The Brachycera, from [Greek: brachus], "short;" and [Greek: keras], "a
horn"--these Diptera having short antennæ--are divided into four
groups. In this subdivision the sucker is composed of six bristles.
Amongst other families it includes that of the _Tabanidæ_; the insects
belonging to which family are of remarkable strength, and possessed of
daring and courage in the highest degree. Their wings are provided
with powerful muscles, their feet are very strong, and their trunk is
provided with six flat, sharp lancets. Distributed over the entire
world, their instinct is everywhere the same, it is the desire for
blood, at least in the females; for the males are not so warlike, they
do no harm, but live on the juices of flowers. They are chiefly found
in woods and pastures, and during the hottest part of the day in
summer may be seen flying about seeking for their prey.
M. de Saint-Fargeau has described the manner in which the males fly.
They may be seen flying hither and thither in the glades of woods,
remaining for some time suspended in the air, then darting quickly and
suddenly away a yard or two, again taking up the same immovable
position, and in each of these movements turning the head to the
opposite way from that in which they are going. This naturalist is
certain that on these occasions they are watching for the females,
which they dart upon. When they have succeeded in doing so, they rise
so high as to be out of sight.
To this group belongs the genus _Tabanus_.
The first species we shall mention, _Tabanus autumnalis_ (Fig. 33), a
common species, is eight or nine lines in length, and of blackish
colour. The palpi, the face, and the forehead are grey; the antennæ
black; the thorax grey, striped with brown; the abdomen spotted with
yellow; the legs of a yellowish white; and the outer edge of the wings
brown.
Another species (_Tabanus bovinus_) is twelve lines in length, and of
a blackish brown. The palpi, the face, and the forehead are yellow;
the antennæ black, with a whitish base; the thorax, covered with
yellow hair, is striped with black; the posterior edge of the segments
of the abdomen pale yellow; the legs yellowish, with the extremities
black, and the exterior edge of the wings yellow. This species is
frequently met with in woods.
A third species, _Chrysops cæcutiens_ (Fig. 34), which belongs to the
same family, and of which the generic name _Chrysops_ signifies
golden-eyed, torments horses and cattle very much by biting them round
the eyes. Its thorax is of a yellowish colour, striped or spotted with
black; the abdomen yellow, and the eyes golden.
In the next group of the Brachycera the sucker is composed of four
bristles, and the antennæ generally terminate in a point which appears
to be rather a development than an appendage.
This group includes a number of genera, but the following only possess
sufficient interest to claim our attention. From the _Tanystomæ_ we
select the families of the _Asilidæ_, _Empidæ_, and _Bombylidæ_. As
types of the _Brachystomæ_ we select the _Leptidæ_ and _Syrphidæ_.
[Illustration: Fig. 33.--Tabanus autumnalis.]
[Illustration: Fig. 34.--Chrysops cæcutiens.]
The chief characteristic of the _Asilidæ_ is strength. All their
organs combine to produce this quality, which they display only too
much, being as formidable to cattle as the _Tabani_, but even
surpassing those insects in natural cruelty.
The _Asilidæ_ unceasingly attack other insects, and even those of
their own kind. Their trunk is strong; one of the fibres of the sucker
is furnished with small points, turned back, which are intended to
hold firmly to the body into which it has entered. They carry on their
devastations in the glades of woods and on sunny roads.
We will mention in this group _Asilus crabroniformis_ (Fig. 35), an
insect ten to twelve lines long, having a yellow head, black antennæ,
and thorax of a brownish yellow. The three first segments of the
abdomen are black, the second and third having a white spot on each
side, the remaining segments are yellow. The wings are yellowish,
spotted with black on the inner and hind margin. This species is
common over the whole of Europe, and lives at the expense of
caterpillars and other insects, of which it sucks the blood with the
greatest voracity.
[Illustration: Fig. 35.--Asilus crabroniformis.]
[Illustration: Fig. 36.--Bombylius major.]
The _Empidæ_ live in the same way as the _Asilidæ_, but the males are
chiefly nourished by the juices of flowers.
"They wage war on other insects," says M. Macquart, in his "Histoire
Naturelle des Diptères," "either when flying or running, and they
seize their victims with their feet, which are formed in various ways,
and well adapted for their purpose, but it is in the air that their
hunting, as well as their amours, chiefly take place. They unite
together in numerous companies, which during fine summer evenings
whirl like gnats about the water's edge. A singular observation,
however, that I have made on the _Empis_, is, that among the thousands
of pairs that I have seen resting on hedges and bushes, nearly all the
females were occupied in sucking an insect; some had hold of small
_Phryganeæ_,[13] others of _Ephemeræ_,[14] and the greater part of
_Tipulæ_."
[13] The insects produced from the caddis or case-worm.--ED.
[14] May-fly family.--ED.
The _Empidæ_ have the trunk bent down, and resembling the beak of a
bird; but the _Bombylidæ_, on the contrary, have the trunk extended
straight in front.
The typical genus which has given its name to this latter group is
easily to be recognised by the elegance of the fur which covers its
body, the slenderness of its feet, and the length of its wings, which
extend horizontally on each side of the body.
Much more common in hot climates than in the North, these insects, the
larvæ of which are not yet known, take flight in the middle of the
day, when the sun's rays are hottest. They fly very fast, making a
dull buzzing sound, and hover over flowers, from which they draw the
juices without settling.
Fig. 36 represents the _Bombylius major_, which is common enough
throughout the whole of Europe. This insect is from four to six lines
long, black, with yellow fur; the feet light yellow; and the wings
have the edges bordered with a sinuous brown band.
The genus _Anthrax_, belonging to this family, has a different form to
_Bombylius_. The body is much less hairy; the trunk is short and
concealed in the mouth; the wings, which are very large, are clothed,
at least in the principal genus, in a garb of mourning, sufficiently
remarkable, in which the combinations of black and white are admirably
diversified.
"Here," says M. Macquart, "the line which separates the two colours is
straight; there it represents gradations, in other cases it is deeply
sinuous. Sometimes the dark part shows transparent points, or the
glassy part dark spots. This sombre garb, added to the velvet black of
the body, gives the Anthrax a most elegant appearance; and while
resting on the corolla of the honeysuckle and hawthorn to suck the
juice, forms a most striking contrast, and sets forth its beauty no
less than that of those lovely flowers."
_Anthrax sinuata_ is common in Europe.
The family of the _Syrphidæ_ includes three remarkable types, which we
cannot pass over in silence. They are _Vermileo_, _Volucella_, and
_Helophilus_.
_Vermileo de Geeri_ (Fig. 37), which inhabits the central and southern
parts of France, is four or five lines in length. Its face is white;
its forehead grey, bordered with black; the thorax of a yellowish
grey, with four brown stripes in the male; the abdomen light yellow,
spotted with black; and the wings glassy.
[Illustration: Fig. 37.--Vermileo de Geeri.]
[Illustration: Fig. 38.--A species of Volucella.]
The larva of the _Vermileo_ has a thin cylindrical body, capable of
bending itself in every direction; a conical head, armed with two
horny points; and the last segment elongated, flat, elevated, and
terminated by four hairy tentacles; at the sides of the fifth segment
may be observed a little angle, from which projects a horny retractile
point.
It is of very singular habits. It makes a small tunnel in the sand,
having a conical mouth, where it waits, like the spider, immovable. As
soon as an insect falls into the hole, it raises its head, and
squeezing its prey in the folds of its body, devours it, and
afterwards throws out the skin. It lives in this way for at least
three years before attaining the perfect state.
The _Volucellæ_ (Fig. 38) have a strong resemblance to the humble-bee.
Certain kinds make use and abuse of this resemblance to introduce
themselves fraudulently into its nests, and to deposit their eggs
therein. When these eggs have hatched, the larvæ, which have the mouth
armed with two mandibles, devour the larvæ of their hosts, the bees.
