. It is probable that the elongation of the
rostrum may be useful to the Insects. Gosse,[386] indeed, describes
_Limnobia intermedia_ as having a rostrum half as long as the body, and as
hovering like a Syrphid, but this is a habit so foreign to Tipulidae, that
we may be pardoned for suspecting a mistake. The larvae exhibit a great
variety of form, some being terrestrial and others aquatic, but the
terrestrial forms seem all to delight in damp situations, such as shaded
turf or rotten tree-stems. They are either amphipneustic or metapneustic,
that is, with a pair of spiracles placed at the posterior extremity of the
body; the aquatic species frequently bear appendages or projections near
these spiracles. The pupae in general structure are very like those of
Lepidoptera, and have the legs extended straight along the body; they
possess a pair of respiratory processes on the thorax in the form of horns
or tubes.
There are more than 1000 species of these flies known, and many genera.
They form three sub-families, which are by some considered distinct
families, viz.: Ptychopterinae, Limnobiinae or Tipulidae Brevipalpi,
Tipulinae or Tipulidae Longipalpi.
The Ptychopterinae are a small group in which the angulate {473}suture of
the mesonotum is indistinct; the larvae are aquatic and have the head free,
the terminal two segments of the body enormously prolonged (Fig. 223),
forming a long tail bearing, in the North American _Bittacomorpha_, two
respiratory filaments. Hart[387] describes this tail as possessing a
stigmatal opening at the extremity; no doubt the structure is a compounded
pair of spiracles. The pupa (Fig. 223, B) has quite lost the respiratory
tube at the posterior extremity of the body, but has instead quite as long
a one at the anterior extremity, due to one tube of the pair normal in
Tipulidae being enormously developed, while its fellow remains small. This
is a most curious departure from the bilateral symmetry that is so
constantly exhibited in Insect-structure. Our British species of
_Ptychoptera_ have the pupal respiratory tube as extraordinary as it is in
_Bittacomorpha_, though the larval tail is less peculiar.[388] This group
should perhaps be distinguished from the Tipulidae as a separate family,
but taxonomists are not yet unanimous as to this. Brauer considers that the
head of the larva, and the condition of five Malpighian tubules in the
imago, require the association of Ptychopterinae with the preceding
families (Chironomidae, etc.), rather than with the Tipulidae.
[Illustration: Fig. 223.—_Bittacomorpha clavipes._ North America x 2/1.
(After Hart.) A, Larva; B, pupa: _l_, the left, _r_, the right respiratory
tube.]
The great majority of the Tipulidae are comprised in the sub-family
Limnobiinae—the Tipulidae Brevipalpi of Osten Sacken:[389] in them the last
joint of the palpi is shorter or not much longer than the two preceding
together. They exhibit great variety, and many of them are types of
fragility. The common winter gnats of the genus _Trichocera_ are a fair
sample of this sub-family. The species of this genus mostly inhabit high
latitudes, and delight in {474}a low temperature; it has been said that
they may be seen on the wing in the depth of winter when the temperature is
below freezing, but it is pretty certain that the spots chosen by the
Insects are above that temperature, and Eaton states that the usual
temperature during their evolutions is about 40° or 45° Fahr. They often
appear in the damp conditions of a thaw when much snow is on the ground.
_T. simonyi_ was found at an elevation of 9000 feet in the Tyrol, crawling
at a temperature below the freezing-point, when the ground was deeply
covered with snow. _T. regelationis_ occurs commonly in mines even when
they are 500 feet or more deep. The most extraordinary of the Limnobiinae
is the genus _Chionea_, the species of which are totally destitute of wings
and require a low temperature. _C. araneoides_ inhabits parts of northern
Europe, but descends as far south as the mountains near Vienna; it is
usually said to be only really active in the depth of winter and on the
surface of the snow. More recently, however, a large number of specimens
were found by Professor Thomas in the month of October in his garden in
Thuringia; they were caught in little pit-falls constructed to entrap
snails. The larva of this Insect is one of the interesting forms that
display the transition from a condition with spiracles at the sides of the
body to one where there is only a pair at the posterior extremity.
A very peculiar Fly, in which the wings are reduced to mere slips,
_Halirytus amphibius_, was discovered by Eaton in Kerguelen Land, where it
is habitually covered by the rising tide. Though placed in Tipulidae, it is
probably a Chironomid.
The group Cylindrotomina is considered by Osten Sacken[390] to be to some
extent a primitive one having relationship with the Tipulinae; it was, he
says, represented by numerous species in North America during the Oligocene
period. It is of great interest on account of the larvae, which are in
several respects similar to caterpillars of Lepidoptera. The larva of
_Cylindrotoma distincta_ lives upon the leaves of plants—_Anemone_,
_Viola_, _Stellaria_—almost like a caterpillar; it is green with a crest
along the back consisting of a row of fleshy processes. Though this fly is
found in Britain the larva has apparently not been observed here. The
life-history of _Phalacrocera replicata_ has been recently published by
Miall and Shelford.[391] The larva eats {475}submerged mosses in the South
of England, and bears long forked filaments, reminding one of those of
caterpillars. This species has been simultaneously discussed by Bengtsson,
who apparently regards these Tipulids with caterpillar-like larvae—he calls
them Erucaeformia[392]—as the most primitive form of existing Diptera.
The Tipulinae—Tipulidae Longipalpi, Osten Sacken[393]—have the terminal
joint of the palpi remarkably long, longer than the three preceding joints
together. The group includes the largest forms, and the true
daddy-long-legs, a Chinese species of which, _Tipula brobdignagia_,
measures four inches across the expanded wings. The group contains some of
the finest Diptera. Some of the exotic forms allied to _Ctenophora_ have
the wings coloured in the same manner as they are in certain Hymenoptera,
and bear a considerable resemblance to members of that Order.
[Illustration: Fig. 224—Head of _Bibio_. × 10. A, Of male, seen from the
front; C, from the side; _a_, upper, _b_, lower eye; B, head of female.]
FAM. 10. BIBIONIDAE.—_Flies of moderate or small size, sometimes of
different colours in the two sexes, with short, thick, straight, antennae;
front tibiae usually with a long pointed process; coxae not elongate. Eyes
of male large, united, or contiguous in front._ The flies of the genus
_Bibio_ usually appear in England in the spring, and are frequently very
abundant; they are of sluggish habits and poor performers on the wing.
{476}[Illustration: Fig. 225—Larva of _Bibio_ sp. Cambridge. × 5.]
The difference in colour of the sexes is very remarkable, red or yellow
predominating in the female, intense black in the male; and it is a curious
fact that the same sexual distinction of colour reappears in various parts
of the world—England, America, India, and New Zealand; moreover, this
occurs in genera that are by no means closely allied, although allied
species frequently have concolorous sexes. The eyes of the males are well
worth study, there being a very large upper portion, and, abruptly
separated from this, a smaller, differently faceted lower portion,
practically a separate eye; though so largely developed the upper eye is in
some cases so hairy that it must greatly interfere with the formation of a
continuous picture. Carrière considers that the small lower eye of the male
corresponds to the whole eye of the female. The larvae of _Bibio_ (Fig.
225) are caterpillar-like in form, have a horny head, well developed,
biting mouth-organs, and spine-like processes on the body-segments. They
are certified by good authorities[394] to possess the extremely unusual
number of ten pairs of spiracles; a larva found at Cambridge, which we
refer to _Bibio_ (Fig. 225) has nine pairs of moderate spiracles, as well
as a large terminal pair separated from the others by a segment without
spiracles. The genus _Dilophus_ is closely allied to _Bibio_, the larvae of
which (and those of Bibionidae in general) are believed to feed on
vegetable substances; the parasitism of _Dilophus vulgaris_ on the larva of
a moth, _Epinotia_ (_Chaetoptria_) _hypericana_, as recorded by Meade,[395]
must therefore be an exceptional case. In the genus _Scatopse_ there is a
very important point to be cleared up as to the larval respiratory system;
it is said by Dufour and Perris[396] to be amphipneustic; there are,
however, nine projections on each side of the body that were considered by
Bouché, and probably with good reason, to {477}be spiracles. The food of
_Scatopse_ in the larval state is principally vegetable. The larva of
_Scatopse_ changes to a pupa inside the larval skin; the pupa is provided
on the thorax with two branched respiratory processes that project outside
the larval skin.[397] Lucas has given an interesting account of the
occurrence of the larva of _Bibio marci_ in enormous numbers at Paris; they
lived together in masses, there being apparently some sort of connection
between the individuals.[398] In the following year the fly was almost
equally abundant.
[Illustration: Fig. 226—Portion of integument of _Bibio_ sp. Cambridge.
_p_, Intersegmental processes; _s_, spiracle.]
Owing to the great numbers in which the species of Bibionidae sometimes
appear, these Insects have been supposed to be very injurious. Careful
inquiry has, however, generally exculpated them as doers of any serious
injury, though _Dilophus febrilis_—a so-called fever-fly—appears to be
really injurious in this country when it multiplies excessively, by eating
the roots of the hop-plant.
