_Pepsis_, a genus peculiar to America, whence upwards of 200 species are
already known.[48] Some of them attain a length of two inches or more, and
are able to conquer the largest spiders; even the formidable _Mygale
avicularis_ succumbs to their agility and skill. Some of these _Pepsis_
have beautifully coloured wings; according to Cameron, this may be {105}due
to scales. _P. formosus_, Say, is called in Texas the tarantula-killer;
according to Buckley, its mode of attack on the huge spider is different
from that made use of by its European ally. When it discovers a tarantula
it flies "in circles in the air, around its victim. The spider, as if
knowing its fate, stands up and makes a show of fighting, but the
resistance is very feeble and of no avail. The spider's foe soon discovers
a favourable moment and darts upon the tarantula, whom it wounds with its
sting, and again commences flying in circles." The natural retreat of this
huge spider, _Mygale hentzii_, is in holes in the ground, and this account
does not inform us whether the spider allows itself to be overcome when in
its nest, or is only attacked when out of its retreat.
The genus _Mygnimia_ includes a very large number of species, and has a
wider geographical distribution than _Pepsis_, being found in the tropical
regions of both the Old and New Worlds, some of them rivalling in size and
ferocity the larger specimens of the genus _Pepsis_. In the Insects of this
genus there is usually a more or less distinct small space of more pallid
colour on the middle of each front wing. _Parapompilus_ is a curious genus
consisting of Insects of a great variety of peculiar coloration, and having
the wings short, so as to be of little use for flight. _P. gravesii_ is an
inhabitant of Chili.
_Agenia carbonaria_ and _A. hyalipennis_ are small and feeble Insects
inhabiting the south of Europe. _A. carbonaria_ extends to the south of
England. They construct, as nests for their offspring, small earthenware
vessels, differing in form according to the species, those of _A.
hyalipennis_ being vase-like in shape, while those of _A. carbonaria_ are
contracted near the mouth, something after the fashion of a wide-mouthed
bottle. The Insect is able by some means—Fabre thinks by the use of
saliva—to varnish the interior of the vessel so that it will not absorb
water; the outside of the cells is, however, not so protected, and speedily
crumbles away when exposed to the action of water; hence the vessel is
placed in a protected situation, such as in a tree-stump, or a hole in a
wall, or even in an empty snail-shell under a heap of stones. The cells are
stored with spiders that have been paralysed by stinging and that serve as
food for the larva of the _Agenia_. The larva of _A. carbonaria_ has been
described, and some particulars as to its habits have been given by
Verhoeff. {106}It has been stated that this wasp does not paralyse its prey
by stinging, but substitutes a process of biting to prevent the spider from
hurting the larva that is to feed on it; and Verhoeff's observations seem
to show that the legs of the spider are broken by some proceeding of the
kind. The _Agenia_ larva is of peculiar shape, the head not being inflexed,
while the pleurae of each segment, from the second onwards, are prominent,
so as to give the outline of the body a scalloped appearance. This larva is
much infested by an Ichneumon that devours, it appears, not only the larva
itself, but also the spider that was destined to be food for the larva.
Verhoeff seems to have found some evidence that _Pompilus sericeus_ may
also be a parasite on the _Agenia_.
The construction of earthenware cells, instead of the burrows usual in
Pompilidae, by the species of this genus is one of the cases alluded to in
our introductory remarks as to allied Fossores exhibiting different habits.
Mr. Pride has recently sent us from Brazil similar earthen vessels
constructed by some Pompilid.
The habits of Pompilids of the genus _Ceropales_ are analogous to those of
the parasitic bees. Pérez has recently given us information as to a very
curious form of parasitism in this genus; he says that when a _Pompilus_
has obtained a spider as provision for its young, it is pursued by a
_Ceropales_, which lays an egg on the spider, thus as it were substituting
in advance its own young for that of the _Pompilus_. Information as to the
subsequent course of events in this case is not at present forthcoming. In
another case a _Ceropales_ was observed to oviposit on the spider, not
while this is being carried in, but subsequently by entering the nest for
the purpose; a habit quite similar to that of some parasitic bees. Ferton
has recently made the unexpected discovery that some _Pompilus_ act as
robbers; one individual taking away by force the spider that another has
captured and is carrying off.
Lichtenstein described a Pompilid larva, that he afterwards ascertained to
be _Calicurgus hyalinatus_, as possessing the extraordinary habit of
feeding as an external parasite fixed to the dorsal surface of a spider;
thus repeating, it would appear, the habits of some of the Ichnemonidae,
though the perfect Insect (Fig. 143) does not differ in structure from its
congeners. Emery has given an account of some Pompilids that do not bury
their prey, but after stinging it and depositing an egg, simply leave the
spider on the spot.
{107}Buller has described the habits of a Pompilid in New Zealand; his
account is interesting because it shows a remarkable similarity in the
proceedings of this antipodean wasp to those of its congeners on our own
side of the world. The species is not scientifically named, but it appears
that it is known in New Zealand as "the Mason-bee." It forms a nest of
yellow clay consisting apparently of about eight cells, each of which is
filled with one or more spiders in a paralysed condition. The figure given
of the larva of this Insect by Buller shows it to possess a peculiarly
formed head.
It is pleasing to find that Pompilidae do not make use of cruel methods
when others will serve their purpose. We are informed that a large
Australian Pompilid—_Priocnemis bicolor_—may find a _Cicada_ sucking sap
from a hole it has pierced in a tree. The _Priocnemis_ has not the art of
making the puncture necessary to procure sap, so the wasp seizes the
_Cicada_, and shakes it till it leaves its hold and flies away, when the
_Priocnemis_ takes its place and sips the sap. It is added that the wasp
never hurts the Cicada.
FAM. 3. SPHEGIDAE.
_Pronotum free from the tegulae; when the stigmatic lobes extend as far
back as the wing-insertion, they are placed below it and separated by a
space from it._
This large assemblage of Fossores is the one about which the greatest
difference of opinion prevails. It is based entirely on the prothoracic
characters mentioned above, and cannot be looked on as natural. We shall,
however, follow Kohl[49] in treating for the present as only one family the
divisions considered by many as distinct families. They are ten in number.
SUB-FAM. 1. SPHEGIDES.—_Hind body with a slender pedicel of variable
length; two spurs on the middle tibia. The propodeum usually horizontally
elongate_.[50]
This group includes a great number of species, about 200 of which are
referred to the genus _Sphex_.
{108}The habits of one species of this genus have been fully described by
Fabre; he assigns to the species the name of _S. flavipennis_, but Kohl
considers that it is more probably _S. maxillosus_. This Insect forms its
nests, in the South of France, in the ground, excavating a main shaft with
which are connected cells intended for the reception of the provisions for
the young. The entrance to the burrow is formed by piercing a hole in the
side of a very slight elevation of the soil. Thus the entrance to the
construction consists of a horizontal gallery, playing the part of a
vestibule, and this is used by the _Sphex_ as a place of retreat and
shelter for itself; at the end of the vestibule, which may be two or three
inches long, the excavation takes an abrupt turn downwards, extending in
this manner another two or three inches, and terminating in an oval cell
the larger diameter of which is situate in a horizontal plane. When this
first cell has been completed, stored with food, and an egg laid in it, the
entrance to it is blocked up, and another similar cell is formed on one
side; a third and sometimes a fourth are afterwards made and provisioned,
then the Insect commences anew, and a fresh tunnel is formed; ten such
constructions being the number usually prepared by each wasp. The Insect
works with extreme energy, and as the period of its constructive activity
endures only about a month, it can give but two or three days to the
construction and provisioning of each of its ten subterranean works. The
provisions, according to Fabre, consist of a large species of
field-cricket, of which three or four individuals are placed in each cell.
Kohl states, however, that in Eastern Europe an Insect that he considers to
be the same species as Fabre's _Sphex_, makes use of locusts as provisions,
and he thinks that the habit may vary according to the locality or to the
species of Orthoptera that may be available in the neighbourhood. However
that may be, it is clear from Fabre's account that this part of the
_Sphex's_ duties do not give rise to much difficulty. The cricket, having
been caught, is paralysed so that it may not by its movements destroy the
young larva for whose benefit it is destined. The _Sphex_ then carries it
to the burrow to store it in one of the cells; before entering the cell the
Insect is in the habit of depositing its prey on the ground, then of
turning round, entering the burrow backwards, seizing as it does so the
cricket by the antennae, and so dragging it into the cell, itself going
{109}backwards. The habit of depositing its prey on the ground enabled
Fabre to observe the process of stinging; this he did by himself capturing
a cricket, and when the wasp had momentarily quitted its prey, substituting
the sound cricket for the paralysed one. The _Sphex_, on finding this new
and lively victim, proceeds at once to sting it, and pounces on the
cricket, which, after a brief struggle, is overcome by the wasp; this holds
it supine, and then administers three stings, one in the neck, one in the
joint between the pro- and meso-thorax, and a third at the base of the
abdomen, these three spots corresponding with the situation of the three
chief nervous centres governing the movements of the body. The cricket is
thus completely paralysed, without, however, being killed. Fabre proved
that an Insect so treated would survive for several weeks, though deprived
of all power of movement. Three or four crickets are placed by the wasp in
each cell, 100 individuals or upwards being thus destroyed by a single
wasp. Although the sting has such an immediate and powerful effect on the
cricket, it occasions but a slight and evanescent pain to a human being;
the sting is not barbed, as it is in many bees and true wasps, and appears
to be rarely used by the Insect for any other purpose than that of
paralysing its victims. The egg is laid by the _Sphex_ on the ventral
surface of the victim between the second and third pairs of legs. In three
or four days the young larva makes its appearance in the form of a feeble
little worm, as transparent as crystal; this larva does not change its
place, but there, where it was hatched, pierces the skin of the cricket
with its tiny head, and thus begins the process of feeding; it does not
leave the spot where it first commenced to feed, but gradually enters by
the orifice it has made, into the interior of the cricket. This is
completely emptied in the course of six or seven days, nothing but its
integument remaining; the wasp-larva has by this time attained a length of
about 12 millimetres, and makes its exit through the orifice it entered by,
changing its skin as it does so. Another cricket is then attacked and
rapidly consumed, the whole stock being devoured in ten or twelve days from
the commencement of the feeding operations; the consumption of the
later-eaten crickets is not performed in so delicate a manner as is the
eating of the first victim. When full-grown, the process of forming a
cocoon commences: this is a very elaborate operation, for the encasement
consists of three layers, in {110}addition to the rough silk that serves as
a sort of scaffolding on the exterior: the internal coat is polished and is
of a dark colour, owing to its being coloured with a matter from the
alimentary canal: the other layers of the cocoon are white or pale yellow.