This is the return they make for the hospitality they have received!
[Illustration: Fig. 39.--A species of Helophilus.]
[Illustration: Fig. 40.--Larvæ of a Helophilus.]
The _Helophili_ (Fig. 39) deserve to be mentioned here on account of
the singular form of many of their larvæ. The head is thick, fleshy,
and varying a little in form. But the point by which they are easily
to be distinguished from most other larvæ is, that they have always
very long tails, sometimes, indeed, out of proportion to the length of
the body. Réaumur called these larvæ "vers à queue de rat;" they are
known in England as rat-tailed maggots, and their habits are aquatic.
Having placed some of them in a bason of water, Réaumur saw that they
kept in a perpendicular position at the bottom of the bason and
parallel to one another, the extremities of their tails being on the
surface of the water. He then increased the depth of the water by
degrees; and, as it got deeper, observed that the tail of each worm
became longer. These tails, which at first were only two inches long,
at last attained to five.
It will be remarked that the body of each worm does not exceed five
lines in length. The tail is a peculiar organ, by the aid of which the
worm breathes, although its body may be covered by water to the depth
of several inches. It is composed of two tubes, one of which shuts
into the other, like a telescope. Réaumur calls it the breathing tube.
It terminates in a little brown knob, in which, according to Réaumur,
are two holes for the purpose of receiving the air, and which have
five little tufts of hair, which float on the surface of the water.
When the time comes for the metamorphosis of these worms, they come
out of the water and bury themselves in the earth; the skin then
hardens and becomes a sort of cocoon. In this cocoon the insect loses
the form of a worm, and takes by degrees that of the pupa, which it
keeps until circumstances cause it to throw off its last coverings,
and to appear in the winged state.
What an eventful life! what a life full of changes and turns of
fortune is that of these insects, which pass the first and longest
period of their existence under water, another part of their life
under the ground, and, finally, after having existed in these two
elements, enjoy, high in the air, the pleasures of flight!
The third group of Brachycera is that of the _Dichæta_; that is, those
flies having two-fibred suckers. Among these are classed the
_OEstri_, the _Conopes_, and the flies properly so called.
The genus _OEstrus_, the Gad, Bot-fly, or Breeze, comprises those
formidable insects which attack the horse, the sheep, and the ox.[15]
The labours of Réaumur, in his admirable Memoirs, and those of M.
Joly, Professor of Zoology to the Faculté des Sciences de Toulouse,
who published some most valuable researches on this subject, in 1846,
will guide us in the following brief explanation.
[15] Mr. Bates, in his interesting "Naturalist on the Amazons,"
mentions an _OEstrus_ as occurring in those regions, which
deposits its eggs in the human flesh, the larva causing a
swelling which resembles a boil.--ED.
The following is the description given by M. Joly of the Gad-fly
(_OEstrus equi_) represented in Figs. 41, 42, which are taken from a
drawing which accompanies that naturalist's Memoirs.
The head of this insect is large and obtuse; the face light yellow,
with whitish silky fur; the eyes blackish; the antennæ ferruginous;
the thorax grey; and the abdomen of a reddish yellow, with black
spots. The wings are whitish, not diaphanous, with a golden tint, and
divided by a winding band of blackish colour. The feet are palish
yellow.
[Illustration: I. A Herd of Horses attacked by Gad-flies (_OEstrus
equi_).]
[Illustration: Fig. 41.--Horse-fly, male (_OEstrus_ [_gasterophilus_]
_equi_).]
[Illustration: Fig. 42.--Horse-fly, female (_OEstrus_ [_gasterophilus_]
_equi_).]
This species is found in France, in Italy, and also in the East,
especially in Persia, and rarely in England. During the months of July
and August the _OEstrus_ frequents pastures, and deposits its eggs
chiefly on the shoulders and knees of horses (PLATE I.). In order to
do this, the female suspends herself in the air for some seconds over
the place she has chosen, falls upon it, and with her abdomen bent,
sticks her eggs to the horse's hairs by means of a glutinous liquid
with which they are provided, and which soon dries. This is repeated
at very short intervals. It often happens that from four to five
hundred eggs are thus deposited upon the same horse. Guided by a
marvellous instinct, the female _OEstrus_ generally places her eggs
on those parts of the horse's body which can be most easily touched
with the tongue, that is, at the inner part of the knees, on the
shoulders, and rarely on the outer part of the mane.
[Illustration: Fig. 43.--Eggs of the Gad-fly (_OEstrus_
[_gasterophilus_] _equi_) deposited on the hairs of a horse.]
The eggs of the _OEstrus_, which are white and of conical form,
adhere to the horse's hair, as shown in Fig. 43. They are furnished
with a lid, which at the time of hatching opens, to allow the exit of
the young larva, which takes place, according to M. Joly, about twenty
days after they are deposited. In fact, it is not in the egg state,
but really in that of the larva, that the horse, as we shall explain,
takes into his stomach these parasitical guests, to which Nature has
allotted so singular an abode. When licking itself, the horse carries
them into its mouth, and afterwards swallows them with his food, by
which means they enter the stomach. It is a remarkable fact that it is
sometimes other insects, as the _Tabania_ for instance, that by their
repeated stinging cause the horse to lick himself, and thus to receive
his most cruel enemy. In the perilous journey they have to perform
from the skin of the horse to his stomach, many of the larvæ of the
_OEstrus_, as may be supposed, are destroyed, ground by the teeth of
the animal, or crushed by the alimentary substances. There is hardly
one _OEstrus_ in fifty that arrives safely in the stomach of the
horse; and yet if one were to open a horse which had been attacked by
the _OEstri_, the stomach would be nearly always found to have many
of the larvæ sticking to its inside. Fig. 44, taken from a drawing
which accompanies M. Joly's Memoirs, represents the state of a horse's
stomach attacked by the Gad-fly larvæ.
[Illustration: Fig. 44.--Portion of the stomach of the horse, and
larvæ of OEstrus (gasterophilus) equi.]
The larvæ are of a reddish yellow, and each of their segments is armed
at the posterior edge with a double row of triangular spines, large
and small alternately, yellow at the base, and black at the point,
which is always turned backwards. The head is furnished with two
hooks, which serve to fasten the larva to the internal coats of the
stomach. The spines with which the whole surface of the body is
furnished contribute to fix it more perfectly, preventing the
creatures, by the manner in which they are placed, from being carried
away by the food which has gone through the first process of
digestion.
It is probable that this larva, so singularly deposited, is nourished
by the mucus secreted by the mucous membrane of the stomach, and that
it breathes the air which the horse swallows with its food during the
process of deglutition. It must be acknowledged, however, that it is
in the midst of a gaseous atmosphere which is very unhealthy, for
nearly all the gases generated in the stomach of the horse are fatal
to man and to the generality of animals, as they consist of nitrogen,
carbonic acid, sulphuretted hydrogen, and carburetted hydrogen. To
explain how the insect can live under such circumstances, M. Joly has
suggested the following ingenious hypothesis:--
"When the stomach which the larva inhabits," says this learned
naturalist, "contains only oxygen, or air that is nearly pure, the
insect opens the two lips of the cavity which contains the spiracles,
and breathes at its ease. When the digestion of the alimentary
substance generates gas which is unfit for respiration, or when the
spiracles run the risk of being obstructed by the solid or liquid
substances contained in the stomach, it shuts the lips, and continues
to live on the air contained in its numerous tracheæ."