FAM. 11. SIMULIIDAE (_Sand-flies_, _Buffalo-gnats_).—_Small obese flies
with humped back, rather short legs and broad wings, with short, straight
antennae destitute of setae; proboscis not projecting._ There is only one
genus, _Simulium_, of this family, but it is very widely spread, and will
probably prove to be nearly cosmopolitan. Some of the species are notorious
from their blood-sucking habits, and in certain seasons multiply to an
enormous extent, alight in thousands on cattle, and induce a disease that
produces death in a few hours; it is thought as the result of an instilled
poison. _S. columbaczense_ has occasioned great losses amongst the herds
near the Danube; in North America the Buffalo- and Turkey-gnats attack a
variety of mammals and birds. In Britain {478}and other parts of the world
they do not increase in numbers to an extent sufficient to render them
seriously injurious: their bite is however very annoying and irritating to
ourselves. In their early stages they are aquatic and require well aërated
waters: the larvae hold themselves erect, fixed to a stone or some other
object by the posterior extremity, and have on the head some beautiful
fringes which are agitated in order to bring food within reach; the pupae
are still more remarkable, each one being placed in a pouch or sort of
watch-pocket, from which projects the upper part of the body provided with
a pair of filamentous respiratory processes. For an account of the
interesting circumstances connected with the metamorphoses of this species
the reader should refer to Professor Miall's book; and for the life-history
of the American Buffalo-gnat to Riley.[399]
FAM. 12. RHYPHIDAE.—This is another of the families that have only two or
three genera, and yet are very widely distributed. These little flies are
distinguished from other Nemocera Anomala (cf. p. 456) by _the presence of
a discal cell; the empodia of the feet are developed as if they were
pulvilli, while the true pulvilli remain rudimentary_. The larvae are like
little worms, being long and cylindric; they are amphipneustic, and have
been found in decaying wood, in cow-dung, in rotten fruits, and even in
dirty water. The "petite tipule," the metamorphoses of which were described
and figured by Réaumur, is believed to be the common _Rhyphus
fenestralis_.[400] _R. fenestralis_ is often found on windows, as its name
implies.
SERIES 2. ORTHORRHAPHA BRACHYCERA
FAM. 13. STRATIOMYIDAE.—_Antennae with three segments and a terminal
complex of obscure joints, frequently bearing an arista: tibiae not spined;
wings rather small, the anterior nervures usually much more strongly marked
than those behind. The median cell small, placed near to the middle of the
wing. Scutellum frequently spined; terminal appendages of the tarsi small,
but pulvilli and a pulvilliform empodium are {479}present._ This is a large
family, whose members are very diversified, consequently definition of the
whole is difficult. The species of the typical sub-family Stratiomyinae
generally have the margins of the body prettily marked with green or
yellow, and the scutellum spined. In the remarkable American genus,
_Hermetia_, the abdomen is much constricted at the base, and the scutellum
is not spined; in the division Sarginae the body is frequently of brilliant
metallic colours. The species all have an only imperfect proboscis, and are
not blood-suckers. The larvae are also of diverse habits; many of those of
the Stratiomyinae are aquatic, and are noted for their capacity of living
in salt, alkaline, or even very hot water. Mr. J. C. Hamon found some of
these larvae in a hot spring in Wyoming, where he could not keep his hand
immersed, and he estimated the temperature at only 20° or 30° Fahr. below
the boiling-point. The larva of _Stratiomys_ is of remarkably elongate,
strap-like, form, much narrowed behind, with very small head; the terminal
segment is very long and ends in a rosette of hairs which the creature
allows to float at the surface. After the larval skin is shed the pupa,
though free, is contained therein; the skin alters but little in form, and
has no organic connection with the pupa, which merely uses the skin as a
shield or float. These larvae have been very frequently described; they can
live out of the water. Brauer describes the larvae of the family as
"peripneustic, some perhaps amphipneustic." Miall says there are, in
_Stratiomys_, nine pairs of spiracles on the sides of the body which are
not open, though branches from the longitudinal air-tubes pass to them.
There are probably upwards of 1000 species of Stratiomyidae known, and in
Britain we have 40 or 50 kinds. The American genus _Chiromyza_, Wied., was
formerly treated by Osten Sacken as a separate family, Chiromyzidae, but
Williston places it in Stratiomyidae.
FAM. 14. LEPTIDAE, including XYLOPHAGIDAE and COENOMYIIDAE.—_The Leptidae
proper are flies of feeble build; antennae with three joints and a terminal
bristle; in the Xylophagidae the antennae are longer, and the third joint
is complex. The wings have five posterior cells, the middle tibiae are
spined. Pulvilli and a pulvilliform empodium present._ The three families
are considered distinct by most authors, but there has always been much
difficulty about the Xylophagidae and Coenomyiidae, we therefore treat them
as sub-families.
{480}[Illustration: Fig. 227—_Atherix ibis._ A, The fly, nat. size; B, mass
of dead flies overhanging water, much reduced.]
The Xylophaginae are a small group of slender Insects, perhaps most like
the short-bodied kinds of Asilidae; the third joint of the antenna is
vaguely segmented, and there is no terminal bristle. _Rhachicerus_ is a
most anomalous little fly with rather long stiff antennae of an almost
nemocerous character, the segments of which give off a short thick
prolongation on each side, reminding one of a two-edged saw. The three or
four British species of Xylophaginae are forest Insects, the larvae of
which live under bark, and are provided with a spear-like head with which
they pierce other Insects. The Coenomyiinae consist of the one genus
_Coenomyia_, with two or three European and North American species. They
are remarkably thick-bodied, heavy flies, reminding one somewhat of an
imperfect Stratiomyid destitute of ornamentation. The metamorphosis of _C.
ferruginea_ has been described by Beling.[401] The larva is not aquatic,
but lives in burrows or excavations in the earth where there are, or have
recently been, rotten logs; it is probably predaceous. It is cylindric,
with an extremely small head and eleven other segments, the stigma on the
first thoracic segment distinct; the terminal segment is rather broad, and
the structures surrounding the stigma are complex. The pupa has stigmata on
each of abdominal segments 2 to 8. Notwithstanding that the fly is so
different to _Xylophagus_, the larvae indicate the two forms as perhaps
really allied. One of the Leptinae, _Atherix ibis_, has a singular mode of
oviposition (Fig. 227), the females of the species deposit their eggs in
common, and, dying as they do so, add their bodies to the common mass,
which becomes an agglomeration, it may be of thousands of individuals, and
of considerable size. The mass is attached to a branch of a bush or to a
plant overhanging water, into which it {481}ultimately falls. These curious
accumulations are occasionally found in England as well as on the
Continent, but no reason for so peculiar a habit is at present forthcoming.
Still more remarkable are the habits of some European Leptids of the genera
_Vermileo_ (_Psammorycter_ of some authors) and _Lampromyia_, slender
rather small flies of Asilid-like appearance, the larvae of which form
pit-falls after the manner of the Ant-lion. According to Beling[402] the
larva of _Leptis_ is very active, and is distinguished by having the
stigmatic orifice surrounded by four quite equal, quadrangularly placed
prominences; and at the other extremity of the body a blackish, naked,
triangular plate; on the under side of each of seven of the abdominal
segments there is a band of spines. The larva of _Atherix_ has seven pairs
of abdominal feet. Altogether there are some two or three hundred known
species of Leptidae; our British species scarcely reach a score. They are
destitute of biting-powers and are harmless timid creatures. _Leptis
scolopacea_, the most conspicuous of our native species, a soft-bodied fly
of rather large size, the wings much marked with dark colour, and the
thick, pointed body yellowish, marked with a row of large black spots down
the middle, is a common Insect in meadows.
[Illustration: Fig. 228.—Larva of _Vermileo degeeri_ (_Psammorycter
vermileo_). A, lateral, B, dorsal view: _p_, an abdominal pseudopod; _st_,
stigma. Europe. (After Réaumur and Brauer.)]
FAM. 15. TABANIDAE (_Breeze-flies_, _Cleggs_, or _Horse-flies_, also
frequently called _Gad-flies_).—_Proboscis fleshy, distinct, enwrapping
pointed horny processes, palpi distinct, terminal joint inflated, pendent
in front of proboscis. Antennae projecting, four-jointed, second joint very
short, third variable in form, fourth forming an indistinctly segmented
continuation of the third, but not ending in a bristle. A perfect squama in
front of the halter. Eyes large, very large in the males, but laterally
extending, rather than globose._
{482}[Illustration: Fig. 229—_Pangonia longirostris._ x 1. Nepal. (After
Hardwicke.)]