Fabre considers that the outer layers of the cocoon are formed by matter
from the silk-glands, while the interior dark coat is furnished by the
alimentary canal and applied by the mouth of the larva: the object of this
varnish is believed to be the exclusion of moisture from the interior of
the cocoon, the subterranean tunnels being insufficient for keeping their
contents dry throughout the long months of winter. During the whole of the
process of devouring the four crickets, nothing is ejected from the
alimentary canal of the larva, but after the cocoon is formed the larva
ejects in it, once for all, the surplus contents of the intestine. Nine
months are passed by the Insect in the cocoon, the pupal state being
assumed only towards the close of this period. The pupa is at first quite
colourless, but gradually assumes the black and red colour characteristic
of the perfect wasp. Fabre exposed some specimens of the pupa to the light
in glass tubes, and found that they went through the pupal metamorphosis in
just the same manner as the pupae that remained in the darkness natural to
them during this stage of their existence.
_Sphex coeruleus_ is frequently stated to have the habit of provisioning
its nests with both Orthoptera and Spiders; but Kohl considers with reason
that this record is, as regards spiders, a mistake, arising probably from a
confusion with some other Insect of similar appearance, such as _Pelopaeus_
(_Sceliphron_) _coeruleus_. _S. coeruleus_ is no doubt the same as _S._
(_Chlorion_) _lobatus_, which Rothney observed in East India, provisioning
its nests with Orthoptera. He discovered a nest in process of construction,
and during the absence of the mother-wasp abstracted from the burrow a
large field-cricket that she had placed in it; he then deposited the
Orthopteron near the cell; the parent _Sphex_ on returning to work entered
the tunnel and found the provision placed therein had disappeared; she came
out in a state of excitement, looked for the missing cricket, soon
discovered it, submitted it to the process of malaxation or kneading, and
again placed it in the nest, after having cleared it from some ants that
had commenced to infest it. She then disappeared, and Rothney repeated the
experiment; in due course the same series {111}of operations was performed,
and were repeated many times, the _Sphex_ evidently acting in each case as
if either the cricket had disappeared owing to its being incompletely
stunned, or to its having been stolen by ants. Finally, the observer placed
the cricket at a greater distance from the nest, when it recovered from the
ill-treatment it had received sufficiently to make its escape. The points
of interest in this account are the fact that the cricket was only
temporarily paralysed, and that the wasp was quite able to cope with the
two special difficulties that must frequently occur to the species in its
usual round of occupations.
The genus _Ammophila_ is of wide distribution, and its species make
vertical tunnels in the ground. The habits of some of the species found in
France have been described by Fabre. The Insect does not inhabit the burrow
while it is in process of formation, but quits it; and some of the species
temporarily close the entry to the incomplete nest with a stone. The tunnel
is a simple shaft with a single cell at its termination; this is stored
with caterpillars, the different species of _Ammophila_ selecting different
grubs for the purpose. _A. hirsuta_ hibernates in the perfect state, and
carries on its work in the spring; it chooses a single larva of
considerable size belonging to one of the nocturnal Lepidoptera, and this
it paralyses by a series of about nine stings, of which one is implanted in
each segment from the first thoracic ring backwards; it forms the burrow
only after the food to be placed therein has been obtained. The caterpillar
used is subterranean in habit, and the _Ammophila_ detects the larva by
some sense, the nature of which appears at present quite uncertain. _A.
holosericea_ chooses smaller larvae of the family Geometridae, and uses
only one or two stingings to paralyse each larva; several caterpillars are
used to provision a single cell, and they are often selected of different
colours.
Marchal has also published an important account of the proceedings of _A.
affinis_; he confirms Fabre's observations, and even adds to their interest
by suggesting that the _Ammophila_ administers special stings for the
purpose of paralysing the mandibles of the caterpillar and depriving it of
any power of afterwards injuring the larva that will feed on it. He thinks
the mother-_Ammophila_ herself profits by appropriating an exudation from
the victim.
Some species of Sphegides have the curious habit of choosing {112}the
interiors of human habitations as the spots most suitable for the formation
of their own domestic establishments. Fabre has given a charming account of
the habits of _Pelopaeus_ (_Sceliphron_) _spirifex_, a species that
inhabits the South of Europe, and that forms its nests in the cottages of
the peasants. The spot usually selected is a nook in the broad, open
fireplace, out of reach of the flames, though not of the smoke; here the
_Pelopaeus_ forms a nest of earth, consisting of ten to fifty cells, the
material being mud or clay brought in little balls by the aid of the
Insect's mandibles; about twenty visits are required in order to complete
one cell, so that for the construction of a large nest of fifty cells,
about one thousand visits must be made by the Insect. It flies in and out
of the house apparently not at all incommoded by the human habitants, or by
the fact that the peasant's potage may be simmering on the fire quite close
to where the fearless little creature is carrying on its architectural
operations. The cells are stored with spiders, of which the wasp has to
bring a plentiful supply, so that its operations extend over a considerable
period. The prey is captured by the _Pelopaeus_ whilst on the wing, and
carried off at once, being probably stung by the wasp during the process of
transit; apparently it is killed by the operation, not merely paralysed.
Only small spiders are taken by this species, and the larva of the
_Pelopaeus_ consumes them in a short time, one by one, before the process
of decomposition sets in; the egg, too, is laid on the first spider
introduced, and this is of course at the bottom of the cell, so that the
spiders are eaten by the wasp's larva in the order in which they were
brought to the cell. The cell is sealed up when full, the number of spiders
placed in it being on the average about eight. The larva completes its task
of consuming the store in about ten days, and then forms a cocoon for its
metamorphosis. Two or three generations are produced in a single year, the
autumnal one passing eight or nine months in the clay cells, which are
lodged in a nook of the peasant's hearth, and exposed to the smoke of his
fire during all the months of winter. _Pelopaeus_ (_Sceliphron_) is a genus
including many species;[51] several of them are known {113}to be specially
attached to the habitations of human beings. Roth has given an account of
the habits of _P._ (_Sceliphron_) _laetus_ in Australia; he says that in
some parts it is very difficult to keep these wasps out of the houses; the
nest is formed of mud, and constructed on the furniture or in any part of a
room that suits the fancy of the Insect. This it must be admitted is,
according to human ideas, liable to the charge of being very capricious.
Roth timed a wasp building its nest, and found that it brought a fresh load
of mud every two or three minutes. If the wasp be allowed to complete the
nest undisturbed, she does so by adding to the exterior diagonal streaks of
mud, so giving to the nest the look of a small piece of the bark of a
common acacia. The construction consists of from ten to twenty cells, and
when completed is provisioned with spiders for the use of the young. This
wasp is much pestered by parasites, some of which prevent the development
of the larvae by consuming the spiders intended by the mother-wasp for its
young. A fly, of the Order Diptera, is said to follow the wasp when
carrying a spider, and to deposit also an egg on the food; as the Dipterous
larvae have more rapid powers of assimilation, the _Pelopaeus_ larvae are
starved to death; and their mildewed remains may be found in the cell,
after their enemies have become fully developed and have flown away.
Another parasite is said to eat the wasp-larva, and attains this end by
introducing an egg through the mud wall and the cocoon of the wasp—a habit
that seems to indicate a _Leucospid_ parasite. _Tachytes australis_, a wasp
of the sub-family Larrides also dispossesses this _Pelopaeus_ in a manner
we shall subsequently describe. This fragment of natural history from
Australia has a special interest, for we find repeated there similar
complex biological relations to those existing in the case of the European
congeners.
_P._ (_Sceliphron_) _madraspatanus_ is common in the north-west provinces
of Hindostan, and is called the "mud-dauber" by the European residents.
According to Horne it constructs its cells in the oddest places, but
chiefly about the inhabited apartments in houses. It is perfectly fearless
when engaged in building: the cells are four to six in number, and are
usually provisioned with spiders to the number of about twenty. On one
occasion it was observed that green caterpillars were stored instead of
{114}spiders. The species is said to be protected by a peculiar odour as
well as by its sting; it is also stated that it disguises its edifice when
completed by making it look like a dab of mud, and on one occasion "rays of
mud were observed round the nest, even more exactly imitating a lump of mud
thrown with some force." _P._ (_Sceliphron_) _bilineatus_, formerly thought
to be a variety of _P. madraspatanus_, builds its nests in hedges and
trees.
SUB-FAM. 2. AMPULICIDES.—_Prothorax long and narrow, forming a neck in
front; clypeus beak-like; four submarginal cells, the outer one being
complete; metathorax elongate, the posterior part of the metasternum
deeply divided to allow a perfect inflection of the abdomen._
[Illustration: Fig. 44—_Ampulex compressa_. Male. East India.]