"Whatever may be the value of this explanation," adds M. Joly, "it is
nevertheless very curious to see an insect pass the greater part of
its life in an atmosphere which would be instantly fatal to most
animals, and in an organ where, under the government of life, chemical
processes bring about the most wonderful changes of the food into the
substance of the animal itself. But how can the insect itself resist
the action of these mysterious powers, and remain alone intact in the
midst of all these matters which are unceasingly changing and
decomposing? This is another question which it is difficult, or rather
impossible, to explain in the present state of science; another enigma
which humbles our pride, and of which He who has created both man and
the worm alone knows the secret."
Arrived at a state of complete development, the larva of the
_OEstrus_ imprisoned in the stomach of the horse leaves the membrane
to which it has been fixed, then directing the anterior part of its
body towards the pyloric opening of the stomach, allows itself to be
carried away with the excrementitious matter. It traverses, mixed with
the excrementary bolus, the whole length of the intestinal canal,
leaves it by the anal orifice, and on touching the ground at once
seeks a suitable place to go through the last but one of its
metamorphoses.
The skin then gets thick, hardens, and becomes black. All the organs
of the animal are composed of a whitish amorphous pulp, which soon
assumes its destined form, and the insect becomes perfect. It then
lifts a lid at the anterior part of its cocoon, emerges, dries its
wings, and flies off.
[Illustration: Fig. 45.--Bot-fly (_OEstrus bovis_).]
The Bot-fly (_OEstrus bovis_, Fig. 45) has a very hairy body, large
head, the face and forehead covered with light yellow hair, the eyes
brown, and the antennæ black. The thorax is yellow, barred with black;
the abdomen of a greyish white at the base, covered with black hair on
the third segment, and the remainder of an orange yellow; the wings
are smoky brown.
As soon as the cattle are attacked, they may be seen, their heads and
necks extended, their tails trembling, and held in a line with the
body, to rush to the nearest river or pond, while such as are not
attacked disperse (PLATE II.). It is asserted that the buzzing alone
of the _OEstrus_ terrifies a bullock to such an extent as to
render it unmanageable. As for the insect, it simply obeys its
maternal instinct, which commands it to deposit its eggs under the
skin of our large ruminants.
[Illustration: II. A Herd of Cattle attacked by Bot-flies (_OEstrus
bovis_).]
Let us now explain how the eggs of the _OEstrus_, deposited in the
skin of the bullock, accommodate themselves to this strange abode. The
mother insect makes a certain number of little wounds in the skin of
the beast, each of which receives an egg, which the heat of the animal
serves to bring forth. It is a natural parallel to the artificial way
which the ancient Egyptians invented of hatching the eggs of domestic
fowls, and which has been imitated badly enough in our day.
Directly the larva of the Bot-fly is out of the egg and lodged between
the skin and the flesh of its host, the bullock, it finds itself in a
place perfectly suitable to its existence. In this happy condition the
larva increases in growth, and eventually becomes a fly in its turn.
Those parts of the animal's body in which the larvæ are lodged are
easily to be recognised, as above each larva may be seen an elevation,
a sort of tumour, termed a bot--a bump, as Réaumur calls it, comparing
it more or less justly to the bump caused on a man's head by a severe
blow.
Fig. 46, taken from a drawing in Réaumur's Memoirs, represents the
bots of which we speak.
The country people are well aware of the nature and cause of these
bots. They know that each one contains a worm, that this worm comes
from a fly, and that later it will be transformed into a fly itself.
Each of these bots has in its interior a cavity, occupied by a larva,
which, as well as the bot, increases in size as the larva becomes
developed.
It is generally on young cows or young bullocks--in fact, on cattle of
from two to three years of age--that these tumours exist, and they are
rarely to be seen on old animals. The fly, which by piercing the skin
occasions these tumours, always chooses those whose skin offers little
resistance. Each tumour is provided with a small opening, by which the
larva breathes.
In order to examine the interior of the cavity, Réaumur opened some of
these tumours, either with a razor or a pair of scissors. He found
them in a most disgusting state. The larva is lodged in a regular
festering wound, matter occupying the bottom of the cavity, and the
head of the worm is continually, or almost continually, plunged in
this liquid. "It is most likely very well off there," says Réaumur;
and he adds that this matter appears to be the sole food of the
larva.
"The position of a horned beast," observes the great naturalist,
"which has thirty or forty of these bumps on its back, would be a very
cruel one, and a terrible state of suffering, if his flesh were
continually mangled by thirty or forty large worms. But it is probable
they cause no suffering, or at least very little, to the large animal.
Besides," continues Réaumur, "those cattle whose bodies are the most
covered with bumps, not only show no signs of pain, but it does not
appear that they are prejudicial to them in any way."
[Illustration: Fig. 46.--Bumps produced on Cattle by the larvæ of the
Bot-fly.]
Réaumur tried to discover how the larva, when arrived at its full
growth, succeeds in leaving its abode, as the opening is smaller than
its own body.
"Nature," says Réaumur, "has taught this worm the surest, the
gentlest, and the most simple of methods, the one to which surgeons
often have recourse to hold wounds open, or to enlarge them. They
press _tents_ into a wound they wish to enlarge. Two or three days
before the worm wishes to come out, it commences to make use of its
posterior part as a tent, to increase the size of its exit from its
habitation. It thrusts it into the hole and draws it out again many
times in the course of two or three days, and the oftener this is
repeated, the longer it is able to retain its posterior end in the
opening, as the hole becomes larger. On the day preceding that on
which the worm is to come out, the posterior part is to be found
almost continually in the hole. At last, it comes out backwards, and
falls to the ground, when it gets under a stone, or buries itself in
the turf; remaining quiet and preparing for its last transformation.
Its skin hardens, the rings disappear, and it becomes black.
Thenceforth the insect is detached from the outer skin, which forms a
cocoon, or box. At the front and upper part of the cocoon is a
triangular piece, which the fly gets rid of when it is in a fit state
to come into the open air."
Fig. 47, taken from drawings in Réaumur's Memoirs, represents the
imago of the _OEstrus_ leaving the cocoon.
[Illustration: Fig. 47.--Imago of Bot-fly emerging.]
[Illustration: Fig. 48.--Ovipositor of the Bot-fly (_OEstrus bovis_).]
The reader is, most likely, desirous to know with the aid of what
instrument the _OEstrus_ is able to pierce the thick skin of the ox.
The female only is possessed of this instrument, which is situated in
the posterior extremity of the body. It is of a shiny blackish brown
colour, and as it were covered with scales. By pressing the abdomen of
the fly between one's two fingers it is thrust out. Réaumur observed
that it was formed of four tubes, which could be drawn the one into
the other, like the tubes of a telescope (Fig. 48). The last of these
appears to terminate in five small scaly knobs, which are not placed
on the same line, but are the ends of five different parts. Three of
these knobs are furnished with points, which form an instrument well
fitted to operate upon a hard thick skin. United together, they form a
cavity similar to that of an auger, and terminating in the form of a
spoon.
The Gad-fly, or Breeze-fly of the sheep, _OEstrus_ (_Cephalemyia
ovis_), has obtained notoriety on account of its attacking those
animals.
Even at the sight of this insect the sheep feels the greatest terror.
As soon as one of them appears, the flock becomes disturbed, the sheep
that is attacked shakes its head when it feels the fly on its nostril,
and at the same time strikes the ground violently with its fore-feet;
it then commences to run here and there, holding its nose near the
ground, smelling the grass, and looking about anxiously to see if it
is still pursued.
[Illustration: Fig. 49.--Cephalemyia ovis.]