This large and important family of flies, of which Williston states that
1400 or 1500 species are named, is well known to travellers on account of
the blood-sucking habits of its members; they have great powers of flight,
and alight on man and animals, and draw blood by making an incision with
the proboscis; only the females do this, the males wanting a pair of the
lancets that enable the other sex to inflict their formidable wounds. They
are comparatively large Insects, some of our English species of _Tabanus_
attaining an inch in length. The smaller, grey _Haematopota_, is known to
every one who has walked in woods or meadows in the summer, as it alights
quietly on the hands or neck and bites one without his having previously
been made aware of its presence. The larger Tabani hum so much that one
always knows when an individual is near. The species of _Chrysops_, in
habits similar to _Haematopota_, are remarkable for their beautifully
coloured golden-green eyes. In Brazil the Motuca fly, _Hadrus lepidotus_,
Perty, makes so large and deep a cut that considerable bleeding may follow,
and as it sometimes settles in numbers on the body, it is deservedly
feared. The most remarkable forms of Tabanidae are the species of the
widely distributed genus _Pangonia_ (Fig. 229). The proboscis in the
females of some of the species is three or four times the length of the
body, and as it is stiff and needle-like the creature can use it while
hovering on the wing, and will pierce the human body even through clothing
of considerable thickness. The males suck the juices of flowers. The Seroot
fly, that renders some of the districts of Nubia uninhabitable for about
three months of the year, appears, from the figure and description given by
Sir Samuel Baker, to be a _Pangonia_. Tabanidae are a favourite food of the
fossorial wasps of the family Bembecidae. These wasps are apparently aware
of the blood-sucking habits of their favourites, and attend on travellers
and pick up the flies as they are about to settle down to their phlebotomic
operations. The larvae of the Tabanidae are some {483}of them aquatic, but
others live in the earth or in decaying wood; they are of predaceous
habits, attacking and sucking Insect-larvae, or worms. Their form is
cylindric, attenuate at the two extremities; the slender small head is
retractile, and armed with a pair of conspicuous, curved black hooks. The
body is surrounded by several prominent rings. The breathing apparatus is
apparently but little developed, and consists of a small tube at the
extremity of the body, capable of being exserted or withdrawn; in this two
closely approximated stigmata are placed. In a larva, probably of this
family, found by the writer in the shingle of a shallow stream in the New
Forest, the annuli are replaced by seven circles of prominent pseudopods,
on the abdominal segments about eight in each circle, and each of these
feet is surmounted by a crown of small hooks, so that there are fifty or
sixty feet distributed equally over the middle part of the body without
reference to upper or lower surface. The figures of the larva of _T.
cordiger_, by Brauer, and of _Haematopota pluvialis_, by Perris, are
something like this, but have no setae on the pseudopods. The metamorphoses
of several Tabanidae are described and figured by Hart;[403] the pupa is
remarkably like a Lepidopterous pupa. We have five genera and about a score
of species of Tabanidae in Britain.
[Illustration: Fig. 230—Larva of a Tabanid. [? _Atylotus fulvus._] A, the
larva, × 3; B, head; C, end of body; D, one of the pseudopods. New Forest.]
FAM. 16. ACANTHOMERIDAE.—A very small family of two genera (_Acanthomera_
and _Rhaphiorhynchus_) confined to America, and including the largest
Diptera, some being two inches long. The antenna is terminated by a
compound of seven segments and a style; the proboscis is short, and the
squama rudimentary. The general form reminds one of Tabanidae or Oestridae.
A dried larva exists in the Vienna collection; it is amphipneustic, and
very remarkable on account of the great size of the anterior stigma.
{484}FAM. 17. THEREVIDAE.—_Moderate-sized flies, with somewhat the
appearance of short Asilidae. They have, however, only a feeble fleshy
proboscis, and minute claws, with pulvilli but no empodium; the antennae
project, are short, three-jointed, pointed._—The flies of this family are
believed to be predaceous like the Robber-flies, but they appear to be very
feebly organised for such a life. We have about ten species in Britain, and
there are only some 200 known from all the world. But little is known as to
the metamorphoses. Meigen found larvae of _T. nobilitata_ in rotten stumps,
but other larvae have been recorded as devouring dead pupae or larvae of
Lepidoptera. The larvae are said to be elongate, very slender, worm-like,
and to have nineteen body-segments, the posterior pair of spiracles being
placed on what looks like the seventeenth segment, but is really the eighth
of the abdomen. The pupa is not enclosed in the larval skin; that of
_Psilocephala_ is armed with setae and spinous processes, and was found in
rotten wood by Frauenfeld.
[Illustration: Fig. 231—_Thereva (Psilocephala) confinis._ A, Pupa; B,
larva. Europe. (After Perris.)]
FAM. 18. SCENOPINIDAE.—_Rather small flies, without bristles. Antennae
three-jointed, the third joint rather long, without appendage. Proboscis
not projecting. Empodium absent._ These unattractive flies form one of the
smallest families, and are chiefly found on windows. _S. fenestralis_ looks
like a tiny Stratiomyid, with a peculiar, dull, metallic surface. The larva
of this species has been recorded as feeding on a variety of strange
substances, but Osten Sacken is of opinion[404] that it is really
predaceous, and frequents these substances in order to find the larvae that
are developing in them. If so, _Scenopinus_ is useful in a small way by
destroying "moth," etc. The larva is a little slender, cylindrical, hard,
pale worm of nineteen segments, with a small brown head placed like a hook
at one extremity of the body and with two short, divergent processes at the
other extremity, almost exactly like the larva of _Thereva_. Full
references to the literature about this Insect are given by Osten Sacken.
FAM. 19. NEMESTRINIDAE.—These Insects appear to be allied to the
Bombyliidae. _They are of medium size, often pilose, and {485}sometimes
with excessively long proboscis; antennae short, with a simple third joint,
and a jointed, slender, terminal appendage; the tibiae have no spurs, the
empodium is pulvillus-like. The wing-nervuration is perhaps the most
complex found in Diptera, there being numerous cells at the tip, almost
after the fashion of Neuroptera._ With this family we commence the aerial
forms composing the Tromoptera of Osten Sacken. Nemestrinidae is a small
family of about 100 species, but widely distributed. _Megistorhynchus
longirostris_ is about two-thirds of an inch long, but has a proboscis at
least four times as long as itself. In South Africa it may be seen
endeavouring to extract, with this proboscis, the honey from the flower of
a _Gladiolus_ that has a perianth just as long as its own rostrum; as it
attempts to do this when it is hovering on the wing, and as the proboscis
is, unlike that of the Bombylii, fixed, the Insect can only succeed by
controlling its movements with perfect accuracy; hence it has great
difficulty in attaining its purpose, especially when there is much wind,
when it frequently strikes the earth instead of the flower. M. Westermann
thinks[405] the life of the Insect and the appearance and duration of the
flower of the _Gladiolus_ are very closely connected. The life-history of
_Hirmoneura obscura_ has recently been studied in Austria by Handlirsch and
Brauer.[406] The larva is parasitic on the larva of a Lamellicorn beetle
(_Rhizotrogus solstitialis_); it is metapneustic, and the head is highly
modified for predaceous purposes. The young larva apparently differs to a
considerable extent from the matured form. The most curious fact is that
the parent fly does not oviposit near the Lamellicorn-larva, but places her
eggs in the burrows of some wood-boring Insect in logs; the larvae when
hatched come to the surface of the log, hold themselves up on their hinder
extremity and are carried away by the wind; in what manner they come into
contact with the Lamellicorn larva, which feeds in turf, is unknown. The
pupa is remarkable on account of the prominent, almost stalked stigmata,
and of two pointed divergent processes at the extremity of the body. This
life-history is of much interest, as it foreshadows to some extent the
complex parasitic life-histories of Bombyliidae. The Nemestrinidae are not
represented in the British fauna.
{486}[Illustration: Fig. 232—_Argyromoeba trifasciata._ A, Young larva; B,
adult larva; C, pupa. France. (After Fabre.) A, Greatly, B, C, slightly
magnified.]