This is one of the smallest of the divisions of the Sphegidae, but has a
very wide distribution, being represented in both the Eastern and Western
Hemispheres. It is allied to the Sphegides, but differs by the prolongation
of the neck and of the head, and by the articulation between the petiole
and thorax being placed on the under surface of the body; the wing-nervures
are said to be of inferior importance owing to their frequently differing
in individuals of the same species. These Insects appear to be rare in
individuals, as well as few in species, and but little has been recorded as
to their habits; but it is known that they live on cockroaches. Perkins has
given a brief sketch of the habits of _Ampulex sibirica_ that is of great
interest, but requires confirmation. He says that this Insect, in West
Africa, enters apartments where cockroaches abound, and attacking one, that
may probably be four times its own size, succeeds, after a struggle, in
stinging it; the cockroach instantly becomes quiet and submissive, and
suffers itself to be led away and placed in confinement in some {115}spot
such as a keyhole, and in one case was apparently prevented from afterwards
escaping, by the wasp carrying some heavy nails into the keyhole. The larva
of the _Ampulex_ may be presumed to live on the Blattid, as it is added
that dead bodies of the cockroaches are frequently found with the empty
cocoon protruding from them. This account, if correct, points to some
features in the habits of this Insect that are unique. A remark made by
Rothney in reference to the habits of _A._ (_Rhinopsis_) _ruficornis_ seems
to indicate some similar instinct on the part of that species; he says, "I
also saw two or three of these wasps collar a peculiar cockroach by the
antennae and lead it off into a crack in the bark, but as the cockroach
reappeared smiling each time, I don't know what was up." The same observer
records that this species associates with _Sima rufonigra_, an ant it
greatly resembles in appearance, as well as with a spider that is also of
similar appearance (Fig. 72). Schurr has given a brief account of the
proceedings of _Ampulex compressa_, and his statements also tend to confirm
the correctness of Perkins' report. The habits of a species of _Ampulex_
were partially known to Réaumur, who described them on the authority of M.
Cossigni. The species is believed to be _A. compressa_, which occurs not
only in East India, but also in the island of Bourbon, the locality where
M. Cossigni made his observation: his account is, like the others, a mere
sketch of certain points observed, the most important of which is that when
_Ampulex_ cannot introduce the cockroach into a hole that it has selected
as suitable, it bites off some portions of the body in order to reduce the
poor Insect to the necessary extent.
From these fragmentary observations it would appear that the sting of the
_Ampulex_ has not so powerful a paralysing effect as that of most other
Fossores; and that the _Ampulex_ does not form any nest, but takes
advantage of suitable holes and crevices to store the victim in; also that
it displays considerable ingenuity in the selection of materials with which
to block up the cavity in which it has placed the partially incapacitated
creature.
The genus _Dolichurus_ is by some entomologists considered the type of a
sub-family allied to the Ampulicides; it long consisted of a small and rare
European Insect, but some exotic species have recently been added to it. It
will probably prove not {116}sufficiently distinct from Ampulicides,
although the pronotum is much shorter, but Handlirsch has recently observed
that the European species attacks Blattidae as do the normal Ampulicides;
and Ferton has recorded that _D. haemorrhous_ lives at the expense of
_Loboptera decipiens_, the wasp depositing its egg on the left intermediate
femur of the prey. This is placed in a solitary cell, and is entirely
consumed by the larva, life being preserved till within a few hours of the
end of the repast, which occupies altogether eight days.
SUB-FAM. 3. LARRIDES.—_Hind body not pedicellate, or with only a short
pedicel; one spur on the middle tibia; labrum inconspicuous. Marginal
cell of the front wings appendiculate,[52] or mandibles excised
externally, or both._
This group is by some writers called Tachytides instead of Larrides, as
owing to a change of nomenclature _Tachytes_ may now be considered its
principal genus. It is in connection with this and the neighbouring
sub-families of Sphegidae that some of the greatest taxonomical
difficulties exist. We include in Larrides the "_Miscophus_ group" of Kohl.
The species of the genus _Tachytes_ seem to have habits very similar to
those of the genus _Sphex_; they form shafts in the earth and provision
them with Orthoptera; like the _Sphex_ and other Fossores, they have the
habit, when they fly to their tunnel with a victim, of depositing it for a
short time on the ground close to the mouth of the burrow while they turn
round and enter backwards; and, after doing this they again seize their
prey and drag it into the burrow. Fabre availed himself of an opportunity
to remove the prey while the Hymenopteron was entering the hole alone; as a
result it had to come out again to seek the object; this it soon found, and
carried to the hole, relinquishing it again as usual while it turned round;
Fabre repeated the operation several times, and always with the same
result; the wasp, though it might have kept hold of the victim while it
turned, and thus have saved itself from losing the precious object, never
did so.
{117}One species of _Tachytes_ in the south of France selects as its prey
Orthoptera of the family Mantidae, Insects of a highly ferocious
disposition, and provided with most powerful front legs, capable of cutting
in two by a single act the body of an aggressor like the _Tachytes_; the
latter is, however, by no means dismayed by the arms of its future victim,
but hovering above the latter for some time, as if to confuse it, and
causing it repeatedly to turn its very mobile head, the _Tachytes_ at last
pounces down and instantaneously stings the _Mantis_ in the nerve centre
between the formidable arms, which at once are reduced to incapacity;
subsequently the _Tachytes_ paralyses each of the other pairs of legs, and
then carries off its victim.
[Illustration: Fig. 45.—_Tachytes pectinipes_ ♀. Britain.]
_Larra anathema_ chooses mole-crickets as the viand for its young, and
_Tachysphex panzeri_ selects grasshoppers of the family Acridiidae. _Larra
pompiliformis_ (= _Tachytes niger_, Fabre) sometimes associates itself with
_Sphex flavipennis_ (_? S. maxillosus_, according to Kohl), forming its
burrow amidst the works of a colony of that species, and making use, like
the _Sphex_, of crickets for provender. This led Fabre to believe that the
_Larra_ stole its prey from the _Sphex_, but he has since withdrawn this
indictment, and declares that the _Larra_ obtains its crickets by the more
honourable, if not more humane, process of catching and stinging them
itself. Smith has informed us, on the faith of his own observation, that
_L. pompiliformis_ uses both Lepidopterous larvae and grasshoppers for its
stores.
_T._ (_Larrada_) _australis_, according to Whittell, plays the part of a
burglar, breaking open the cells of _Pelopaeus_ (_Sceliphron_) _laetus_
after they have been completed and stored with spiders; it then takes
possession of the cell, and curiously enough the _Pelopaeus_ permits this,
although the cell contains its egg and the store of food that is intended
for the use of its own young. To us this seems very strange, but it is
probable that the _Pelopaeus_ has no idea of the consequences of the
intruder's operations; {118}it being one of the strange facts of nature
that these highly endowed creatures never even see the offspring for whose
welfare they labour with such extraordinary ingenuity and perseverance.
Neither can we suppose that they have a conception of it derived from a
knowledge of their own individual history; for their very complete
metamorphosis is scarcely reconcilable with any such recollection on their
part. It may possibly therefore be the case that, having no idea whatever
of the offspring, they are equally destitute of any conception that it will
be destroyed by the operations of the _Larrada_. However this may be,
Whittell informs us that both wasps skirmish about for a little as if each
were mistrustful and somewhat afraid of the other; this ends by the
_Pelopaeus_ withdrawing its opposition and by the _Larrada_ taking
possession of the cell, which it then proceeds to divide into two, using
for the purpose of the partition portions of the material of the nest
itself; possibly it is only a contraction of the size of the cell, not a
true division, that is effected; however this may be, after it is
accomplished the _Larrada_ deposits its own egg in the cell, having, it is
believed by Whittell, previously destroyed that of the _Pelopaeus_. Judging
from what occurs in other species it is, however, more probable that the
destruction of the egg or young of the _Pelopaeus_ is carried out by the
larva of the _Larrada_ and not by the parent-wasp. From a remark made by
Maindron as to the proceedings of _Larrada modesta_, in Ternate, it seems
probable that its habits may prove to be similar to those of _L.
australis_, for it frequents the nests of _Pelopaeus_ after they have been
completed.
SUB-FAM. 4. TRYPOXYLONIDES.—_Differ from Larrides by the inner margin of
the eyes being concave, and the marginal cell not appendiculate. (In_
Trypoxylon _there is only one distinct submarginal and one distinct
discoidal cell, a second of each being indicated faintly.)_
The nervuration of _Trypoxylon_ is very peculiar, and differs from that of
the widely-distributed genus _Pison_, though according to Kohl's views the
two may be correctly associated to form this sub-family. The species of
_Trypoxylon_ are apparently rather fond of human propinquity, and build
clay- or mud-nests in or near houses. _T. albitarse_ has this habit, and is
well known in Southern Brazil under the name of "_Marimbouda da casa_";
{119}this Insect, like _Pelopaeus_, stores its nest with spiders, and
Peckholt has remarked that however great may be the number of spiders
placed by the mother-wasp in a cell, they are all consumed by the larva,
none ever being found in the cell after the perfect Insect escapes
therefrom. The European _T. figulus_ forms a nest either in bramble-stems
or in sandy soil or walls; it makes use of spiders as provisions.
SUB-FAM. 5. ASTATIDES.—_Eyes very large in the male, meeting broadly on
the vertex; two spurs on the middle tibia._
[Illustration: Fig. 46—_Astata boops_, male. Britain.]
We have two species of the genus _Astata_ in Britain: one of them—_A.
boops_—is known to form burrows in the ground, each of which contains only
a single cell; this, it appears, is usually provisioned with bugs of the
genus _Pentatoma_, Insects remarkable for their strong and offensive odour.
St. Fargeau records that this species also makes use of a small cockroach
for forming the food-store: thus exhibiting an unique catholicity in the
toleration of the disagreeable; almost the only point of connection between
bugs and cockroaches being their disagreeable character. According to
Smith, _Oxybelus_, another genus of Fossores, is also used. Authorities are
far from agreement as to the validity and relations of the sub-family
Astatides. It consists only of the widely-distributed genus _Astata_, with
which the North American _Diploplectron_ (with one species) is doubtfully
associated.