It is to avoid the attacks of the _Cephalemyia_ that during the hot
days of summer sheep lie down with their nostrils buried in dusty
ruts, or stand up with their heads lowered between their fore-legs,
and their noses nearly in contact with the ground. When these poor
beasts are in the open country, they are observed assembled with their
nostrils against each other and very near the ground, so that those
which occupy the outside are alone exposed (PLATE III.). The
_Cephalemyia ovis_ (Fig. 49) has a less hairy head, but larger in
proportion to the size of its body than the Gad-fly (_Gasterophilus
equi_). Its face is reddish; its forehead brown with purple bars; its
eyes of a dark and changing green; its antennæ black, its thorax
sometimes grey, sometimes brown, bristling with small black
tubercles; the abdomen white, spotted with brown or black; and the
wings hyaline.
[Illustration: III. Sheep attacked by _Cephalemyia ovis_.]
The _Cephalemyia_ (_OEstrus_) _ovis_ is to be found in Europe,
Arabia, Persia, and in the East Indies. It lays its eggs on the edges
of the animal's nostrils, and the larva lives in the frontal and
maxillary sinuses. It is a whitish worm, having a black transverse
band on each of its segments. Its head is armed with two horny black
hooks, parallel, and capable of being moved up and down and laterally.
Underneath, each segment of the body has several rows of tubercles of
nearly spherical form, surmounted by small bristles having reddish
points, and all of them bent backwards. "These points," says M. Joly,
"probably serve to facilitate the progress of the animal on the smooth
and slippery surfaces of the mucous membranes to which it fixes itself
to feed, and perhaps also to increase the secretion of these membranes
by the irritation occasioned by the bristles with which they are
furnished."[16]
[16] "Recherches sur les OEstrides en général, et
particulièrement sur les OEstres qui attaquent l'homme, le
cheval, le boeuf, et le mouton." Par N. Joly, Professeur à la
Faculté des Sciences de Toulouse. P. 63. Lyons, 1846.
Fixed by means of these hooks to the mucous membrane, which it
perforates, the larva nourishes itself with mucus, and lives in this
state, according to M. Joly, during nearly a whole year. At the end of
this time it comes out, following the same course by which it entered,
falls to the ground, and burying itself to the depth of a few inches,
is transformed into a pupa. The cocoon is of a fine black colour.
Thirty or forty days after its burial it emerges in the perfect state,
and detaching the lid at the anterior end of the cocoon by the aid of
its head, which has increased considerably in size, takes flight.
[Illustration: Fig. 50.--Conops.]
Notwithstanding the formidable appearance of their trunks, the habits
of the perfect _Conopes_ (Fig. 50) are very quiet. In the adult state
they are only to be seen on flowers, of which they suck the honeyed
juice. But with their larvæ the case is otherwise. These latter live
as parasites on the humble-bees (_Bombi_). Latreille saw the _Conops
rufipes_ issue in the perfect state from the body of a humble-bee,
through the intervals of the segments of the abdomen.
The _Mucides_ form that great tribe of Diptera commonly known as
flies, and which are distributed in such abundance over the whole
world. Faithful companions of plants, the flies follow them to the
utmost limits of vegetation. At the same time they are called upon by
Nature to hasten the dissolution of dead bodies. They place their eggs
in the carcases of animals, and the larvæ prey upon the corrupt flesh,
thus quickly ridding the earth of those fatal causes of infection to
its inhabitants. The organs of these insects are also infinitely
modified, in order to adapt them to their various functions.
[Illustration: Fig. 51.--Echinomyia grossa.]
M. Macquart divides the _Muscides_ into three sections--the
_Creophili_, the _Anthomyzides_, and the _Acalyptera_.
The _Creophili_ have the strongest organisation; their movements and
their flight are rapid. The greater part feed on the juices of
flowers, some on the blood or the humours of animals. Some deposit
their eggs on different kinds of insects, others on bodies in a state
of decomposition, some again are viviparous. The insects of the genus
_Echinomyia_, for instance (Fig. 51), derive their nourishment from
flowers. They deposit their eggs on caterpillars, and the young larvæ
on hatching penetrate their bodies and feed on their viscera. How
surprised, sometimes, is the naturalist, who, after carefully
preserving a chrysalis, and awaiting day by day the appearance of the
beautiful butterfly of which it is the coarse and mysterious envelope,
sees a cloud of flies emerge in place of it!
But there is another singular manoeuvre performed by some of the
species of the Diptera with which we are at present occupied to
prepare an abundant supply of provision for their larvæ as soon as
they are hatched. The following are the means they employ. It is well
known that certain fossorial Hymenoptera carry their prey--other
insects which they have caught, weevils, flies, &c., and which they
intend should serve as food for their own larvæ--into their
subterranean abodes. These Diptera, spying a favourable moment, slip
furtively into their retreats, and deposit their eggs on the very food
which was intended for others. Their larvæ, which are soon hatched,
make great havoc among the provisions gathered together in the cave,
and cause the legitimate proprietors to die of starvation.
"This instinct," says M. Macquart, "is accompanied by the greatest
agility, obstinacy, and audacity, which are necessary to carry on this
brigandage; and, on the other hand, the Hymenoptera, seized with fear,
or stupefied, offer no resistance to their enemies, and although they
carry on a continual war against different insects, and particularly
against different _Muscides_, they never seize those of whom they have
so much to complain, and which, nevertheless, have no arms to oppose
them with."
The _Sarcophagæ_ are a very common family of Diptera, and are chiefly
to be found on flowers, from which they steal the juice. The females
do not lay eggs, but are viviparous.
Réaumur, with his usual care, observed this remarkable instance of
viviparism proved in a fly, which seeks those parts of our houses
where meat is kept to deposit its larvæ. This fly is grey, its legs
are black, and its eyes red.
When one of them is taken and held between the fingers, there may
often be seen a small, oblong, whitish, cylindrical worm come out of
the posterior part of the body, and shake itself in order to disengage
itself thoroughly. It has no sooner freed itself than the head of
another begins to show. Thirty or forty sometimes come out in this
manner, and, on pressing the abdomen of the fly slightly, more than
eighty of these larvæ may sometimes be made to come out in a short
space of time. If a piece of meat be put near these worms, they
quickly get into it, and eat greedily. They grow rapidly, attaining
their full size in a few days, and make a cocoon of their skin, from
which in a certain time the imago issues. If the body of one of these
ovo-viviparous flies (for the eggs hatch within the parent) be opened,
a sort of thick ribbon of spiral form is soon seen. This ribbon
appears at first sight to be nothing but an assemblage of worms,
placed alongside of and parallel to one another.
Each worm has a thin white membranous envelope, similar to those
light spiders' webs which float about in autumn, which the French call
_fils de la vierge_, and we denominate _gossamer_.
The fecundity of this fly is very great, for, in the length of a
quarter of an inch, the envelope in which these small worms are
enclosed contains 2,000 of them. Therefore this ribbon, being two
inches and a half long, contains about 20,000 worms.
The members of the genus _Stomoxys_, though nearly related to the
house-fly, differ from it very much in habits. They live on the blood
of animals. The _Stomoxys calcitrans_ is very common in these
climates. Its palpi are tawny yellow, antennæ black, thorax striped
with black, abdomen spotted with brown, and its trunk hard, thin, and
long. It deposits its eggs on the carcases of large animals.
The Golden Fly, _Lucilia Cæsar_, lays its eggs on cut-up meat, or on
dead animals. It is only three or four lines in length, of a golden
green, with the palpi ferruginous, antennæ brown, and feet black.
[Illustration: Fig. 52.--Lucilia hominivorax.]
A species of this genus, the _Lucilia hominivorax_, has lately
obtained a melancholy notoriety. We are indebted to M. Charles
Coquerel, surgeon in the French Imperial navy, for the most exact
information concerning this dangerous Dipteron, and the revelation of
the dangers to which man is liable in certain parts of the globe. But
let us first describe the insect, which is very pretty and of
brilliant colours.