FAM. 20. BOMBYLIIDAE.—_Body frequently fringed with down, or covered in
large part with hair. Legs slender, claws small, without distinct empodium,
usually with only minute pulvilli. Proboscis very long or moderate,
antennae three-jointed, terminal joint not distinctly divided, sometimes
large, sometimes hair-like._ This is a very large family, including 1500
species, and is of great importance to both naturalist and economist. Two
well-marked types, formerly treated as distinct families, are included in
it—(1) the Bombyliides with very long exserted rostrum, and humped thorax;
and (2) Anthracides, with a short beak, and of more slender and graceful
form. None of these flies are bloodsuckers, they frequent flowers only, and
use their long rostrums in a harmless manner. The members of both of these
groups usually have the wings ornamented with a pattern, which in _Anthrax_
is frequently very remarkable; in both, the clothing of the body is
frequently variegated. Their powers of flight are very great, and the
hovering _Bombylius_ of early spring is endowed with an unsurpassed
capacity for movement, remaining perfectly still on the wing, and darting
off with lightning rapidity; _Anthrax_ is also most rapid on the wing. In
Britain we have but few species of Bombyliidae, but in warm and dry
climates they are very numerous. The life-history of these Insects was till
recently unknown, but that of _Argyromoeba_ (_Anthrax_) _trifasciata_ has
been described by the French naturalist, Fabre, who ascertained that the
species is parasitic on the Mason-bee, _Chalicodoma muraria_, that forms
nests of solid masonry. He endeavoured to discover the egg, but failed; the
parent-fly oviposits, it appears, by merely dropping a minute egg while
flying over the surface of the mass of masonry by which the grubs of the
_Chalicodoma_ are protected. From this egg there is hatched a minute
delicate vermiform larva (Fig. 232, A). In order to obtain its food, it is
necessary for this feeble creature to penetrate the masonry; apparently a
hopeless task, the animal {487}being scarcely a twentieth of an inch long
and very slender; it is, however, provided with a deflexed horny head,
armed in front with some stiff bristles, while on the under surface of the
body there are four pairs of elongate setae serving as organs of
locomotion; thus endowed, the frail creature hunts about the surface of the
masonry, seeking to find an entrance; frequently it is a long time before
it is successful; but though it has never taken any food it is possessed of
great powers of endurance. Usually, after being disclosed from the egg, it
remains about fifteen days without stirring; and even after it commences
its attempts to enter the nest it is still capable of a long life without
taking any food. Possibly its organisation will not permit it to feed
(supposing any food were obtainable by it) without its growing somewhat
thereafter, and if so, its chance of obtaining entrance through the masonry
would be diminished. Abstention, it would appear, is the best policy,
whether inevitable or not; so the starving little larva continues its
endeavours to find a chink of entrance to the food contained in the
interior of the masonry. It has plenty of time for this, because it is
better for it not to get into the cell of the bee until the grub is quite
full grown, and is about to assume the pupal form, when it is quite
incapable of self-defence. Finally, after greater or less delay, the
persevering little larva succeeds in finding some tiny gap in the masonry
through which it can force itself. M. Fabre says that the root of a plant
is not more persistent in descending into the soil that is to support it
than is this little _Anthrax_ in insinuating itself through some crack that
may admit it to its food. Having once effected an entrance the organisation
that has enabled it to do so is useless; this primary form of the larva
has, in fact, as its sole object to enable the creature to penetrate to its
food. Having penetrated, it undergoes a complete change of form, and
appears as a creature specially fitted for feeding on the quiescent larva
of the bee without destroying it. To accomplish this requires an extreme
delicacy of organisation and instinct; to bite the prey would be to kill
it, and if this were done, the _Anthrax_ would, Fabre supposes, ensure its
own death, for it cannot feed on the dead and putrefying grub; accordingly,
the part of its body that does duty as a mouth is merely a delicate sucker
which it applies to the skin of the _Chalicodoma_-grub; and thus without
inflicting any perceptible wound it sucks day {488}after day, changing its
position frequently, until it has completely emptied the pupa of its
contents, nothing being left but the skin. Although this is accomplished
without any wound being inflicted, so effectual is the process that all the
_Chalicodoma_ is gradually absorbed. The time requisite for completely
emptying the victim is from twelve to fifteen days; at the end of this time
the _Anthrax_-larva is full grown, and the question arises, how is it to
escape from the cell of solid masonry in which it is imprisoned? It entered
this cell as a tiny, slender worm through a minute orifice or crack, but it
has now much increased in size, and exit for a creature of its organisation
is not possible. For some months it remains a quiescent larva in the cell
of the _Chalicodoma_, but in the spring of the succeeding year it undergoes
another metamorphosis, and appears as a pupa provided with a formidable
apparatus for breaking down the masonry by which it is imprisoned. The head
is large and covered in front with six hard spines, to be used in striking
and piercing the masonry, while the other extremity of the body bears some
curious horns, the middle segments being armed with rigid hairs directed
backwards, and thus facilitating movement in a forward direction and
preventing slipping backwards. The pupa is strongly curved, and fixes
itself by the aid of the posterior spines; then, unbending itself, it
strikes with the armour of the other extremity against the opposing wall,
which is thus destroyed piecemeal until a gallery of exit is formed; when
this is completed the pupa-skin bursts and the perfect fly emerges, leaving
the pupa-case still fixed in the gallery. Thus this species appears in four
consecutive forms—in addition to the egg—each of which is highly
specialised for the purposes of existence in that stage.
The habits of our British _Bombylius major_ have been partially observed by
Dr. Chapman,[407] and exhibit a close analogy with those of _Anthrax
trifasciata_. The bee-larva that served as food was in this case _Andrena
labialis_, and the egg was deposited by the fly, when hovering, by jerking
it against the bank in which the nest of the bee was placed.
It has recently been discovered that the larvae of various species of
Bombyliidae are of great service by devouring the eggs of locusts. Riley
found that the egg-cases of _Caloptenus {489}spretus_ are emptied of their
contents by the larvae of _Systoechus oreas_ and _Triodites mus_. A similar
observation has been made in the Troad by Mr. Calvert, who found that the
Bombyliid, _Callostoma fascipennis_, destroys large quantities of the eggs
of _Caloptenus italicus_. Still more recently M. Künckel d'Herculais has
discovered that the destructive locust _Stauronotus maroccanus_ is kept in
check in Algeria in a similar manner, as many as 80 per cent of the eggs of
the locust being thus destroyed in certain localities. He observes that the
larva of the fly, after being full fed in the autumn, passes the winter in
a state of lethargy—he calls it "hypnody"—in the egg-case of the locust,
and he further informs us that in the case of _Anthrax fenestralis_, which
devours the eggs of the large _Ocnerodes_, the lethargy may be prolonged
for a period of three years. After the pupa is formed it works a way out of
the case by means of its armature, and then again becomes for some days
immobile before the perfect fly appears. Lepidopterous larvae are also
attacked by Bombyliid flies. A species of _Systropus_ has been recorded as
destroying the larva of _Limacodes_. Several of the Bombyliids of the genus
just mentioned are remarkable for the great resemblance they display to
various Hymenoptera, some of them being very slender flies, like the thin
bodied fossorial Hymenoptera. The difference between the pupa and imago in
this case is very remarkable (Fig. 233).
[Illustration: Fig. 233—_Systropus crudelis._ South Africa. A, Pupa; B,
imago, appendages of the left side removed. (After Westwood.)]
FAM. 21. ACROCERIDAE or CYRTIDAE.—_Flies of the average size, of peculiar
form, the small head consisting almost entirely of the eyes, and bent down
under the humped thorax: wings small, halteres entirely concealed by the
very large horizontal squamae; antennae very diverse._ The peculiar shape
of these flies is an exaggeration of that we have already noticed in
_Bombylius_. The mouth in Acroceridae is very variable; there may be a very
long, slender proboscis (_Acrocera_), or the mouth-parts may be so
atrophied that it is doubtful whether even an orifice exists (_Ogcodes_).
There are but {490}few species known, and all of them are rare;[408] in
Britain we have but two (_Ogcodes gibbosus_, _Acrocera globulus_). The
genus _Pterodontia_, found in North America and Australia, an inflated
bladder-like form with a minute head, is amongst the most extraordinary of
all the forms of Diptera. The habits are very peculiar, the larvae, so far
as known, all living as parasites within the bodies of spiders or in their
egg-bags. It appears, however, that the flies do not oviposit in
appropriate places, but place their eggs on stems of plants, and the young
larvae have to find their way to the spiders. Brauer has described the
larva of the European _Astomella lindeni_,[409] which lives in the body of
a spider, _Cteniza ariana_; it is amphipneustic and maggot-like, the head
being extremely small. The larva leaves the body of the spider for
pupation; the pupa is much arched, and the head is destitute of the
peculiar armature of the Bombyliidae, but has a serrate ridge on the
thorax. Emerton found the larvae of an _Acrocera_ in the webs of a common
North American spider, _Amaurobius sylvestris_, they having eaten, it was
supposed, the makers of the cobwebs.
[Illustration: Fig. 234—_Megalybus gracilis._ × 4. (Acroceridae.) Chili.
(After Westwood.)]
FAM. 22. LONCHOPTERIDAE.—_Small, slender flies, with pointed wings, short,
porrect antennae, with a simple, circular third joint, bearing a bristle;
empodium very small, pulvilli absent._—Only one genus of these little flies
is known, but it is apparently widely distributed, and its members are
common Insects. They have the appearance of Acalyptrate Muscidae, and the
nervuration of the wing is somewhat similar, the nervures being simple and
parallel, and the minute cross-nervures placed near the base. The
systematic position is somewhat doubtful, and the metamorphoses are but
incompletely known, very little having been added to what was discovered by
Sir John Lubbock in 1862.[410] The larva lives on the earth under vegetable
matter; it is very transparent, amphipneustic, with a peculiar head, and
with fringes on the margins. This larva changes to a semi-pupa or apterous
maggot-like form, within the larval skin; the true pupa was {491}not
noticed by Lubbock, but Frauenfeld[411] has since observed it, though he
only mentions that it possesses differentiated limbs and segments. The
metamorphoses appear to be very peculiar. This fly requires a thorough
study.