SUB-FAM. 6. BEMBECIDES.—_Labrum frequently elongate; wing-nervures
extending very near to the outer margin; marginal cell of front wing not
appendiculate; mandibles not emarginate externally; hind body stout, not
pedicellate._
The elongation of the labrum, though one of the most trustworthy of the
characters of the Bembecides, cannot be altogether {120}relied on owing to
the variation it presents both in this and the allied sub-families. The
Bembecides carry their prey to their young tucked underneath their own
bodies and hugged to the breast; they affect loose, sandy soils for
nidification; make use, in the great majority of the cases where the habits
are known, of Diptera for provisions, and give these dead to the young;
making repeated visits to supply fresh food to the progeny, which
notwithstanding this fact, are distributed in isolated burrows.
[Illustration: Fig. 47.—_Bembex rostrata_ ♂. Europe.]
One of the most interesting of Fabre's studies of the instincts of
Hymenoptera is devoted to _Bembex rostrata_. The Bembecides have the habit
of forming their nests in the ground in wide expanses of sand, and of
covering them up, they leave them so that there appears to be absolutely
nothing by which the exact position of the nest can be traced; nevertheless
the _Bembex_ flies direct to it without any hesitation. How necessary it is
to these Insects to possess this faculty of finding their nests will be
understood when we recall that the _Bembex_ does not provision its nest
once and for all, but supplies the young at first with only insufficient
food, and has therefore to return at daily, or other intervals, with a
fresh store of provisions. The burrow is made in the sand by means of the
fore-legs; these work with such rapidity and skill that a constant stream
of sand flows out behind the Insect while it is engaged in the act of
excavation. The nest or cell in which the larva is to live, is formed by
this process of digging; but no fastening together of the material occurs,
nor does any expedient seem to be resorted to, other than that of making a
way through the sand by clearing out all the pieces of stick or stone that
might diminish facility of access. The cell being formed, the _Bembex_
leaves the spot in search of prey, and when it has secured a victim in the
shape of a two-winged fly, it returns therewith to the burrow, and the
booty is placed therein, an egg being deposited on it. The wasp then leaves
the burrow, disguising, however, the spot where it is situate, and flies
away; to proceed possibly with the formation {121}of other burrows.[53] In
the course of twenty-four hours the egg hatches, and the larva in two or
three days completely devours the stock provided for it. The mother-wasp
then returns with another fly—this time probably a larger one—penetrates
rapidly to the bottom of the burrow, and again retreats, leaving the second
stock of provisions for the benefit of the greedy larva. These visits of
supply are repeated with increased frequency, as the appetite of the larva
for the benefit of which they are made increases with its growth. During
the fourteen or fifteen days that form this portion of the life-cycle, the
single larva is supplied with no less than fifty to eighty flies for food.
To furnish this quantum, numerous visits are made to each burrow, and as
the mother _Bembex_ has several burrows—though how many does not appear to
be known—her industry at this time must be very great. All the while, too,
a great danger has to be avoided, for there is an enemy that sees in the
booty brought by the _Bembex_ to its young, a rich store for its own
progeny. This enemy is a feeble, two-winged fly of the family Tachinidae
and the genus _Miltogramma_; it hangs about the neighbourhood of the nests,
and sooner or later finds its opportunity of descending on the prey the
_Bembex_ is carrying, choosing for its purpose a moment when the _Bembex_
makes a brief delay just at the mouth of the burrow; then down comes the
_Miltogramma_ and lays one, two, or three eggs on some portion of the booty
that may be projecting from beneath the body of the wasp. This latter
carries in the food for its own young, but thus introduces to the latter
the source of its destruction, for the _Miltogramma_ larvae eat up the
supply of food intended for the _Bembex_ larvae, and if there be not enough
of this provender they satisfy their voracity by eating the _Bembex_ larva
itself. It is a remarkable fact that notwithstanding the presence of these
strange larvae in the nest the mother _Bembex_ continues to bring food at
proper intervals, and, what is stranger still, makes no effort to rid the
nest of the intruders: returning to the burrow with a supply of food she
finds therein not only her legitimate offspring, a single tenant, but
several others, strangers, it may be to the number of twelve; although she
would have no difficulty in freeing the nest from this band of little
brigands, she makes no attempt to do so, but continues to bring the
{122}supplies. In doing so she is fulfilling her duty; what matters it that
she is nourishing the enemies of her race? Both race and enemies have
existed for long, perhaps for untold periods of time, why then should she
disturb herself, or deviate from her accustomed range of duties? Some of us
will see in such proceedings only gross stupidity, while others may look on
them as sublime toleration.
The peculiar habits of _Bembex rostrata_ are evidently closely connected
with the fact that it actually kills, instead of merely paralysing, its
prey; hence the frequent visits of supply are necessary that the larvae may
have fresh, not putrefying, food; it may also be because of this that the
burrow is made in a place of loose sand, so that rapid ingress may be
possible to the _Bembex_ itself, while the contents of the burrow are at
the same time protected from the inroads of other creatures by the burrow
being filled up with the light sand. Fabre informs us that the _Bembex_
larva constructs a very remarkable cocoon in connection with the peculiar
nature of the soil. The unprotected creature has to pass a long period in
its cocoon, and the sandy, shifting soil renders it necessary that the
protecting case shall be solid and capable of keeping its contents dry and
sound. The larva, however, appears to have but a scanty supply of silk
available for the purpose of constructing the cocoon, and therefore adopts
the device of selecting grains of sand, and using the silk as a sort of
cement to connect them together. For a full account of the ingenious way in
which this difficult task is accomplished the reader should refer to the
pages of Fabre himself. Bembecides appear to be specially fond of members
of the Tabanidae (or Gad-fly family) as provender for their young. These
flies infest mammals for the purpose of feasting on the blood they can draw
by their bites, and the Bembecides do not hesitate to capture them while
engaged in gratifying their blood-thirsty propensities. In North America a
large species of Bembecid sometimes accompanies horsemen, and catches the
flies that come to attack the horses; and Bates relates that on the Amazons
a Bembecid as large as a hornet swooped down and captured one of the large
blood-sucking Motuca flies that had settled on his neck. This naturalist
has given an account of some of the Bembecides of the Amazons Valley,
showing that the habits there are similar to those of their European
congeners.
{123}_Sphecius speciosus_ is a member of the Stizinae, a group recognised
by some as a distinct sub-family. It makes use, in North America, of
Insects of the genus _Cicada_ as food for its young. Burrows in the ground
are made by the parent Insect; the egg is deposited on the _Cicada_, and
the duration of the feeding-time of the larva is believed to be not more
than a week; the pupa is contained in a silken cocoon, with which much
earth is incorporated. Riley states that dry earth is essential to the
well-being of this Insect, as the _Cicada_ become mouldy if the earth is at
all damp. As the _Cicada_ is about twice as heavy as the _Sphecius_ itself,
this latter, when about to take the captured burden to the nest, adopts the
plan of climbing with it to the top of a tree, or some similar point of
vantage, so that during its flight it has to descend with its heavy burden
instead of having to rise with it, as would be necessary if the start were
made from the ground.
SUB-FAM. 7. NYSSONIDES.—_Labrum short; mandibles entire on the outer
edge; hind body usually not pedicellate; wing with the marginal cell not
appendiculate._
This group has been but little studied, and there is not much knowledge as
to the habits of the species. It is admitted to be impossible to define it
accurately. It is by some entomologists considered to include _Mellinus_,
in which the abdomen is pedicellate (Fig. 48), while others treat that
genus as forming a distinct sub-family, Mellinides. Kohl leaves _Mellinus_
unclassified. Gerstaecker has called attention to the fact that many of the
Insects in this group have the trochanters of the hind and middle legs
divided: the division is, as a rule, not so complete as it usually is in
Hymenoptera Parasitica; but it is even more marked in some of these
Nyssonides than it is in certain of the parasitic groups.
_Mellinus arvensis_ is one of our commonest British Fossores, and we are
indebted to the late F. Smith for the following account of its habits: "It
preys upon flies, and may be commonly observed resorting to the droppings
of cows in search of its prey; it is one of the most wary and talented of
all its fraternity; were it at once to attempt, by a sudden leap, to dart
upon its victim, ten to one it would fail to secure it; no, it does no such
thing, it wanders about in a sort of innocent, unconcerned way, amongst
{124}the deluded flies, until a safe opportunity presents itself, when its
prey is taken without any chance of failure; such is its ordinary mode of
proceeding. At Bournemouth the flies are more active, more difficult to
capture, or have they unmasked the treacherous _Mellinus?_ and is it found
necessary to adopt some fresh contrivance in order to accomplish its ends?
if so, it is not deficient in devices. I noticed once or twice, what I took
to be a dead specimen of _Mellinus_, lying on patches of cow-dung; but on
attempting to pick them up off they flew; I at once suspected the creature,
and had not long to wait before my suspicions were confirmed. Another,
apparently dead fellow, was observed; and there, neither moving head or
foot, the treacherous creature lay, until a fine specimen of a Bluebottle
ventured within its grasp, when, active as any puss, the _Mellinus_ started
into life, and pounced upon its victim."
[Illustration: Fig. 48.—_Mellinus arvensis_ ♀. Britain.]
Lucas states that in the north of France _Mellinus sabulosus_ provisions
its nest with Diptera, which it searches for on the flowers of
Umbelliferae, and then carries to its nest. This is a burrow in the earth,
and when it is reached the Hymenopteron deposits its Insect burden for a
moment on the ground while it turns round in order to enter the burrow
backwards. The same writer states that two varieties of this Insect live
together—or rather in the same colonies—and make use of different species
of Diptera, even of different genera, as food for their young. These
Diptera are stung before being placed in the nest. The stinging does not
kill the Insect, however, for Lucas was able to keep one specimen alive for
six weeks after it had passed this trying ordeal.