Fig. 52, taken from M. Charles Coquerel's Memoir, represents the larva
and the perfect insect, as well as the horny mandibles with which the
larva is provided. It is rather more than the third of an inch in
length, the head is large, downy, and of a golden yellow. The thorax
is dark blue and very brilliant, with reflections of purple, as is
also the abdomen. The wings are transparent, and have rather the
appearance of being smoked; their margins, as well as the feet, are
black.
This beautiful insect is an assassin. M. Coquerel has informed us that
it sometimes occasions the death of those wretched convicts whom human
justice has transported to the distant penitentiary of Cayenne.
When one of these degraded beings, who live in a state of sordid
filth, goes to sleep, a prey to intoxication, it happens sometimes
that this fly gets into his mouth and nostrils; it lays its eggs
there, and when they are changed into larvæ, the death of the victim
generally follows.[17]
[17] "The majority of convicts attacked by the _Lucilia
hominivorax_," says M. F. Bouyer, captain of the frigate, in
"Un Voyage à la Guyane Française," "have succumbed, despite the
assistance of science. Cures have been the exception: in a
dozen cases three or four are reported."--_Tour du Monde, 1866,
1er Semestre_, p. 318.
These larvæ are of an opaque white colour, a little over half an inch
in length, and have eleven segments. They are lodged in the interior
of the nasal orifices and the frontal sinuses, and their mouths are
armed with two very sharp horny mandibles. They have been known to
reach the ball of the eye, and to gangrene the eyelids. They enter the
mouth, corrode and devour the gums and the entrance of the throat, so
as to transform those parts into a mass of putrid flesh, a heap of
corruption.
Let us turn away from this horrible description, and observe that this
hominivorous fly is not, properly speaking, a parasite of man, as it
only attacks him accidentally, as it would attack any animal that was
in a daily state of uncleanliness.
In many works on medicine may be found mentioned a circumstance which
occurred twenty years ago, at the surgery of M. J. Cloquet. The story
is perhaps not very agreeable, but is so interesting as regards the
subject with which we are occupied, that we think it ought to be
repeated here. One day a poor wretch, half dead, was brought to the
Hôtel-Dieu. He was a beggar, who, having some tainted meat in his
wallet, had gone to sleep in the sun under a tree. He must have slept
long, as the flies had time enough to deposit their eggs on the
tainted meat, and the larvæ time enough to be hatched, and to devour
the beggar's meat. It seems that the larvæ enjoyed the repast, for
they passed from the dead meat to the living flesh, and after
devouring the meat they commenced to eat the owner. Awoke by the
pain, the beggar was taken to the Hôtel-Dieu, where he expired.
Who would suppose that one of the causes which render the centre of
Africa difficult to be explored is a fly not larger than the
house-fly? The Tsetse fly (Fig. 53) is of brown colour, with a few
transverse yellow stripes across the abdomen, and with wings longer
than its body. It is not dangerous to man, to any wild animals, or to
the pig, the mule, the ass, or the goat. But it stings mortally the
ox, the horse, the sheep, and the dog, and renders the countries of
Central Africa uninhabitable for those valuable animals. It seems to
possess very sharp sight. "It darts from the top of a bush as quick as
an arrow on the object it wishes to attack," writes a traveller, M. de
Castelnau.
[Illustration: Fig. 53.--The Tsetse Fly (_Glossina morsitans_).]
Mr. Chapman, one of the travellers who have advanced the farthest into
the middle of Southern Africa, relates that he covered his body with
the greatest care to avoid the bites of this nimble enemy; but if a
thorn happened to make a nearly imperceptible hole in his clothing, he
often saw the Tsetse, who appeared to know that it could not penetrate
the cloth, dart forward and bite him on the uncovered part. The
sucker of blood secretes--in a gland placed at the base of his
trunk--so subtle a poison, that three or four flies are sufficient to
kill an ox.
The _Glossina morsitans_ abounds on the banks of the African river,
the Zambesi, frequenting the bushes and reeds that border it. It
likes, indeed, all aquatic situations. The African cattle recognise at
great distances the buzzing of this sanguinary enemy, and this fatal
sound causes them to feel the greatest fear.
Livingstone, the celebrated traveller, in crossing those regions of
Africa that are watered by the Zambesi, lost forty-three magnificent
oxen by the bites of the Tsetse fly, notwithstanding that they were
carefully watched, and had been very little bitten.
"A most remarkable feature in the bite of the Tsetse is its perfect
harmlessness in man and wild animals, and even calves so long as they
continue to suck the cows. We never experienced the slightest injury
from them ourselves personally, although we lived two months in their
habitat, which was in this case as sharply defined as in many others,
for the south bank of the Chobe was infested by them, and the northern
bank, where our cattle were placed, only fifty yards distant,
contained not a single specimen. This was the more remarkable, as we
often saw natives carrying over raw meat to the opposite bank with
many Tsetses settled on it.
"The poison does not seem to be injected by a sting, or by ova placed
beneath the skin, for, when one is allowed to feed freely on the hand,
it is seen to insert the middle prong of three portions, into which
the proboscis divides, somewhat deeply, into the true skin. It then
draws it out a little way, and it assumes a crimson colour, as the
mandibles come into brisk operation. The previously-shrunken belly
swells out, and, if left undisturbed, the fly quietly departs when it
is full. A slight itching irritation follows, but not more than in the
bite of the mosquito. In the ox this same bite produces no more
immediate effects than in man. It does not startle him, as the gad-fly
does; but a few days afterwards the following symptoms supervene: the
eyes and nose begin to run, the coat stares as if the animal were
cold, a swelling appears under the jaw, and sometimes on the navel;
and, though the animal continues to graze, emaciation commences,
accompanied with a peculiar flaccidity of the muscles, and this
proceeds unchecked until, perhaps months afterwards, purging comes on,
and the animal, no longer able to graze, perishes in the state of
extreme exhaustion. Those which are in good condition often perish,
soon after the bite is inflicted, with staggering and blindness, as if
the brain were affected by it. Sudden changes of temperature produced
by falls of rain seem to hasten the progress of the complaint; but in
general the emaciation goes on uninterruptedly for months, and, do
what we will, the poor animals perish miserably.
"When opened, the cellular tissue on the surface of the body beneath
the skin is seen to be injected with air, as if a quantity of soap
bubbles were scattered over it, or a dishonest awkward butcher had
been trying to make it look fat. The fat is of a greenish-yellow
colour, and of an oily consistence. All the muscles are flabby, and
the heart often so soft that the fingers may be made to meet through
it. The lungs and liver partake of the disease. The stomach and bowels
are pale and empty, and the gall-bladder is distended with bile. These
symptoms seem to indicate, what is probably the case, a poison in the
blood; the germ of which enters when the proboscis is inserted to draw
blood. The poison-germ contained in a bulb at the root of the
proboscis, seems capable, although very minute in quantity, of
reproducing itself. The blood after death by Tsetse is very small in
quantity, and scarcely stains the hands in dissection....
"The mule, ass, and goat enjoy the same immunity from the Tsetse as
man and game. Many large tribes on the Zambesi can keep no domestic
animals except the goat, in consequence of the scourge existing in
their country. Our children were frequently bitten, yet suffered no
harm; and we saw around us numbers of zebras, buffaloes, pigs, pallahs
and other antelopes, feeding quietly in the very habitat of the
Tsetse, yet as undisturbed by its bite as oxen are when they first
receive the fatal poison. There is not so much difference in the
natures of the horse and zebra, the buffalo and ox, the sheep and the
antelope, as to afford any satisfactory explanation of the phenomenon.
Is a man not as much a domestic animal as a dog?