FAM. 23. MYDAIDAE.—_Large flies of elongate form; the hind femora long and
toothed beneath; the antennae knobbed at the tip, projecting, rather long,
the basal joint definite, but the divisions of the subsequent joints more
or less indistinct. Empodium small. Wings frequently heavily pigmented;
with a complex nervuration._ These fine flies are exotic; a few species
occur in the Mediterranean region, even in the South of Europe; the chief
genus, _Mydas_, is South American, but most of the other genera are
Australian or African. But little is known as to the life-histories. The
larvae are thought to live in wood, and to prey on Coleopterous larvae.
FAM. 24. ASILIDAE (_Robber-flies_).—_Mouth forming a short, projecting
horny beak, the palpi usually only small; the feet generally largely
developed; the claws large, frequently thick and blunt, the pulvilli
generally elongate, the empodium a bristle; halteres free; no squama._ The
Asilidae is one of the largest families of flies, and probably includes
about 3000 described species: as will readily be believed, there is much
variety of form; some are short and thick and extremely hairy,
superficially resembling hairy bees, but the majority are more or less
elongate, the abdomen being specially long, and having eight segments
conspicuously displayed. The antennae are variable, but are three-jointed
with a terminal appendage of diverse form and structure. They belong to the
super-family Energopoda of Osten Sacken, but the association of Empidae and
Dolichopidae with them does not seem to be very natural. In their perfect
state these flies are most voracious, their prey being Insects, which they
seize alive and impale with the rostrum. They are amongst the most
formidable of foes and fear nothing, wasps or other stinging Insects being
attacked and mastered by the stronger species without difficulty. They have
been observed to capture even dragon-flies and tiger-beetles. As is the
case with so many other Insects that prey on living Insects, the appetite
in the Asilidae seems to be insatiable; a single individual has been
observed to kill eight moths in twenty minutes. They have {492}been said to
suck blood from Vertebrates, but this appears to be erroneous. The
metamorphoses of a few species have been observed. Perris has called
attention to the close alliance between the larvae of Tabanidae and of
Asilidae,[412] and it seems at present impossible to draw a line of
distinction between the two. So far as is known, the larvae of Asilidae are
terrestrial and predaceous, attacking more particularly the larvae of
Coleoptera, into which they sometimes bore; in _Laphria_ there are numerous
pseudopods, somewhat of the kind shown in Fig. 230, but less perfect and
without hairs; the head and breathing organs appear to be very different.
According to Beling's descriptions of the larvae of _Asilus_, the head in
this case is more like that of the figure, but there are no pseudopods. The
flies of Asilidae and Tabanidae are so very distinct that these
resemblances between their larvae are worthy of note.
FAM. 25. APIOCERIDAE.—_Moderate-sized flies marked with black and white,
with an appearance like that of some Muscidae and Asilidae; with clear
wings, the veins not deeply coloured; antennae short, with a short, simple
appendage; no empodium._ But little is known as to the flies of this
family, of which only two genera, consisting of about a dozen species, are
found in North America, Chili, and Australia. Osten Sacken is inclined to
treat them as an aberrant division of Asilidae. Brauer looks on them as
primitive or synthetic forms of much interest, and has briefly described a
larva which he considers may be that of _Apiocera_, but this is doubtful;
it is a twenty-segmented form, and may be that of a _Thereva_.[413]
FAM. 26. EMPIDAE.—_Small or moderate-sized flies of obscure colours, grey,
rusty, or black, with small head, somewhat globular in form, with
three-jointed antennae, the terminal joint long and pointed; usually there
is a long slender beak; the legs are elongate, frequently hairy; the tarsi
bear long pulvilli and a small empodium._ The Empidae are an extensive
family of flies, with predaceous habits, the rostrum being used by the
female as an instrument for impaling and sucking other flies. They are
occasionally very numerous in individuals, especially in wooded districts.
There is great variety; there are nearly 200 species in Britain. The forms
placed in the sub-family Hybotinae are curious slender little Insects, with
very convex thorax and {493}large hind legs. In _Hemerodromia_ the front
legs are raptorial, the femora being armed with spines on which the tibiae
close so as to form a sort of trap. Many Empidae execute aërial dances, and
some of the species of the genus _Hilara_ are notorious for carrying veils
or nets in the form of silken webs more or less densely woven. This subject
is comparatively new, the fact having been discovered by Baron Osten Sacken
in 1877,[414] and it is not at all clear what purpose these peculiar
constructions serve; it appears probable that they are carried by means of
the hind legs, and only by the males. Mik thinks that in _H. sartor_ the
veil acts as a sort of parachute, and is of use in carrying on the aërial
performance, or enhancing its effect; while in the case of other species,
_H. maura_ and _H. interstincta_, the object appears to be the capture or
retention of prey, after the manner of spiders. The source of the silk is
not known, and in fact all the details are insufficiently ascertained. The
larvae of Empidae are described as cylindrical maggots, with very small
head, and imperfect ventral feet; the stigmata are amphipneustic, the
thoracic pair being, however, excessively small; beneath the posterior pair
there is nearly always a tooth- or spine-like prominence present.
[Illustration: Fig. 235—A, Larva, B, pupa of _Medeterus ambiguus_. France.
(After Perris.)]
FAM. 27. DOLICHOPIDAE.—_Graceful flies of metallic colours, of moderate or
small size, and long legs; usually with bristles on the thorax and legs,
the halteres exposed, squamae being quite absent; antennae of two short
stout joints (of which the second is really two, its division being more or
less distinct), with a thread-like or hair-like appendage. Proboscis short,
fleshy. Claws, pulvilli, and empodium small; wings with a simple system of
nervures, those on the posterior part of the wing are but few, there is no
anterior basal cross-vein between the discal and second basal cells, which
therefore form but one cell._ This is also a very extensive family of
flies, of which we have probably about 200 species in Britain. They are
conspicuous on account of their golden, or golden-green colours, only a few
being yellow or black. {494}The males are remarkable for the curious
special characters they possess on the feet, antennae, face, or wings.
These characters are not alike in any two species; they are believed to be
of the nature of ornaments, and according to Professor Aldrich and others
are used as such in courtship.[415] This family of flies approaches very
closely to some of the Acalyptrate Muscidae in its characters. It is united
by Brauer with Empidae to form the tribe Orthogenya. Although the species
are so numerous and abundant in Europe, little is known as to their
metamorphoses. Some of the larvae frequent trees, living under the bark or
in the overflowing sap, and are believed to be carnivorous; they are
amphipneustic; a cocoon is formed, and the pupa is remarkable on account of
the existence of two long horns, bearing the spiracles, on the back of the
thorax; the seven pairs of abdominal spiracles being excessively
minute.[416]
[Illustration: Fig. 236—Wing of _Trineura aterrima_, one of the Phoridae.
Britain.]
SERIES 3. CYCLORRHAPHA ASCHIZA
FAM. 28. PHORIDAE.—_Small flies, with very convex thorax, small head, very
small two-jointed antennae, bearing a long seta; femora more or less broad;
wings with two dark, thick, approximate veins, meeting on the front margin
near its middle, and besides these, three or four very fine veins, that run
to the margins in a sub-parallel manner without forming any cells or
forks._ This obscure family of flies is of small extent, but its members
are extremely common in Europe and North America, where they often occur in
numbers running on the windows of houses. It is one of the most isolated
groups of Diptera, and great difference of opinion prevails as to its
classification. The wing-nervuration is peculiar (but varies somewhat in
the species), the total absence of any cross-veins even on the basal part
of the wing being remarkable. There are bristles on the head and thorax,
but they are not arranged in a regular manner. The larvae live in a great
variety of animal and vegetable decaying matter, {495}and attack living
Insects, and even snails, though probably only when these are in a sickly
or diseased condition. The metamorphoses of several species have been
described.[417] The larvae are rather slender, but sub-conical in form,
with eleven segments and a very small head, amphipneustic, the body behind
terminated by some pointed processes. The pupa is remarkable; it is
contained in a case formed by the contracted and hardened skin of the
larva; though it differs much in form from the larva the segmentation is
distinct, and from the fourth segment there project two slender processes.
These are breathing organs, attached to the prothorax of the imprisoned
pupa; in what manner they effect a passage through the hardened larval skin
is by no means clear. Perris supposes that holes for them pre-exist in the
larval skin, and that the newly-formed pupa by restless movements succeeds
in bringing the processes into such a position that they can pass through
the holes. The dehiscence of the puparium seems to occur in a somewhat
irregular manner, as in _Microdon_; it is never Cyclorrhaphous, and
according to Perris is occasionally Orthorrhaphous; probably there is no
ptilinum.