SUB-FAM. 8. PHILANTHIDES.—_Labrum small; anterior wings with three
complete submarginal cells; hind body constricted at the base but not so
as to form a slender pedicel._
This sub-family contains Insects resembling wasps or Crabronides in
appearance, and is, as regards the pronotal structure, {125}intermediate
between the two great divisions of the Fossores, for the pronotal lobe
extends nearly or quite as far back as the tegulae, and in _Philanthus_ the
two come into almost actual contiguity.
The species of the genus _Cerceris_ are numerous in Europe, and several of
them are known to make burrows in the ground, and store them with beetles
for the benefit of the future larvae. The beetles chosen differ in family
according to the species of _Cerceris_; but it appears from the
observations of Fabre and Dufour that one kind of _Cerceris_ never in its
selection goes out of the limits of a particular family of beetles, but,
curiously enough, will take Insects most dissimilar in form and colour
provided they belong to the proper family. This choice, so wide in one
direction and so limited in another, seems to point to the existence of
some sense, of the nature of which we are unaware, that determines the
selection made by the Insect. In the case of our British species of
_Cerceris_, Smith observed _C. arenaria_ carrying to its nest Curculionidae
of very diverse forms; while _C. labiata_ used a beetle—_Haltica tabida_—of
the family Chrysomelidae.
[Illustration: Fig. 49.—_Philanthus triangulum_ ♂. Britain.]
The beetles, after being caught, are stung in the chief articulation of the
body, that, namely, between the pro- and mesothorax. _Cerceris
bupresticida_ confines itself exclusively to beetles of the family
Buprestidae. It was by observations on this Insect that Dufour first
discovered the fact that the Insects stored up do not decay: he thought,
however, that this was due to the liquid injected by the wasp exercising
some antiseptic power; but the observations of Fabre have shown that the
preservation in a fresh state is due to life not being extinguished; the
stillness, almost as if of death, being due to the destruction of the
functional activity of the nerve centres that govern the movements of the
limbs.
{126}It has long been known that some species of _Cerceris_ prey on bees of
the genus _Halictus_, and Marchal has recently described in detail the
proceedings of _C. ornata_. This Insect catches a _Halictus_ on the wing,
and, holding its neck with the mandibles, bends her body beneath it, and
paralyses it by a sting administered at the front articulation of the neck.
The _Halictus_ is subsequently more completely stunned or bruised by a
process of kneading by means of the mandibles of the _Cerceris_. Marchal
attaches great importance to this "malaxation"; indeed, he is of opinion
that it takes as great a part in producing or prolonging the paralysis as
the stinging does. Whether the malaxation would be sufficient of itself to
produce the paralysis he could not decide, for it appears to be impossible
to induce the _Cerceris_ to undertake the kneading until after it has
reduced the _Halictus_ to quietude by stinging.
Fabre made some very interesting observations on _Cerceris tuberculata_,
their object being to obtain some definite facts as to the power of these
Insects to find their way home when removed to a distance. He captured
twelve examples of the female, marked each individual on the thorax with a
spot of white paint, placed it in a paper roll, and then put all the rolls,
with their prisoners, in a box; in this they were removed to a distance of
two kilometres from the home and then released. He visited the home five
hours afterwards, and was speedily able to assure himself that at any rate
four out of the twelve had returned to the spot from whence they had been
transported, and he entertained no doubt that others he did not wait to
capture had been equally successful in home-finding. He then commenced a
second experiment by capturing nine examples, marking each with two spots
on the thorax, and confining them in a dark box. They were then transported
to the town of Carpentras, a distance of three kilometres, and released in
the public street, "in the centre of a populous quarter," from their dark
prison. Each _Cerceris_ on being released rose vertically between the
houses to a sufficient height, and then at once passed over the roofs in a
southerly direction—the direction of home. After some hours he went back to
the homes of the little wasps, but could not find that any of them had then
returned; the next day he went again, and found that at any rate five of
the _Cerceris_ liberated the previous day were then at home. This record is
of considerable {127}interest owing to two facts, viz. that it is not
considered that the _Cerceris_ as a rule extends its range far from home,
and that the specimens were liberated in a public street, and took the
direction of home at once.
_Philanthus apivorus_ is one of the best known of the members of this
sub-family owing to its habit of using the domestic honey-bee as the food
for its offspring. In many respects its habits resemble those of _Cerceris
ornata_, except that the _Philanthus_ apparently kills the bee at once,
while in the case of the _Cerceris_, the _Halictus_ it entombs does not
perish for several days. The honey-bee, when attacked by the _Philanthus_,
seems to be almost incapable of defending itself, for it appears to have no
power of finding with its sting the weak places in the armour of its
assailant. According to Fabre, it has no idea of the _Philanthus_ being the
enemy of its race, and associates with its destroyer on amicable terms
previous to the attack being made on it. The _Philanthus_ stings the bee on
the under-surface of the mentum; afterwards the poor bee is subjected to a
violent process of kneading, by which the honey is forced from it, and this
the destroyer greedily imbibes. The bee is then carried to the nest of the
_Philanthus_. This is a burrow in the ground; it is of unusual depth—about
a yard according to Fabre—and at its termination are placed the cells for
the reception of the young; in one of these cells the bee is placed, and an
egg laid on it: as the food in this case is really dead, not merely in a
state of anæsthesia, the _Philanthus_ does not complete the store of food
for its larvae all at once, but waits until the latter has consumed its
first stock, and then the mother-wasp supplies a fresh store of food. In
this case, therefore, as in _Bembex_, the mother really tends the
offspring.
SUB-FAM. 9. MIMESIDES.—_Small Insects with pedicellate hind body, the
pedicel not cylindric; mandibles not excised externally; inner margin of
eyes not concave; middle tibia with one spur; wings with two, or three,
submarginal cells._
Mimesides is here considered to include the Pemphredonides of some authors.
Mimesides proper comprises but few forms, and those known are small
Insects. _Psen concolor_ and _P. atratus_ form their nests in hollow stems,
and the former provisions its nest with Homopterous Insects of the family
Psyllidae. Little {128}information exists as to their habits; but Verhoeff
states that the species of _Psen_—like members of the Pemphredoninae—do not
form cocoons.
The Pemphredonine subdivision includes numerous small and obscure Insects
found chiefly in Europe and North America (Fig. 51, _P. lugubris_); they
resemble the smaller black species of Crabronides, and are distinguished
from them chiefly by the existence of at least two complete, submarginal
cells on the anterior wing instead of one.
[Illustration: Fig. 50.—_Mimesa bicolor_ ♂. Britain.]
The species of _Passaloecus_ live in the burrows that they form in the
stems of plants; _Pemphredon lugubris_ frequents the decayed wood of the
beech. The larva and pupa of the latter have been described by Verhoeff; no
cocoon is formed for the metamorphosis. Both these genera provision their
nests with Aphidae. This is also the case with _Stigmus pendulus_, but the
burrows of this species form a complex system of diverticula proceeding
from an irregular main channel formed in the pithy stems of bushes.
_Cemonus unicolor_, according to Giraud, forms its burrows in
bramble-stems, but it also takes advantage, for the purposes of
nidification, of the abandoned galls of _Cynips_, and also of a peculiar
swelling formed by a fly—_Lipara lucens_—on the common reed, _Arundo
phragmites_. This species also makes use of Aphidae, and Verhoeff states
that it has only an imperfect instinct as to the amount of food it stores.
[Illustration: Fig. 51.—_Pemphredon lugubris_ ♀. Britain.]
SUB-FAM. 10. CRABRONIDES.—_Pronotum short, front wing with one complete
submarginal and two discoidal cells: hind body {129}variable in form,
pedicellate in some abnormal forms, but more usually not stalked._
The Crabronides (_Vespa crabro_, the hornet, is not of this sub-family) are
wasp-like little Insects, with unusually robust and quadrangular head. They
frequently have the hind tibiae more or less thickened, and the clypeus
covered with metallic hair. It appears at present that they are specially
attached to the temperate regions of the northern hemisphere, but this may
possibly be in part due to their having escaped attention elsewhere. In
Britain they form the most important part of the fossorial Hymenoptera, the
genus _Crabro_ (with numerous sub-genera) itself comprising thirty species.
The males of some of the forms have the front tibiae and tarsi of most
extraordinary shapes. They form burrows in dead wood, or in pithy stems,
(occasionally in the earth of cliffs), and usually store them with Diptera
as food for the larvae: the wings and dried portions of the bodies of the
flies consumed by Crabronides are often exposed to view when portions of
old wood are broken from trees.
[Illustration: Fig. 52.—_Crabro cephalotes_ ♀. Britain.]
The genus _Oxybelus_ is included by some systematists, but with doubt, in
this sub-family; if not placed here, it must form a distinct sub-family. It
has the metathorax spinose, and the sub-marginal and first discoidal cells
are not, or are scarcely, separated.
_Crabro leucostomus_ has been observed by Fletcher to form cells for its
larvae in the soft wood of broken willows: the food stored therein consists
of two-winged flies of the family Dolichopodidae. This _Crabro_ is
parasitised by an Ichneumonid of the genus _Tryphon_, and by a two-winged
fly of uncertain genus, but belonging to the family Tachinidae. The
metamorphoses of _Crabro chrysostomus_ have been briefly described by
Verhoeff: the food stored consists of Diptera, usually of the family
{130}Syrphidae; the larva spins an orange-red cocoon, passes the winter
therein, and assumes the pupal form in the spring; there is, he says, a
segment more in the female pupa than there is in the male.
The species of the sub-genus _Crossocerus_ provision their nests with
Aphididae, but _C. wesmaeli_ makes use, for the purpose, according to
Ferton, of an elegant little fly of the family Tipulidae; according to
Pissot this same wasp also makes use of a species of _Typhlocyba_, a genus
of the Homopterous division of Rhynchota. Supposing there to be no mistake
as to this latter observation, the choice of Diptera and of Homoptera by
the same species indicates a very peculiar habit.