"The curious feature in the case, that dogs perish though fed on milk,
whereas the calves escape so long as they continue sucking, made us
imagine that the mischief might be produced by some plant in the
locality, and not by Tsetse; but Major Vardon, of the Madras army,
settled that point by riding a horse up to a small hill infested by
the insect, without allowing him time to graze, and though he only
remained long enough to take a view of the country and catch some
specimens of Tsetse on the animal, in ten days afterwards the horse
was dead."[18]
[18] "Missionary Travels and Researches in South Africa," by
David Livingstone, LL.D., D.C.L. P. 81, _et seq._ London, John
Murray, 1857. (The extract in the original of this work is from
a French translation: "Explorations dans l'Intérieur de
l'Afrique australe, et voyages à travers le continent
Sainte-Paul de Loanda à l'Embouchure du Zambèze, de 1840 à
1846, traduit de l'Anglais." Pages 93-95. 8vo. Paris,
1859.--ED.)
The inhabitants of the Zambesi can, therefore, have no domestic animal
but the goat. When herds of cattle driven by travellers or dealers are
obliged to cross these regions, they only move them during the bright
nights of the cool season, and are careful to smear them with dung
mixed with milk; the Tsetse fly having an intense antipathy to the
dung of animals, besides being in this season rendered dormant by the
lowness of the temperature. It is only by such precautions that they
are able to get through this dangerous stage of their journey.
The large blue Meat-fly, the familiar representative of the genus
_Calliphora_, is known to all by its brilliant blue and white
reflecting abdomen. This fly, which is common everywhere, is the
_Calliphora vomitoria_ on which Réaumur has made many beautiful
observations, which we will make known to our readers.
[Illustration: Fig. 54.--Eggs of the Meat-fly (_Calliphora vomitoria_).]
If we shut up a blue meat-fly in a glass vase, as Réaumur did, and
place near the insect a piece of fresh meat, before half a day is
passed, the fly will have deposited its eggs thereon one after the
other, in irregular heaps, of various sizes. The whole of these heaps
consist of about two hundred eggs, which are of an iridescent white
colour, and four or five times as long as they are broad. In less than
twenty-four hours after the egg is laid the larvæ is hatched. It is no
sooner born than it thinks of feeding, and buries itself in the meat
with the aid of the hooks and lancets with which it is provided.
These worms do not appear to discharge any solid excrement, but they
produce a sticky liquid, which keeps the meat in a moist state and
hastens its putrefaction. The larvæ eat voraciously and continually;
so much so, that in four or five days they arrive at their full
growth. They then take no more nourishment until they are transformed
into flies. They are now about to assume the pupa state. In this
condition it is no longer necessary for them to remain on the tainted
meat, which has been alike their cradle and their larder, and where
until now they were so well off. They therefore leave it and seek a
retreat under ground.
The larva then assumes a globular form and reddish colour, loses all
motion, and cannot any longer either lengthen or shorten, or dilate or
contract itself. Life seems to have left it. "It would be considered a
miracle," says Réaumur, "if we were told there was any kind of
quadruped of the size of a bear, or of an ox, which at a certain time
of the year, the beginning of winter for instance, disengages itself
completely from its skin, of which it makes a box of an oval form;
that it shuts itself up in this box; that it knows how to close it in
every part, and besides that it knows how to strengthen it in such a
manner as to preserve itself from the effects of the air and the
attacks of other animals. This prodigy is presented to us, on a small
scale, in the metamorphosis of our larva. It casts its skin to make
itself a strong and well-closed dwelling."
If one opens these cocoons only twenty-four hours after the
metamorphoses of the worms, no vestige of those parts appertaining to
a pupa is to be found. But four or five days afterwards, the cocoon is
occupied by a white pupa, provided with all the parts of a fly. The
legs and wings, although enclosed in sheaths, are very distinct; these
sheaths being so thin that they do not conceal them. The trunk of the
fly rests on the thorax; one can discern its lips, and the case which
encloses the lancet. The head is large and well formed, its large,
compound eyes being very distinct. The wings appear still unformed,
because they are folded, and, as it were, packed up. It is a fly, but
an immovable and inanimate fly; it is like a mummy enveloped in its
cloths.
Nevertheless, it is intended this mummy should awake, and when the
time comes it will be strong and vigorous. Indeed, it has need of
strength and vigour to accomplish the important work of its life.
Although its coverings are thin, it is a considerable work for the
insect to emerge, for each of its exterior parts is enclosed in them
as in a case, much the same as a glove fits tightly to all the fingers
of the hand. But that for which the most strength is necessary is the
operation of forming the opening of the cocoon, in which as a mummy it
is so tightly enclosed.
The fly always comes out at the same end of the cocoon, that is, at
the end where its head is placed, and also where the head of the larva
previously was. This end is composed of two parts--of two half cups
placed one against the other. These can be detached from each other
and from the rest of the cocoon. It is sufficient for the fly that one
can be detached, and in order to effect this, it employs a most
astonishing means. It expands and contracts its head alternately, as
if by dilatation; and thus pushes the two half cups away from the end
of the cocoon. This is not long able to resist the battering of the
fly's head, and the insect at length comes out triumphant. This fly,
which should be blue, is then grey; it, however, comes quickly to
perfection, at the end of three hours attaining its ultimate colour;
and in a very short space of time every part of the animal becomes of
that firmness and consistency which characterises them. At the same
time, the wings, which at the moment it came into the world were only
stumps, extend and unfold themselves by degrees. The meat-fly is
represented below (Fig. 55).
One of the features in the formation of this fly which most attracted
the attention of Réaumur, and which is likely to excite the curiosity
of all those who take an interest in insects, is the composition of
its trunk. We will, therefore, with that illustrious observer, take a
glimpse at the remarkable and complicated apparatus by the aid of
which the fly can suck up liquids, and can even taste solid and
crystalline substances, such as sugar.
[Illustration: Fig. 55.--Blue-bottle fly (_Calliphora vomitoria_),
magnified.]
It is no difficult matter to make a fly show its trunk extended to its
full extent. One has only to press between the finger and thumb either
the two sides of the upper and under part of the thorax. It is thus
forced at once to put out its tongue.
[Illustration: Fig. 56.--Trunk of the Meat-fly.]
[Illustration: Fig. 57.--Conical part of the trunk.]
The trunk appears to be composed of two parts joined together, and
forming a more or less obtuse angle (Fig. 56). The first portion of
the trunk, that which joins the head, is perfectly membranous and in
the form of a funnel. We will call it the conical part, and show it
separately (Fig. 57). The second portion terminates in a thick mass,
in part cartilaginous or scaly, and of a shiny brown colour. Above
the conical portion are two oblong antennæ, without joints, of
chestnut colour, and furnished with hairs.
On ceasing to press the thorax, the membranous conical portion may be
seen to draw itself back within its sheath (Fig. 58). The second
portion is at the same time drawn into the cavity, but it raises
itself by forming a more and more acute angle, so that when it reaches
the opening of the cell it is parallel with, and its length is equal
to that of the cell, which is quite large enough to receive it. The
base lengthens and flattens a little, and conceals the trunk.
[Illustration: Fig. 58.--Retractile proboscis of Blue-bottle fly.]
[Illustration: Fig. 59.--Extremity on the proboscis of a fly.]
Let us cause the trunk to extend itself a second time, in order to
observe its tip minutely. Here the opening is placed, which may be
looked upon as the mouth of the insect, and is provided with two large
thick lips (Fig. 59). These lips form a disc, perpendicular to the
axis of the trunk; the disc is oval, and is divided into two equal and
similar parts by a slit. The lips have each a considerable number of
parallel channels situated perpendicularly to the slit. These channels
are formed by a succession of vessels placed near each other. On
pressing the trunk we see that these vessels are distended by a
liquid. Réaumur, from whom we borrow these details, discovered a few
of the uses to which this trunk is applied. He covered the interior of
a transparent glass vase with a light coat of thick syrup. He then put
in some flies, when it was easy to see some of them proceed to fix
themselves to the sides of the vase, and regale themselves on the
sugary liquid, of which they are very fond. He observed them
carefully, and in his admirable work he recommends those who are
curious to try the experiment, with which, like himself, they will
certainly be satisfied.