[Illustration: Fig. 237—_Aenigmatias blattoides._ × 27. Denmark. (After
Meinert.)]
The Insect recently described by Meinert as _Aenigmatias blattoides_,[418]
is so anomalous, and so little is known about it, that it cannot at present
be classified. It is completely apterous; the arrangement of the
body-segments is unlike that of Diptera, but the antennae and mouth-parts
are said to be like those of Phoridae. The Insect was found near Copenhagen
under a stone in the runs of _Formica fusca_. Meinert thinks it possible
that the discovery of the male may prove _Aenigmatias_ to be really allied
to Phoridae, and Mik suggests that it may be the same as _Platyphora
lubbocki_, Verrall, known to be parasitic on ants. Dahl recently described
a wingless Dipteron, found living as a parasite on land-snails in the
Bismarck archipelago, under the name of _Puliciphora lucifera_, {496}and
Wandolleck has recently made for this and some allies the new family
Stethopathidae. It seems doubtful whether these forms are more than
wingless Phoridae.
FAM. 29. PLATYPEZIDAE.—_Small flies, with porrect three-jointed antennae,
first two joints short, third longer, with a terminal seta; no bristles on
the back; hind legs of male, or of both sexes, with peculiar, broad, flat
tarsi; the middle tibiae bear spurs; there is no empodium._ Platypezidae is
a small family of flies, the classification of which has always been a
matter of considerable difficulty, and is still uncertain. The larvae are
broad and flat, fringed at the margin with twenty-six spines; they live
between the lamellae of Agaric fungi. At pupation the form alters but
little; the imago emerges by a horizontal cleft occurring at the margins of
segments two and four.[419] We have four genera (_Opetia_, _Platycnema_,
_Platypeza_, _Callomyia_), and nearly a score of species of Platypezidae in
our British list, but very little seems to be known about them. There is
much difference in the eyes of the sexes, in some at any rate of the
species, they being large and contiguous in the male, but widely separated
in the female.
[Illustration: Fig. 238—Head of _Pipunculus_ sp. A, Seen from in front; B,
side view, showing an antenna magnified. Pyrenees.]
FAM. 30. PIPUNCULIDAE.[420]—_Small flies, with very short antennae bearing
a long seta that is not terminal; head almost globular, formed, except at
the back, almost entirely by the large conjoined eyes; the head is only
slightly smaller in the female, but in the male the eyes are more
approximate at the top._ This is another of the small families of flies,
that seems distinct from any other, though possessing no very important
characters. In many of the flies that have very large eyes, the head is
either flattened (_i.e._ compressed from before backwards, as in Tabanidae,
Asilidae), or forced beneath the humped thorax (as in Acroceridae), but
neither of these conditions exists in _Pipunculus_; in them the head
extends far forwards, so that the area of the {497}eye compared with the
size of the body is perhaps greater than in any other Diptera. The general
form is somewhat that of _Anthrax_, but the venation on the hind part of
the wing is much less complex. There is a remarkable difference between the
facets on the front and the back of these great eyes. We have three genera
and about a dozen species of Pipunculidae in Britain but apparently they
are far from common Insects. What is known about the life-history is almost
confined to an imperfect observation by Boheman, who found the larva of _P.
fuscipes_ living after the manner of a Hymenopterous parasite in the body
of a small Homopterous Insect.[421] The pupa seems to be of the type of
that of Syrphidae.
FAM. 31. CONOPIDAE.—_Elegant flies of moderate size, of varied colours,
with abdomen slender at the base, at the tip strongly incurved and thicker;
antennae inserted close together on a prominence, three-jointed, first
joint sometimes very short. The upper surface of the body without bristles
or with but few. There is a slender, elongate proboscis, which is
retractile and usually invisible._ This rather small family of flies
includes some of the most remarkable forms of Diptera; it includes two
divisions, the Conopinae with long antennae terminated by a very minute
pointed process, and Myopinae with shorter antennae bearing a hair that is
not placed at the end of the third joint. The former are the more wasp-like
and elegant; the Myopinae being much more like ordinary flies, though they
frequently have curious, inflated heads, with a white face. The mode of
life of the larva of _Conops_ is peculiar, it being parasitic in the
interior of _Bombus_, or other Hymenoptera. They have been found to attack
_Bombus_, _Chalicodoma_, _Osmia_, _Vespa_, _Pompilus_, and other Aculeates.
Williston says that Orthoptera are also attacked. _Conops_ has been seen to
follow Bumble-bees and alight on them, and Williston says this act is
accompanied by oviposition, the larva that is hatched boring its way into
the body of the bee. Others have supposed that the flies enter the bees'
nests and place their eggs in the larvae or pupae; but this is uncertain,
for _Conops_ has never been reared from a bee-larva or pupa, though it has
frequently been procured from the imago: cases indeed having been recorded
in which _Conops_ has emerged from the body {498}of a _Bombus_ several
months after the latter had been killed and placed in an entomologist's
collection. The larva is broad, and when full grown apparently occupies
nearly all the space of the interior of the abdomen of the bee; it has very
peculiar terminal stigmata. The pupa is formed in the larval skin, which is
greatly shortened and indurated for the purpose; this instar bears, in
addition to the posterior stigmata, a pair of slightly projecting, anterior
stigmata. We have several species of Conopidae in Britain; those belonging
to the division Conopinae are all rare Insects, but the Myopinae are not so
scarce; these latter are believed to be of similar habits with the
Conopinae, though remarkably little is known about them. This is another of
the numerous families, the relations of which are still a subject for
elucidation. Brauer places the Conopidae in his section Schizophora away
from Syrphidae, but we do not comprehend on what grounds; an inspection of
the head shows that there is no frontal lunule as there is in Eumyiidae;
both _Myopa_ and _Conops_ agreeing fairly well with _Syrphus_ as to this.
We therefore place the family in its old position near _Syrphus_ till the
relations with Acalypterate Muscidae shall be better established.
FAM. 32. SYRPHIDAE (_Hover-flies_).—_Of moderate or rather large size,
frequently spotted or banded with yellow, with a thick fleshy proboscis
capable of being withdrawn into a cleft on the under side of the head;
antennae not placed in definite cavities, three-jointed (usually very
short), and leaving a seta that is not terminal in position, and may be
feathered. Squama variable, never entirely covering the halteres; the chief
(third to fifth) longitudinal veins of the wings connected near their
termination by cross-veins and usually thus forming a sort of short margin
parallel with the hind edge of the wing; a more or less imperfect false
nervure running between the third and fourth longitudinal nervures; no
empodium and generally no distinct system of bristles on the back of the
body._ The Syrphidae (Fig. 212) form one of the largest and best known of
all the families of flies; they abound in our gardens where, in sunny
weather, some species may be nearly always seen hovering over flowers, or
beneath trees in places where the rays of the sun penetrate amidst the
shade. There are two or three thousand species known, so that of course
much variety exists; some are densely covered with hair (certain
_Volucella_ and others), many are of elegant form, and some bear a
{499}considerable resemblance to Hymenoptera of various groups. The
peculiar veining of the wings permits of their easy identification, the
line of two nervules, approximately parallel with the margin of the distal
part of the wing (Fig. 212, D), and followed by a deep bay, being eminently
characteristic, though there are some exceptions; there are a few forms in
which the antennae are exceptional in having a terminal pointed process.
The proboscis, besides the membranous and fleshy lips, consists of a series
of pointed slender lancets, the use of which it is difficult to comprehend,
as the Insects are not known to pierce either animals or vegetables, their
food being chiefly pollen; honey is also doubtless taken by some species,
but the lancet-like organs appear equally ill-adapted for dealing with it.
The larvae are singularly diversified; first, there are the eaters of
Aphidae, or green-fly; some of these may be generally found on our
rose-bushes or on thistles, when they are much covered with Aphids; they
are soft, maggot-like creatures with a great capacity for changing their
shape and with much power of movement, especially of the anterior part of
the body, which is stretched out and moved about to obtain and spear their
prey: some of them are very transparent, so that the movements of the
internal organs and their vivid colours can readily be seen: like so many
other carnivorous Insects, their voracity appears to be insatiable. The
larvae of many of the ordinary Hover-flies are of this kind. _Eristalis_
and its allies are totally different, they live in water saturated with
filth, or with decaying vegetable matter (the writer has found many
hundreds of the larvae of _Myiatropa florea_ in a pool of water standing in
a hollow beech-tree). These rat-tailed maggots are of great interest, but
as they have been described in almost every work on entomology, and as
Professor Miall[422] has recently given an excellent account of their
peculiarities, we need not now discuss them. Some of the flies of the genus
_Eristalis_ are very like honey-bees, and appear in old times to have been
confounded with them; indeed, Osten Sacken thinks this resemblance gave
rise to the "Bugonia myth," a fable of very ancient origin to the effect
that Honey-bees could be procured from filth, or even putrefying carcases,
by the aid of certain proceedings that savoured slightly of witchcraft, and
may therefore have increased the belief of the operator in the
{500}possibility of a favourable result. It was certainly not bees that
were produced from the carcases, but Osten Sacken suggests that
_Eristalis_-flies may have been bred therein.