_Fertonius_ (_Crossocerus_) _luteicollis_ in Algeria forms cells at a
slight depth in sandy soil, and provisions them with ants. The ant selected
is _Tapinoma erraticum_, and the individuals captured are the wingless
workers. The mode of hunting has been described by Ferton; the wasp hovers
over one of the ant-paths at a distance of a few millimetres only above the
surface, and when an ant that is considered suitable passes, the
_Fertonius_ pounces on it, stings it, and carries it off to the burrow;
forty or fifty ants are accumulated in a cell, the egg is laid in the heap
of victims about one-third of the depth from the bottom; the resulting
larva sucks the ants one by one, by attaching itself to the thorax behind
the first pair of legs. There is a very interesting point in connection
with the habits of this species, viz. that the ants are not only alive, but
lively; they have, however, lost the power of co-ordinating the movements
of the limbs, and are thus unable to direct any attack against the feeble
larva. Ferton thinks there are three generations of this species in a
single year.
* * * * *
Note.—In a note on p. 99 we have mentioned the new publication of Mr. and
Mrs. Peckham on the habits of Fossores. We may here add that it contains
much fresh information on these Insects, together with criticisms of the
views of Fabre and others. One of the points most noteworthy is that they
have observed _Crabro stirpicola_ working night and day for a period of
forty-two consecutive hours. They made experiments on _Bembex spinolae_
with a view of ascertaining whether the female provisions two nests
simultaneously; as the result they think this improbable. If the female
Bembecid make nests only consecutively, it is clear it must have but a
small fecundity. The larval life extends over about fifteen days; and if
we allow three months as the duration of life of a female, it is evident
that only about six young can be produced in a season.
{131}CHAPTER IV
HYMENOPTERA ACULEATA _CONTINUED_—DIVISION IV. FORMICIDAE OR ANTS
DIVISION IV. HETEROGYNA OR FORMICIDAE—ANTS.
_The segment, or the two segments, behind the propodeum, either small or
of irregular form, so that if not throughout of small diameter, the
articulation with the segment behind is slender, and there is great
mobility. The trochanters undivided. The individuals of each species are
usually of three kinds, males, females and workers; the latter have no
wings, but the males and females are usually winged, though the females
soon lose the flying organs. They live in communities of various numbers,
the majority being workers. The larvae are helpless maggots fed and
tended by the workers or by the female._
[Illustration: Fig. 53—Abdomens of ants. A, Of _Camponotus rubripes_
(Formicides); B, of _Ectatomma auratum_ (Ponerides); C, of _Aphaenogaster
barbara_ (Myrmicides). _a_, Propodeum; _b_, first abdominal segment forming
a scale or node; _c_, second; _d_, third abdominal segment.]
In ants the distinction between the three great regions of the body is very
marked. The abdomen is connected with the propodeum in a peculiar manner,
one or two segments being detached from the main mass to form a very mobile
articulation. This is the most distinctive of the characters of ants. The
structure and form of these parts varies {132}greatly in the family: and
the Amblyoponides do not differ in a marked manner from the Scoliidae in
fossorial Hymenoptera.
[Illustration: Fig. 54—Front of head of _Dinoponera grandis_. A, Mouth
closed; B, open.]
The arrangement of the parts of the mouth is remarkable, and results in
leaving the mandibles quite free and unconnected with the other trophi; the
mouth itself is, except during feeding, closed completely by the lower lip
and maxilla assuming an ascending vertical direction, while the upper lip
hangs down and overlaps the lower lip, being closely applied to it; so that
in Ponerides the palpi, except the apices of the maxillary pair, are
enclosed between the upper and lower lips (Fig. 54, A). In Cryptocerini the
palpi are not covered by the closed lips, but are protected by being placed
in chinks at the outsides of the parts closing the mouth. The mandibles of
ants can thus be used in the freest manner without the other parts of the
mouth being opened or even moved. The mandibles close transversely over the
rest of the mouth, and when shut are very firmly locked. There are,
however, some ants in which the lips remain in the position usual in
mandibulate Insects.
The antennae, except in the males of some species, have a long basal joint
and are abruptly elbowed at its extremity. The eyes and ocelli vary
excessively, and may be totally absent or very highly developed in the same
species. The winged forms are, however, never blind. The size of the head
varies extremely in the same species; it is frequently very small in the
males, and largest in the workers. In some ants the worker-caste consists
of large-headed and small-headed individuals; the former are called
soldiers, and it has been supposed that some of them may act the part of
superior officers to the others. It should be clearly understood that there
is no definite distinction between soldiers and workers; so that in this
respect they are widely different from Termites.
{133}[Illustration: Fig. 55—_Oecodoma cephalotes._ South America. A, Worker
major; B, female after casting the wings.]
[Illustration: Fig. 56.—Stridulating organ of an ant, _Myrmica rubra_, var.
_laevinodis_. Sagittal section of part of the 6th and 7th post-cephalic
segments. (After Janet.) _a_, _a^1_, muscles; _b_, connecting membrane
(corrugated) between 6th and 7th segments: _c_, 6th segment; _d_, its edge
or scraper; _e_, striate area, or file on 7th segment; _f_, posterior part
of 7th segment; _g_, cells, inside body; _h_, trachea.]
The complex mass forming the thorax is subject to great change of structure
in the same species, according as the individuals are winged or wingless.
The sutures between the dorsal (notal) pieces are frequently obliterated in
the workers, while they are distinct in the males and females, and the
pieces themselves are also much larger in size in these sexed individuals.
The pro-mesothoracic stigma is apparently always distinct; the
meso-metathoracic one is distinct in the male _Dorylus_, but can scarcely
be detected in the winged forms of other ants, owing to its being enclosed
within, and covered by, the suture between the two segments: in the
workers, however, it is usually quite conspicuous. The posterior part of
the thoracic mass, the propodeum or median segment, is of considerable
size; no transverse suture between the component pieces of this part can be
seen, but its stigma is always very distinct. The peduncle, or pedicel,
formed by the extremely mobile segment or segments at the base of the
abdomen (already noticed as forming the most conspicuous character of the
family), exhibits much variety. Sometimes the first segment bears a plate
or shield called a scale (Fig. 53, A, _b_); at other times there are two
{134}small segments (Fig. 53, B, C, _b_, _c_) forming nodes or knots, of
almost any shape. The articulations between these segments are of the most
perfect description. In many ants these parts bear highly developed
stridulating organs, and the delicacy and perfection of the articulations
allow the parts to be moved either with or without producing stridulation.
In the male sex the peduncle and its nodes are much less perfect, and
possess comparatively little capacity for movement; in the male of
_Dorylus_ (Figs. 79, A, and 80, _f_) the single node is only imperfectly
formed. The eyes and ocelli of the males are usually more largely developed
than they are in the female, though the head is much smaller.
The legs of ants are elongate, except in a few forms; the Cryptocerini and
the males of Dorylides being the most conspicuous exceptions. The tarsi are
five-jointed, the basal joint being disproportionately elongate, so that in
use it acts in many species as if it were a portion of the tibia, the other
four joints forming the functional foot. The front tibiae are furnished
with a beautiful combing apparatus (Fig. 57).
[Illustration: Fig. 57.—Combs and brushes on front leg of an ant,
_Dinoponera grandis_ (tip of tibia, bearing the comb-like spur, and the
base of the first joint of the tarsus; cf. fig. 75). A, Inner, B, outer
aspect.]
FEATURES OF ANT-LIFE.—In order that the reader may realise the nature of
ant-life we may briefly recount its more usual and general features.
Numerous eggs are produced in a nest by one or more queens, and are taken
care of by workers. These eggs hatch and produce helpless maggots, of which
great care is taken by the workers. These nurses feed their charges from
their own mouths, and keep the helpless creatures in a fitting state by
transporting them to various chambers in conformity with changes of
temperature, humidity, and so on. When full grown the maggots change to
pupae. In some species the maggots form cocoons for themselves, but in
others this is not the case, and the pupae are naked.[54] After a brief
period of {135}pupal life a metamorphosis into the perfect Insect occurs.
The creatures then disclosed may be either winged or wingless; the wingless
are the workers and soldiers—imperfect females—the winged are males or
females fully developed. The workers remain in or near the nest they were
produced in, but the winged individuals rise into the air for a nuptial
flight, often in great numbers, and couple. When this is accomplished the
male speedily dies, but the females cast their wings and are ready to enter
on a long life devoted to the production of eggs. From this account it will
be gathered that males are only found in the nests for a very short time;
the great communities consisting at other periods entirely of the two kinds
of females and of young. The imperfect females are themselves in some
species of various kinds; each kind being restricted, more or less
completely, to a distinct kind of duty.
No Insects are more familiar to us than ants; in warm countries some of
them even invade the habitations of man, or establish their communities in
immediate proximity to his dwellings. Their industry and pertinacity have,
even in remote ages, attracted the attention and admiration of serious men;
some of whom—we need scarcely mention Solomon as amongst them—have not
hesitated to point out these little creatures as worthy of imitation by
that most self-complacent of all the species of animals, _Homo sapiens_.
Observation has revealed most remarkable phenomena in the lives of these
Insects. Indeed, we can scarcely avoid the conclusion that they have
acquired in many respects the art of living together in societies more
perfectly than our own species has, and that they have anticipated us in
the acquisition of some of the industries and arts that greatly facilitate
social life. The lives of individual ants extend over a considerable number
of years—in the case of certain species at any rate—so that the competence
of the individual may be developed to a considerable extent by exercise;
and one generation may communicate to a younger one by example the arts of
living by which it has itself profited. The prolonged life of ants, their
existence in the perfect state at all seasons, and the highly social life
they lead are facts of the greatest biological importance, and are those
that we should expect to be accompanied by greater and wider competence
than is usually exhibited {136}by Insects. There can indeed be little doubt
that ants are really not only the "highest" structurally or mechanically of
all Insects, but also the most efficient. There is an American saying to
the effect that the ant is the ruler of Brazil. We must add a word of
qualification; the competence of the ant is not like that of man. It is
devoted to the welfare of the species rather than to that of the
individual, which is, as it were, sacrificed or specialised for the benefit
of the community. The distinctions between the sexes in their powers or
capacities are astonishing, and those between the various forms of one sex
are also great. The difference between different species is extreme; we
have, in fact, the most imperfect forms of social evolution coexisting,
even locally, with the most evolute.