While the body of the trunk is stationary its end is much agitated. It
may be seen to move in different ways, and with an astonishing
quickness; the lips acting in a hundred different ways, and always
with great rapidity. The small diameter of the disc which they form
lengthens and shortens alternately; the angle formed by the two lips
varies every instant; they become successively flat and convex, either
entirely or partly. All these movements, Réaumur remarks, give a high
idea of the organisation of the part which performs them.
The object of all these movements is to draw the syrup into the
interior of the trunk. If we observe the lips (Fig. 60) attentively,
it will easily be seen that they touch each other about the centre of
the disc, and leave two openings, one in front, the other at the back.
The one in front is, one may say, the mouth of the fly, as it is to
this opening that the liquid is brought, which is intended to be and
is soon introduced into the trunk. Without occupying ourselves for the
present with the channel through which it rises, we may first ask,
whatever that channel may be, what is the power that forces the liquid
into it?
[Illustration: Fig. 60.--Lips of the proboscis of a fly.]
It is nearly certain that suction is the principal cause of the liquid
flowing up the trunk. It would thus be a sort of pump, into which the
liquid is forced by the pressure of the external air. The fly exhausts
the air from the tube of its trunk, and the drop of liquid which is at
the opening penetrates and goes up this channel through the influence
of the atmospheric pressure. To this physical phenomenon must be added
the numerous and multiplied movements which take place in the trunk,
and which are intended to cause sufficient pressure to drive the
liquor which is introduced into the channel upwards.
Réaumur wished to know how it was that very thick syrups, and even
solid sugar, can be sucked up by the soft trunk of the fly. What he
saw is wonderful. If a fly meets with too thick a syrup, it can render
it sufficiently liquid; if the sugar is too hard, it can dissolve
small portions of it. In fact, there exists in its body a supply of
liquid, of which it discharges a drop from the end of its trunk at
will, and lets this fall on the sugar which it wishes to dissolve, or
on the syrup it wishes to dilute. A fly, when held between the
fingers, often shows at the end of its trunk a drop, very fluid and
transparent, of this liquid. "The water poured on the syrup," says
Réaumur, "would not always insinuate itself sufficiently quick into
every part of it; the movement of the fly's lips hastens the
operation; the lips turn over, work, and knead it, so that the water
can quickly penetrate it, in the same way as one handles and kneads
with one's hands a hard paste which it is wished to soften, by causing
the water by which it is covered to mix with it. This, again, is the
same means the fly employs with sugar. When the trunk is forced to
act upon a grain of irregular and rugged form, on which it cannot
easily fasten, its end distorts itself to seize and hold it. It is
sometimes very amusing to see how the fly turns over the grain of
sugar in different ways; it appears to play with it as a monkey would
with an apple. It is, however, only that it may hold it well in order
to moisten it more successfully, and afterwards to pump up the water
which has partly dissolved it."
Réaumur often observed a drop of water at the end of the trunks of
flies which were perfectly surfeited with food. This drop ascended the
trunk, then re-descended to the end, and this many times in
succession. It appeared to him that it was necessary for these
insects, as for many quadrupeds, to chew the cud, as it were; that, in
order the better to digest the liquid they had passed into their
stomachs, they were obliged to bring it back into the trunk that it
might return again better prepared.
In order to assure himself directly of the reality of his supposition,
Réaumur tested the water which a fly, that he says "had got drunk on
sugar," had brought back to the end of its trunk; he found this to be
sugar and water. Also, having given a fly currant-jelly, he observed,
after it had sufficiently gorged itself, several drops of red liquid
in its trunk, and having tasted it, found it had the flavour which,
from its appearance, he guessed it would have.
The illustrious observer, who had already made all these discoveries
on the formation and functions of the trunks of insects, often
reflected on the fact that the liquors of which flies are most fond
are enclosed under the skin of certain fruits, such as pears, plums,
grapes, &c., or even under the skin of some animals of which they suck
the blood. In order that the trunk of a fly may act under such
circumstances, it is necessary for it to pierce and open the skin. If
this is the case, flies ought to be possessed of a lancet. He looked a
long time for this lancet, and at last found it. It is situated on the
upper side of the part of the trunk which is terminated by the lips;
it is placed in a fleshy groove, and is enclosed in a case. It has a
very fine point, and is of light colour (Fig. 61). The point is
situated in the opening which is to be seen between the lips of the
trunk, at its anterior end, through which liquids may pass. That is
the only opening of the lips; and the sucker which takes up the liquid
is the same part which we just now called the case of the lancet.
Réaumur is so interesting an author that it is difficult to cease
quoting him; but we must continue our review of the principal kinds of
Diptera.
The genus _Musca_ (fly), in which Linnæus comprised the immense series
of Diptera, with the exception of the _Tipulidæ_, the _Tabanidæ_, the
_Asilidæ_, the _Bombylidæ_, and the _Empidæ_, is now reduced to the
House Fly and a few resembling it. The habits of these troublesome
companions are in conformity with the two great principles of animal
life, that is, eating and propagating their species.
Flies feed principally on fluids which exude from the bodies of
animals; that is, sweat, saliva, and other secretions. They also seek
vegetable juices; and they may be seen in our houses to feed eagerly
on fruits and sweet substances.
[Illustration: Fig. 61.--Lancet of the Meat Fly.]
[Illustration: Fig. 62.--House Fly (_Musca domestica_).]
The common flies deposit their eggs on vegetables, and particularly on
fungi in a state of decomposition, on dung-heaps, cow dung, &c. They
are essentially parasites, settling on both man and beast, to suck up
the fluid substances which are diffused over the surface of their
bodies. In our dwellings they eat anything that will serve to nourish
them. Generation succeeds generation with the greatest rapidity.
The House Fly (_Musca domestica_, Fig. 62) is about three lines in
length, ash coloured, with the face black, the sides of the head
yellow, and the forehead yellow with black stripes; the thorax is
marked with black lines; the abdomen is pale underneath, and a
transparent yellow at the sides, in the males, and is speckled with
black. The feet are black; the wings transparent, and yellowish at the
base. This species is extremely plentiful throughout the whole of
Europe. Every one knows how annoying it is towards the end of the
summer, and especially so in the South of France during the hot
season.
The Ox Fly (_Musca bovina_), a near relation of the house fly, is also
very common. It settles on the nostrils, the eyes, and the wounds of
animals.
The Executioner Fly (_Musca carnifex_), which is not rare in France,
also attacks oxen. It is of a dark metallic green colour with a
slight ash-coloured down. Its forehead is silvery at the front and
sides; the abdomen is edged with black; the wings hyaline, and yellow
at the base.
_Section of the Anthomyides._--The section of _Anthomyides_ comprises
insects which appear to be _Creophili_ whose organisation has become
weakened by almost insensible degrees. Their colours vary very
much--black, grey, and iron-colour are everlastingly shaded and
blended together. To that may be added reflections which are above the
ground colour, and which change the hues of the little animal
according to the incidence of the rays of light. The _Anthomyides_
resemble the genus _Musca_ very closely in their habits as well as in
their organisation.
In this group of Diptera we will first say a few words about the
_Anthomiæ_. These flies are to be found in most gardens, and on all
flowers, particularly on the heads of Compositæ and Umbelliferæ. They
often unite in numerous bands in the air, and indulge in the joyous
dances to which love invites them. The females deposit their eggs in
the ground, and their larvæ are there quickly developed. The latter
suspend themselves to certain bodies, the same as some lepidopterous
chrysalides, in order to transform themselves into pupæ.