In the genus _Volucella_ we meet with a third kind of Syrphid larva. These
larvae are pallid, broad and fleshy, surrounded by numerous angular,
somewhat spinose, outgrowths of the body; and have behind a pair of
combined stigmata, in the neighbourhood of which the outgrowths are
somewhat larger; these larvae live in the nests of Bees and Wasps, in which
they are abundant. Some of the _Volucella_, like many other Syrphidae, bear
a considerable resemblance to Bees or Wasps, and this has given rise to a
modern fable about them that appears to have no more legitimate basis of
fact than the ancient Bees-born-of-carcases myth. It was formerly assumed
that the _Volucella_-larvae lived on the larvae of the Bees, and that the
parent flies were providentially endowed with a bee-like appearance that
they might obtain entrance into the Bees' nests without being detected, and
then carry out their nefarious intention of laying eggs that would hatch
into larvae and subsequently destroy the larvae of the Bees. Some
hard-hearted critic remarked that it was easy to understand that providence
should display so great a solicitude for the welfare of the _Volucella_,
but that it was difficult to comprehend how it could be, at the same time,
so totally indifferent to the welfare of the Bees. More recently the tale
has been revived and cited as an instance of the value of deceptive
resemblance resulting from the action of natural selection, without
reference to providence. There are, however, no facts to support any theory
on the subject. Very little indeed is actually known as to the habits of
_Volucella_ in either the larval or imaginal instars; but the little that
is known tends to the view that the presence of the _Volucella_ in the
nests is advantageous to both Fly and Bee. Nicolas has seen _Volucella
zonaria_ enter the nest of a Wasp; it settled at a little distance and
walked in without any fuss being made. Erné has watched the
_Volucella_-larvae in the nests, and he thinks that they eat the waste or
dejections of the larvae. The writer kept under observation
_Volucella_-larvae and portions of the cells of _Bombus_, containing some
larvae and pupae of the Bees and some honey, but the fly-larvae did not
during some weeks touch any of the Bees or honey, and ultimately died,
presumably of starvation. Subsequently, he experimented with
_Volucella_-larvae and a portion {501}of the comb of wasps containing
pupae, and again found that the flies did not attack the Hymenoptera; but
on breaking a pupa of the Wasp in two, the fly-larvae attacked it
immediately and eagerly; so that the evidence goes to show that the
_Volucella_-larvae act as scavengers in the nests of the Hymenoptera.
Künckel d'Herculais has published an elaborate work on the European
_Volucella_; it is remarkable for the beauty of the plates illustrating the
structure, anatomy and development, but throws little direct light on the
natural history of the Insects. _V. bombylans_, one of the most abundant of
our British species, appears in two forms, each of which has a considerable
resemblance to a _Bombus_, and it has been supposed that each of the two
forms is specially connected with the Bee it resembles, but there is no
evidence to support this idea; indeed, there is some little evidence to the
contrary. The genus _Merodon_ has larvae somewhat similar to those of
_Volucella_, but they live in bulbs of _Narcissus_; _M. equestris_ has been
the cause of much loss to the growers of Dutch bulbs; this Fly is
interesting on account of its great variation in colour; it has been
described as a whole series of distinct species.
The most remarkable of the numerous forms of Syrphid larvae are those of
the genus _Microdon_ (Fig. 239), which live in ants' nests. They have no
resemblance to Insect-larvae, and when first discovered were not only
supposed to be little Molluscs, but were actually described as such under
the generic names of _Parmula_ and _Scutelligera_. There is no appearance
of segmentation of the body; the upper surface is covered by a sort of
network formed by curved setae, which help to retain a coating of dirt;
there is no trace externally of any head, but on the under surface there is
a minute fold in which such mouth-organs as may be present are probably
concealed; the sides of the body project so as to form a complex fringing
arrangement; the terminal stigmata are very distinct, the lateral processes
connected with them (the "Knospen" of Dr. Meijere), are, however, very
irregular and placed at some distance from the stigmatic scar. Pupation
occurs by the induration of the external covering and the growth from it,
or rather through it, of two short horns in front. Inside this skin there
is formed a soft pupa, of the kind usual in Cyclorrhaphous flies; the
dehiscence of the external covering is, however, of unusual nature, three
little pieces being {502}separated from the anterior part of the upper
surface, while the lower face remains intact. The account of the pupation
given by Elditt[423] is not complete: the two horns that project are, it
would appear, not portions of the larval skin, but belong to the head of
the pupa, and according to Elditt are used to effect the dehiscence of the
case for the escape of the fly; there does not appear to be any
head-vesicle. Nothing is known as to the details of the life of these
anomalous larvae. M. Poujade has described two species found in France in
the nests of the ant _Lasius niger_.[424] The larva we figure was found by
Colonel Yerbury in nests of an _Atta_ in Portugal, and an almost identical
larva was recently found by Mr. Budgett in Paraguay. The flies themselves
are scarce, _Microdon mutabilis_ (formerly called _M. apiformis_) being one
of the rarest of British flies. They have the antennae longer than is usual
in Syrphidae, and the cross-veins at the outside of the wing are
irregularly placed, so that the contour is very irregular: the resemblance
to bees is very marked, and in some of the South American forms the hind
legs are flattened and hairy like those of bees. The oviposition of
_Microdon_ has been observed by Verhoeff;[425] he noticed that the fly was
frequently driven away by the ants—in this case, _Formica sanguinea_—but
returned undiscouraged to its task.
[Illustration: Fig. 239—Larva of _Microdon_ sp. Portugal. A, Dorsal view of
the larva, × 4; 1, the stigmatic structure; B, posterior view of stigmatic
structure; C, a portion of the marginal fringe of the body.]
A brief résumé of the diverse modes of life of Syrphid larvae has been
given by Perris,[426] and he also gives some information as to the curious
horns of the pupae, but this latter point much {503}wants elucidation.
Whether the Syrphidae, or some of them, possess a ptilinum that helps them
to emerge from the pupa is more than doubtful, though its existence has
been affirmed by several authors of good repute.[427]
[Illustration: Fig. 240.—_Diopsis apicalis._ Natal. A, The fly; B,
extremity of cephalic protuberance, more magnified. _a_, The eye; _b_, the
antenna; C, middle of head, front view; _c_, ocelli.]
SERIES 4. CYCLORRHAPHA SCHIZOPHORA
FAM. 33. MUSCIDAE ACALYPTRATAE.—This group of flies has been the least
studied of all the Diptera; it is generally treated as composed of twenty
or thirty different families distinguished by very slight characters. It
is, however, generally admitted by systematists that these assemblages have
not the value of the families of the other divisions of Diptera, and some
even go so far as to say that they are altogether only equivalent to a
single family. We do not therefore think it necessary to define each one
_seriatim_; we shall merely mention their names, and allude to certain
points of interest connected with them. Taken collectively they may be
defined as very _small flies, with three-jointed antennae (frequently
looking as if only two-jointed), bearing a bristle that is not terminally
placed; frequently either destitute of squamae or having these imperfectly
developed so as not to cover the halteres; and possessing a comparatively
simple system of nervuration, the chief nervures being nearly straight, so
that consequently few cells are formed_. These characters will distinguish
the group {504}from all the other Diptera except from forms of Aschiza, and
from certain Anthomyiidae, with both of which the Acalyptratae are really
intimately connected. Considerable difference of opinion prevails as to the
number of these divisions, but the families usually recognised are:—
1. Doryceridae.
2. Tetanoceridae.
3. Sciomyzidae.
4. Diopsidae.
5. Celyphidae.
6. Sepsidae incl. Piophilidae.
7. Chloropidae (= Oscinidae).
8. Ulidiidae.
9. Platystomidae.
10. Ephydridae.
11. Helomyzidae.
12. Dryomyzidae.
13. Borboridae.
14. Phycodromidae.
15. Thyreophoridae.
16. Scatophagidae. (= Scatomyzidae).
17. Geomyzidae incl. Opomyzidae.
18. Drosophilidae; incl. Asteidae.
19. Psilidae.
20. Tanypezidae (= Micropezidae).
21. Trypetidae.
22. Sapromyzidae incl. Lonchaeidae.
23. Rhopalomeridae.
24. Ortalidae.
25. Agromyzidae incl. Phytomyzidae.
26. Milichiidae.
27. Octhiphilidae.
28. Heteroneuridae.
29. Cordyluridae.
Brauer associates Conopidae with Acalyptrate Muscids, and calls the Group
Holometopa; applying the term Schizometopa to the Calyptrate Muscidae.