These facts render it extremely difficult for us to appreciate the ant; the
limitations of efficiency displayed by the individual being in some cases
extreme, while observation seems to elicit contradictory facts. About two
thousand species are already known, and it is pretty certain that the
number will reach at least five thousand. Before passing to the
consideration of a selection from what has been ascertained as to the
varieties of form and of habits of ants we will deal briefly with their
habitations and polymorphism, reserving some remarks as to their
associations with other Insects to the conclusion of this chapter.
NESTS.—Ants differ greatly from the other Social Hymenoptera in the nature
of their habitations. The social bees construct cells of wax crowded
together in large numbers, and the wasps do the like with paper; the eggs
and young being placed, each one in a separate cell, the combinations of
which form a comb. Ants have, however, a totally different system; no comb
is constructed, and the larvae are not placed in cells, but are kept in
masses and are moved about from place to place as the necessities of
temperature, air, humidity and other requirements prompt. The habitations
of ants are in all cases irregular chambers, of which there is often a
multiplicity connected by galleries, and they sometimes form a large system
extending over a considerable area. Thus the habitations of ants are more
like those of the Termites than those of their own allies among the
Hymenoptera. They are chiefly remarkable for their great variety, and for
the skilful manner in which they are adapted by their little artificers to
particular conditions. The most usual form in Europe, is a {137}number of
subterranean chambers, often under the shelter of a stone, and connected by
galleries. It is of course very difficult to trace exactly the details of
such a work, because when excavations are made for the purposes of
examination, the construction becomes destroyed; it is known, however, that
some of these systems extend to a considerable depth in the earth, it is
said to as much as nine feet, and it is thought the object of this is to
have access to sufficiently moist earth, for ants are most sensitive to
variations in the amount of moisture; a quite dry atmosphere is in the case
of many species very speedily fatal. This system of underground labyrinths
is sometimes accompanied by above-ground buildings consisting of earth more
or less firmly cemented together by the ants; this sort of dwelling is most
frequently adopted when the soil in which the nests are placed is sandy; it
is probable that the earth is in such cases fastened together by means of a
cement produced by the salivary glands of the ants, but this has not been
determined with certainty; vaulted galleries or tunnels of this kind are
constructed by many species of ants in order to enable them to approach
desired objects.
[Illustration: Fig. 58—Portion of combined nest of _Formica fusca_ and
_Solenopsis fugax_. (After Forel.) × ⅔. _f_, _f′_, Chambers of _Formica_,
recognisable by the coarser shading; _s_, _s′_, chambers of the
_Solenopsis_ (with finer shading); _s″_, opening in one of the chambers,
the entrance to one of the galleries that connects the chambers of the
Solenopsis; _w_, walls forming the foundations of the nest and the limits
of the chambers.]
In South America _Camponotus rufipes_ and other species that habitually
dwell in stumps, in certain districts where they are liable to inundations,
build also nests of a different nature on trees for refuge during the
floods. In Europe, a little robber-ant, _Solenopsis fugax_, constructs its
dwelling in combination with that of _Formica fusca_ (Fig. 58), in such a
manner that its chambers cannot, on account of the small size of the
orifices, be entered by the much larger _Formica_. Hence the robber obtains
an easy living at the expense of the larger species. The Sauba or Sauva
ants of South America (the genus _Atta_ of some, _Oecodoma_ of other
authors) appear to be most proficient in the art of {138}subterranean
mining. Their systems of tunnels and nests are known to extend through many
square yards of earth, and it is said on the authority of Hamlet Clark that
one species tunnelled under the bed of the river Parahyba at a spot where
it was as broad as the Thames at London Bridge.
A considerable number of ants, instead of mining in the ground, form
chambers in wood; these are usually very close to one another, because, the
space being limited, galleries cannot be indulged in. _Camponotus
ligniperdus_ in Europe, and _C. pennsylvanicus_ in North America, work in
this way.
Our British _Lasius fuliginosus_ lives in decayed wood. Its chambers are
said by Forel to consist of a paper-like substance made from small
fragments of wood. _Cryptocerus_ burrows in branches. _Colobopsis_ lives in
a similar manner, and Forel informs us that a worker with a large head is
kept stationed within the entrance, its great head acting as a stopper;
when it sees a nest-fellow desirous of entering the nest, this animated and
intelligent front-door then retreats a little so as to make room for
ingress of the friend. Forel has observed that in the tropics of America a
large number of species of ants live in the stems of grass. There is also
quite a fauna of ants dwelling in hollow thorns, in spines, on trees or
bushes, or in dried parts of pithy plants; and the tropics also furnish a
number of species that make nests of delicate paper, or that spin together
by means of silk the leaves of trees. One eastern species—_Polyrhachis
spinigera_—fabricates a gauze-like web of silk, with which it lines a
subterranean chamber after the manner of a trap-door spider.
[Illustration: Fig. 59—Ant-plant, _Hydnophytum montanum_. Java. (After
Forel.)]
Some species of ants appear to find both food and shelter {139}entirely on
the tree they inhabit, the food being usually sweet stuff secreted by
glands of the plant. It is thought that the ants in return are of
considerable benefit to the plant by defending it from various small
enemies, and this kind of symbiosis has received much attention from
naturalists. A very curious condition exists in the epiphytic plants of the
genera _Myrmecodia_ and _Hydnophytum_; these plants form large bulb-like
(Fig. 59) excrescences which, when cut into, are found to be divided into
chambers quite similar to those frequently made by ants. Though these
structures are usually actually inhabited by ants, it appears that they are
really produced by the plant independent of the Insects.
VARIABILITY AND POLYMORPHISM OF ANTS.—Throughout the Hymenoptera there are
scattered cases in which one of the sexes appears in dimorphic form. In the
social kinds of bees and wasps the female sex exists in two conditions, a
reproductive one called queen, and an infertile one called worker, the
limits between the two forms seeming in some cases (honey-bee) to be
absolute as regards certain structures. This sharp distinction in structure
is rare; while as regards fertility intermediate conditions are numerous,
and may indeed be induced by changing the social state of a community.[55]
In ants the phenomena of the kind we are alluding to are very much more
complex. There are no solitary ants; associations are the rule (we shall
see there are one or two cases in which the association is with individuals
of other species). In correlation with great proclivity to socialism we
find an extraordinary increase in the variety of the forms of which species
are made up. In addition to the male and female individuals of which the
species of Insects usually consist, there are in ants workers of various
kinds, and soldiers, all of which are modified infertile females. But in
addition to the existence of these castes of infertile females, we find
also numerous cases of variability or of dimorphism of the sexual
individuals; and this in both sexes, though more usually in the female.
Thus there exists in ants an extraordinary variety in the polymorphism of
forms, as shown by the table on p. 141, where several very peculiar
conditions are recorded.
The complex nature of these phenomena has only recently {140}become known,
and as yet has been but little inquired into. The difference between the
thoracic structure in the case of the winged and wingless females of
certain species (Fig. 55, and in vol. v. fig. 339) is enormous, but in
other species this difference appears to be much less. The ordinary
distinctions between the queen-female and worker-females appear to be of
two kinds; firstly, that the former is winged, the latter wingless;[56] and
secondly, that the former possesses a _receptaculum seminis_, the latter
does not. In a few cases it would seem that the dimorphism of winged and
wingless forms is not complete, but that variability exists. Intermediate
conditions between the winged and wingless forms are necessarily rare;
nevertheless a certain number have already been detected, and specimens of
_Lasius alienus_ have been found with short wings. In rather numerous
species some or all of the fertile females depart from the usual state and
have no wings; (a similar condition is seen, it will be recollected, in
Mutillides and Thynnides of the neighbouring family Scoliidae). A
dimorphism as regards wings also exists in the male sex, though it is only
extremely rarely in ants that the males are wingless. Neverless a few
species exist of which only wingless males have been found, and a few
others in which both winged and wingless individuals of this sex are known
to occur. The wingless males of course approach the ordinary workers (=
infertile wingless females) in appearance, but there is not at present any
reason for supposing that they show any diminution in their male sexual
characters. The distinction between workers and females as based on the
existence or non-existence of a _receptaculum seminis_ has only recently
become known, and its importance cannot yet be estimated. The adult,
sexually capable, though wingless forms, are called ergatoid, because they
are similar to workers (Ἐργατης, a worker).[57]
{141}TABLE OF THE CHIEF FORMS OF POLYMORPHISM IN ANTS.
OW♂ = Ordinary Winged Male.
E♂ = Ergatoid Male.
OW♀ = Ordinary Winged Female.
EF♀ = Ergatoid Fertile Female.
I♀W = Intermediate between Female and Worker.
Sol = Soldier.
WMj = Worker Major.
WMi = One or more kinds of Worker Minor.