The _Anthomyia pluvialis_ (Fig. 63) is from two to four lines in
length, and of a whitish ash-colour. Its wings are hyaline, the thorax
has five black spots, and the abdomen three rows of similar spots.
[Illustration: Fig. 63.--Anthomyia pluvialis.]
We will stop a moment with the _Pegomyiæ_, which are very interesting
in the larva state, and which excited the interest and sagacity of
Réaumur.
The cradle of these Diptera is the interior of leaves. They work as
the miners of the vegetable world, in the parenchyma or cellular
tissue of the leaf, between the two epidermal membranes. The henbane,
the sorrel, and the thistle, especially nourish them. If one holds a
leaf in which one of these miners has established itself against the
light, one sees the workman boring the vegetable membrane. Its head is
armed with a hook, formed of two horny pieces, and with this hook it
digs into the parenchyma of the leaf. The effect of this digging is
visible, as those places become by degrees transparent. Each blow
detaches a small portion of the substance of the leaf. It is thus that
these miners hollow out galleries for themselves, in which they find
shelter, food, and security. Some are changed into pupæ in the gallery
which they have hollowed out, others go out of the leaves when they
are near their final transformation.
_Section of Acalyptera._--The _Acalyptera_, which are the last of the
great tribe of _Muscidæ_, comprehend the greater number of these
insects. Their constitution appears to be peculiar and slow. They live
principally in the thickest part of woods, on grasses, and aquatic
plants. Fearing the lustre and warmth of the sun, they never draw the
nectar from flowers. Their flight is feeble, and they never indulge in
those joyous ethereal dances which we have mentioned when speaking of
the preceding groups. Their life is generally melancholy, obscure, and
hidden. Some of them seek decomposed animal and vegetable substances,
others living vegetables.
We shall only be able in this immense group of _Muscidæ_ to mention a
few types which are interesting from various reasons, such as the
_Helomyzæ_, the _Scatophagæ_, the _Ortalides_, the _Daci_, and the
_Thyreophoræ_.
[Illustration: Fig. 64.--A species of Helomyza.]
The _Helomyzæ_ (Fig. 64) live in the woods. Their larvæ are developed
in the interior of fungi. Réaumur studied the larvæ of the Truffle
Helomyza. The head of this fly is ferruginous, its thorax is of a
brownish grey, its shoulders of a brownish yellow, its wings brownish,
the abdomen yellow and brown, and the feet red. The larvæ of these
insects commit depredations for which gourmands will never forgive
them, destroying, as they do, their truffles. When one presses between
one's fingers a truffle that is in a too advanced state, one feels
certain soft parts, which yield under pressure. On opening the
truffle, the larvæ of the insect of which we are speaking will be
found inside. These larvæ are white and very transparent. Their mouth
is armed with two black hooks, by means of which they dig into the
truffle in the same way as other larvæ dig into meat. The excretions
of these little parasites cause the truffle to become decomposed and
rotten. In a few days the larvæ become full-grown. They then leave
their abode and go into the ground, there to change into pupæ.
The _Ortalidæ_ form a tribe which is remarkable for the upright
carriage of the wings, which are generally speckled, by the vibratory
movement of these organs, and especially for the cradle chosen by them
for their progeny in fruits and grains. Nature seems to have assigned
to each species its own particular vegetable.
We will only mention here the Cherry-tree _Ortalis_, whose larva lives
on the pulp of that fruit. This fly is about a line and a half long.
It is of rather a metallic black colour, its head light yellow, the
edges of its eyes white, and the tarsi red. The wings have four broad
black stripes.
[Illustration: Fig. 65.--Dacus oleæ.]
The Olive Dacus (_Dacus oleæ_, Fig. 65) is a little fly, about half
the size of the house fly, of ashy grey colour on the back, its head
orange-yellow, its eyes green, and its forehead yellow, marked with
two large black spots. The thorax is adorned with four lightish yellow
spots, and its hind part, as well as its antennæ and wings, are of the
same colour. The wings are transparent, reflecting green, gold, pink,
and blue, according as the rays of light fall upon them, and are
remarkable for having a small black spot at their extremity. The
abdomen is of a fawn colour or orange-yellow, spotted with black on
each side. This fly performs sudden and jerking movements; it keeps
its wings extended, and rather jumps than flies. It is a destructive
insect, a perfect scourge, which causes every two or three years a
loss of five or six millions of francs to French agriculture.
M. Guérin-Méneville has made some valuable observations on the Olive
Dacus, and at the request of the Imperial Society of Agriculture of
Paris, has indicated the way to preserve the olive from these ruinous
larvæ, which generally destroy two crops out of three. We will borrow
the following details from this learned entomologist: "At the time
when the olives are formed the Dacus proceeds to place an egg under
the skin of each of the fruits. By means of a little horny instrument,
with which the female is provided, and which contains a small lancet,
she pierces the skin of the olive; she moves her wings and lays her
egg. She afterwards cleans and rests herself, by passing her feet over
her head, wings, and other parts of her body. She then flies away, and
seeks another olive, to deposit in it another egg; she repeats this
operation until she has placed on as many olives the three or four
hundred eggs which she bears."
[Illustration: Fig. 66.--Olives attacked by Dacus oleæ.]
Fig. 66, taken from the Memoir published by M. Guérin-Méneville, in
the "Revue Nouvelle" of the 15th July, 1847, shows the Dacus laying
its eggs on the olive, and the larvæ that are already hatched in
another of the same fruit. The larvæ which succeed these eggs (Fig.
67) are whitish, soft, and without limbs. They pass fifteen or sixteen
days in boring a gallery in the pulp of the olive, at first
vertically, until they reach the stone, then on one side, and along
the side of the stone. When they have reached the term of their
development, they approach the surface, enlarging the first channel
and leaving between it and the exterior air only a thin pellicle, in
the middle of which may be perceived the first small opening by which
the mother had introduced her egg in the commencement.
[Illustration: Fig. 67.--Larvæ of Dacus oleæ (magnified and natural
size).]
[Illustration: Fig. 68.--Gallery formed by larva of Dacus oleæ.]
Fig. 68, copied from a drawing in the Memoirs of M. Guérin-Méneville,
shows the gallery bored round the olive by the larva of the Dacus. The
larva thus prepares an easy issue for the perfect insect. Its skin
then contracts, its body diminishes in length, and is transformed into
an oval cocoon, which soon gets brown, and is the chrysalis of the
insect. At the side of the head it shows a curved line, a thin suture
which marks a sort of cap or door, which, at the time of its hatching,
the insect will be easily able to force open with its head. The fly is
hatched twelve days after its metamorphosis from the larva to the
pupa. It has thus taken the Dacus twenty-seven to twenty-eight days to
arrive at this state, from the time the egg was laid; besides which,
this species, in the warm climates of Provence and Italy, can
reproduce itself several times from the beginning of July, the period
at which the first flies begin to lay, till the end of autumn.
In order to save a considerable portion of the olive crop of these
countries, M. Guérin-Méneville has advised hastening the harvest
sufficiently for all the olives to be pressed at a time when the larvæ
of the last generation, which would be preserved in the olives that
are left, or in the earth, according to the climate, are still in the
fruit. If a first operation were not sufficient to destroy them all,
it should be repeated the following year. The sacrifice entailed by
this practice would be amply compensated by a succession of good crops
and the certainty of a sure and permanent profit. In fact, by an early
gathering at least half a crop of oil is still obtained; whereas, by
waiting for the usual period of gathering the olives, sufficient time
is left for the larvæ of the Dacus to devour their parenchyma, which
deprives them of the little oil that they might have yielded if their
destruction had been accomplished earlier. This early gathering has
the advantage of causing the destruction of a great number of larvæ,
which will be so much towards diminishing the means of reproduction of
the fly.