No generalisation can yet be made as to the larvae of these divisions,
neither can any characters be pointed out by which they can be
distinguished from the larvae of the following families. In their habits
they have nothing specially distinctive, and may be said to resemble the
Anthomyiidae, vegetable matter being more used as food than animal; many of
them mine in the leaves or stems of plants; in the genus _Dorycera_ the
larva is aquatic, mining in the leaves of water-plants, and in Ephydridae
several kinds of aquatic larvae are found, some of which are said to
resemble the rat-tailed larvae of Syrphidae; certain of these larvae occur
in prodigious quantities in lakes, and the Insects in some of their early
stages serve the Mexicans as food, the eggs being called Ahuatle, the
larvae Pusci, the pupae Koo-chah-bee. Some of the larvae of the Sciomyzidae
are also aquatic: that of _Tetanocera ferruginea_ is said by Dufour to
consist only of eight segments, and to be metapneustic; Brauer considers
the Acalyptrate larvae to be, however, in general, amphipneustic, like
those of Calyptratae. The Chloropidae are a very important family owing to
their occasional excessive multiplication, and to their living on cereals
and other grasses, various parts of which they attack, sometimes causing
great losses to the agriculturist. The species of the genus _Chlorops_ are
{505}famous for the curious habit of entering human habitations in great
swarms: frequently many millions being found in a single apartment.
Instances of this habit have been recorded both in France and England,
Cambridge being perhaps the place where the phenomenon is most persistently
exhibited. In the year 1831 an enormous swarm of _C. lineata_ was found in
the Provost's Lodge at King's College and was recorded by Leonard Jenyns;
in 1870 another swarm occurred in the same house if not in the same
room.[428] Of late years such swarms have occurred in certain apartments in
the Museums (which are not far from King's College), and always in the same
apartments. No clue whatever can be obtained as to their origin; and the
manner in which these flies are guided to a small area in numbers that must
be seen to be believed, is most mysterious. These swarms always occur in
the autumn, and it has been suggested that the individuals are seeking
winter quarters.
[Illustration: Fig. 241—_Celyphus_ (_Paracelyphus_) sp. West Africa. A, The
fly seen from above; _a_, scutellum; _b_, base of wing: B, profile, with
tip of abdomen bent downwards; _a_, scutellum; _b_, _b_, wing; _c_, part of
abdomen.]
Several members of the Acalyptratae have small wings or are wingless, as in
some of our species of _Borborus_. The Diopsidae—none of which are
European—have the sides of the head produced into long horns, at the
extremity of which are placed the eyes and antennae; these curiosities
(Fig. 240) are apparently common in both Hindostan and Africa. In the
horned flies of the genus _Elaphomyia_, parts of the head are prolonged
into horns of very diverse forms according to the species, but bearing on
the whole a great resemblance to miniature stag-horns. A genus
(_Giraffomyia_) with a long neck, and with partially segmented appendages,
instead of horns on the head, has been recently discovered by Dr. Arthur
Willey in New Britain. Equally remarkable are the species of _Celyphus_;
they do not look like flies at all, owing to the scutellum being inflated
and enlarged so as to cover all the posterior parts {506}of the body as in
the Scutellerid Hemiptera: the wings are entirely concealed, and the
abdomen is reduced to a plate, with its orifice beneath, not terminal; the
surface of the body is highly polished and destitute of bristles. Whether
this is a mimetic form, occurring in association with similar-looking Bugs
is not known. The North American genus _Toxotrypana_ is furnished with a
long ovipositor; and in this and in the shape of the body resembles the
parasitic Hymenoptera. This genus was placed by Gerstaecker in Ortalidae,
but is considered by later writers to be a member of the Trypetidae. This
latter family is of considerable extent, and is remarkable amongst the
Diptera for the way in which the wings of many of its members are
ornamented by an elaborate system of spots or marks, varying according to
the species.
FAM. 34. ANTHOMYIIDAE.—_Flies similar in appearance to the House-fly; the
main vein posterior to the middle of the wing (4th longitudinal) continued
straight to the margin, not turned upwards. Eyes of the male frequently
large and contiguous, bristle of antenna either feathery or bare._ This
very large family of flies is one of the most difficult and unattractive of
the Order. Many of its members come close to the Acalyptrate Muscidae from
which they are distinguished by the fact that a well-developed squama
covers the halteres; others come quite as close to the Tachinidae, Muscidae
and Sarcophagidae, but may readily be separated by the simple, not
angulate, main vein of the wing. The larval habits are varied. Many attack
vegetables, produce disintegration in them, thus facilitating
decomposition. _Anthomyia brassicae_ is renowned amongst market gardeners
on account of its destructive habits. _A. cana_, on the contrary, is
beneficial by destroying the migratory Locust _Schistocerca peregrina_; and
in North America, _A. angustifrons_ performs a similar office with
_Caloptenus spretus_. One or two species have been found living in birds;
in one case on the head of a species of _Spermophila_, in another case on a
tumour of the wing of a Woodpecker. _Hylemyia strigosa_, a dung-frequenting
species, has the peculiar habit of producing living larvae, one at a time;
these larvae are so large that it would be supposed they are full grown,
but this is not the case, they are really only in the first stage, an
unusual amount of growth being accomplished in this stadium. _Spilogaster
angelicae_, on the other hand, according to {507}Portschinsky, lays a small
number of very large eggs, and the resulting larvae pass from the first to
the third stage of development, omitting the second stage that is usual in
Eumyiid Muscidae.[429]
[Illustration: Fig. 242—_Ugimyia sericariae._ A, The perfect fly, × 3/2; B,
tracheal chamber of a silkworm, with body of a larva of _Ugimyia_
projecting; _a_, front part of the maggot; _b_, stigmatic orifice of the
maggot; _c_, stigma of the silkworm. (After Sasaki.)]
FAM. 35. TACHINIDAE.—_First posterior cell of wing nearly or quite closed.
Squamae large, covering the halteres: antennal arista bare: upper surface
of body usually bristly._ This is an enormous family of flies, the larvae
of which live parasitically in other living Insects, Lepidopterous larvae
being especially haunted. Many have been reared from the Insects in which
they live, but beyond this little is known of the life-histories, and still
less of the structure of the larvae of the Tachinidae, although these
Insects are of the very first importance in the economy of Nature. The eggs
are usually deposited by the parent-flies near or on the head of the
victim; Riley supposed that the fly buzzes about the victim and deposits an
egg with rapidity, but a circumstantial account given by Weeks[430]
discloses a very different process: the fly he watched sat on a leaf
quietly facing a caterpillar of _Datana_ engaged in feeding at a distance
of rather less than a quarter of an inch. "Seizing a moment when the head
of the larva was likely to remain stationary, the fly stealthily and
rapidly bent her abdomen downward and extended from the last segment what
proved to be an ovipositor. This passed forward beneath her body and
between the legs until it projected beyond and nearly on a level with the
head of the fly and came in contact with the eye of the larva upon which an
egg was deposited," making an addition to five already there. _Ugimyia
sericariae_ does great {508}harm in Japan by attacking the silkworm, and in
the case of this fly the eggs are believed to be introduced into the victim
by being laid on mulberry leaves and swallowed with the food; several
observers agree as to the eggs being laid on the leaves, but the fact that
they are swallowed by the silkworm is not so certain. Sasaki has given an
extremely interesting account of the development of this larva.[431]
According to him, the young larva, after hatching in the alimentary canal,
bores through it, and enters a nerve-ganglion, feeding there for about a
week, after which the necessity for air becoming greater, as usual with
larvae, the maggot leaves the nervous system and enters the tracheal
system, boring into a tube near a stigmatic orifice of the silkworm, where
it forms a chamber for itself by biting portions of the tissues and
fastening them together with saliva. In this it completes its growth,
feeding on the interior of the silkworm with its anterior part, and
breathing through the stigmatic orifice of its host; after this it makes
its exit and buries itself deeply in the ground, where it pupates. The work
of rupturing the puparium by the use of the ptilinum is fully described by
Sasaki, and also the fact that the fly mounts to the surface of the earth
by the aid of this same peculiar air-bladder, which is alternately
contracted and distended. Five, or more, of the _Ugimyia_-maggots may be
found in one caterpillar, but only one of them reaches maturity, and
emerges from the body. The Tachinid flies appear to waste a large
proportion of their eggs by injudicious oviposition; but they make up for
this by the wide circle of their victims, for a single species has been
known to infest Insects of two or three different Orders.
[Illustration: Fig. 243—Diagrammatic section of silkworm to show the habits
of _Ugimyia_. _a_, Young larva; _b_, egg of _Ugimyia_ in stomach of the
silkworm; _c_, larva in a nerve-ganglion; _d_, larva entering a ganglion;
_e_, larva embedded in tracheal chamber, as shown in Fig. 242, B. (After
Sasaki.)]