+———————————————————————————+———+———+———+———————+———————+———+—————+—————+
| Name of Ants. |OW♂|E♂ |OW♀| EF♀ | I♀W |Sol| WMj | WMi |
+———————————————————————————+———+———+———+———————+———————+———+—————+—————+
| _Myrmica_, _Polyrhachis_, | + | | + | | | | + | |
| etc. | | | | | | | | |
| | | | | | | | | |
| _Camponotus_, _Atta_, | + | | + | | | | + | + |
| Pheidologeton_, etc. | | | | | | | | |
| | | | | | | | | |
| _Pheidole_, subg. | + | | + | | | + | | + |
| Colobopsis_ | | | | | | | | |
| | | | | | | | | |
| _Eciton hamatum_, | | | | | | | | |
| E. quadriglume_, | + | | | + | | + | + | + |
| E. foreli_, etc. | | | | | | | | |
| | | | | | | | | |
| _Cryptocerus_ | + | | + | | | + | + | + |
| discocephalus_, etc. | | | | | | | | |
| | | | | | | | | |
| _Strongylognathus_ | + | | + | | | + | | |
| | | | | | | | | |
| _Carebara_ and | | | | | | | | |
| Solenopsis_ (except | + | | + | | | | | + |
| S. germinata_) | | | | | | | | |
| | | | | | | | | |
| _Solenopsis geminata_ | + | | + | | | | + | + |
| | | | | | | | | |
| _Formica rufa_ | + | | + | | + | | | |
| | | | | |except-| | | |
| | | | | |ionally| | | |
| | | | | | | | | |
| _Ponera punctatissima_ | + | + | + | | | | + | |
| | | | | | | | | |
| _Ponera ergatandria_ | ? | + | + | | | | + | |
| | | | | | | | | |
| _Cardiocondyla emeryi_ | + | | + | + | | | + | |
| | | | | | | | | |
| _C. wroughtonii_ and | | + | + | | | | + | |
| C. stambuloffi_ | | | | | | | | |
| | | | | | | | | |
| _Formicoxenus nitidulus_ | | + | + | | | | + | |
| | | | | | | | | |
| _Tomognathus_ | + | | | + | | | | |
| | | | | | | | | |
| _Odontomachus haematodes_ | + | | + | + | | | + | |
| | | | |except-| | | | |
| | | | |ionally| | | | |
| | | | | | | | | |
| _Polyergus_ | + | | + | + | | | | |
| | | | | | | | | |
| _Dorylus_, _Anomma_, | + | | | + | | | + | + |
| Eciton_ part. | | | | | | | | |
| | | | | | | | | |
| _Aenictus_ | + | | | | | | | + |
| | | | | | | | | |
| _Leptogenys_, _Diacamma_ | + | | | + | + | | + | |
| | | | | | | | | |
| _Myrmecocystus melliger_, | + | | + | | | | + | |
| M. mexicanus_ | | | | | | | and | + |
| | | | | | | |honey| |
| | | | | | | |-pots| |
| | | | | | | | | |
| | | | | | | | + | + |
| _Ponera eduardi_ | + | | + | | | |eyes |eyes |
| | | | | | | |large|obso-|
| | | | | | | | |lete |
| | | | | | | | | |
| _Anergates_ | | + | + | | | | | |
+———————————————————————————+———+———+———+———————+———————+———+—————+—————+
In addition to the above there are apparently cases of females with
post-metamorphic growth in Dorylides, but these have not yet been the
subject of investigation.
{142}Much has been written about the mode in which the variety of forms of
a single species of ant is produced. As to this there exists but little
actual observation or experiment, and the subject has been much complicated
by the anxiety of the writers to display the facts in a manner that will
support some general theory. Dewitz was of opinion that workers and queens
of ants were produced from different kinds of eggs. This view finds but
little support among recent writers. Hart in recording the results of his
observations on the parasol ant (of the genus _Atta_)—one of the species in
which polymorphism is greatest—says[58] that these observations prove that
"ants can manufacture at will, male, female, soldier, worker or nurse," but
he has not determined the method of production, and he doubts it being "the
character of the food." There is, however, a considerable body of evidence
suggesting that the quality or quantity of the food, or both combined, are
important factors in the treatment by which the differences are produced.
The fact that the social Insects in which the phenomena of caste or
polymorphism occur, though belonging to very diverse groups, all feed their
young, is of itself very suggestive. When we add to this the fact that in
ants, where the phenomena of polymorphism reach their highest complexity,
the food is elaborated in their own organs by the feeders that administer
it, it appears probable that the means of producing the diversity may be
found herein. Wasmann has pointed out that the ants'-nest beetle,
_Lomechusa_, takes much food from the ants, and itself destroys their
young, and that in nests where _Lomechusa_ is abundant a large percentage
of ergatogynous forms of the ants are produced. He attributes this to the
fact that the destruction of the larvae of the ant by the beetle brings
into play the instinct of the ants, which seek to atone for the destruction
by endeavouring to produce an increased number of fertile forms; many
ergatogynous individuals being the result. This may or may not be the case,
but it is clear that the ants' instinct cannot operate without some
material means, and his observation adds to the probability that this means
is the food supply, modified either qualitatively or quantitatively.
The existence of these polymorphic forms led Herbert Spencer to argue that
the form of an animal is not absolutely {143}determined by those "Anlagen"
or rudiments that Weismann and his school consider to be all important in
determining the nature or form of the individual, for if this were the
case, how can it be, he asked, that one egg may produce either a worker,
nurse, soldier or female ant? To this Wasmann (who continued the
discussion) replied by postulating the existence of double, triple or
numerous rudiments in each egg, the treatment the egg receives merely
determining which of these rudiments shall undergo development.[59] Forel
seems to have adopted this explanation as being the most simple. The
probability of Weismann's hypothesis being correct is much diminished by
the fact that the limit between the castes is by no means absolute. In many
species intermediate forms are common, and even in those in which the
castes are believed to be quite distinct, intermediate forms occur as very
rare exceptions.[60] Emery accounts[61] for the polymorphism, without the
assistance of the Weismannian hypothetical compound rudiments, by another
set of assumptions; viz. that the phenomenon has been gradually acquired by
numerous species, and that we see it in various stages of development; also
that variation in nutrition does not affect all the parts of the body
equally, but may be such as to carry on the development of certain portions
of the organisation while that of other parts is arrested. Speaking broadly
we may accept this view as consistent with what we know to be the case in
other Insects, and with the phenomena of post-embryonic development in the
class. But it must be admitted that our knowledge is at present quite
inadequate to justify the formulation of any final conclusions.
The geological record of Formicidae is not quite what we should have
expected. They are amongst the earliest Hymenoptera; remains referred to
the family have been found in the Lias of Switzerland and in the English
Purbecks. In Tertiary times Formicidae appear to have been about the most
abundant of all Insects. At Florissant they occur in thousands and form in
individuals about one-fourth of all the Insects found there. They have also
been met with numerously in the European Tertiaries, and Mayr studied no
less than 1500 specimens found {144}in amber. Formicides and Myrmicides are
more abundant than Ponerides, but this latter group has the larger
proportion of extinct genera; conditions but little dissimilar to those
existing at present.
CLASSIFICATION OF ANTS.—Ants are considered by many entomologists to form a
series called Heterogyna. They can, however, be scarcely considered as more
than a single family, Formicidae, so that the serial name is superfluous.
Their nearest approach to other Aculeates is apparently made, by
_Amblyopone_, to certain Mutillides (_e.g._ _Apterogyna_) and to the
Thynnides, two divisions of Scoliidae. Emery considers Dorylides rather
than Amblyoponides to be the most primitive form of ants, but we are
disposed to consider Forel's view to the effect we have above mentioned as
more probably correct. The point is, however, very doubtful. The condition
of the peduncle is in both the sub-families we have mentioned very
imperfect compared with that of other ants. Both these sub-families are of
very small extent and very imperfectly known. We shall also follow Forel in
adopting six sub-families, Camponotides, Dolichoderides, Myrmicides,
Ponerides, Dorylides, and Amblyoponides. Emery rejects the Amblyoponides as
being merely a division of the Ponerides. This latter group displays the
widest relations of all the sub-families, and may be looked on as a sort of
central form. The Camponotides and Dolichoderides are closely allied, and
represent the highest differentiation of the families in one direction. The
Myrmicides are also highly differentiated, but are not allied to the
Camponotides and Dolichoderides.[62]
SUB-FAM. 1. CAMPONOTIDES.—_Hind body furnished with but one constriction,
so that only a single scale or node exists on the pedicel. Poison-sac
forming a cushion of convolutions, on which is situate the modified
sting, which forms merely an ejaculatory orifice for the poison._
The members of this very extensive division of ants can be readily
distinguished from all others, except the Dolichoderides, by the absence of
a true sting, and by the peculiar form of the hind body; this possesses
only a single scale at the base, and has no {145}constriction at all on the
oval, convex and compact mass of the abdomen behind this. The cloacal
orifice is circular, not, as in other ants, transverse. These characters
are accompanied by a difference in habits. The Camponotides, though they do
not sting, produce poison in large quantity, and eject it to some distance.
Hence, if two specimens are confined in a tube they are apt to kill one
another by the random discharges they make. Janet suggests that in order to
neutralise the effect of this very acid poison, they may have some means of
using, when they are in their natural abodes, the alkaline contents of a
second gland with which they are provided. We shall mention the characters
by which the Camponotides are distinguished from the small sub-family
Dolichoderides when we deal with the latter.
The sub-family includes 800 or more species. _Camponotus_ itself is one of
the most numerous in species of all the genera of Formicidae, and is
distributed over most parts of the earth. We have no species of it in
Britain, but in the south of Europe the _Camponotus_ become very
conspicuous, and may be seen almost everywhere stalking about, after the
fashion of our British wood-ant, _Formica rufa_, which in general
appearance _Camponotus_ much resembles.
Until recently, the manner in which fresh nests of ants were founded was
unknown. In established nests the queen-ant is fed and tended by the
workers, and the care of the helpless larvae and pupae also devolves
entirely on the workers, so that the queens are relieved of all functions
except that of producing eggs. It seemed therefore impossible that a fresh
nest could be established by a single female ant unless she were assisted
by workers. The mode in which nests are founded has, however, been recently
demonstrated by the observations of Lubbock, M‘Cook, Adlerz, and more
particularly by those of Blochmann, who was successful in observing the
formation of new nests by _Camponotus ligniperdus_ at Heidelberg. He found
under stones in the spring many examples of females, either solitary or
accompanied only by a few eggs, larvae or pupae. Further, he was successful
in getting isolated females to commence nesting in confinement, and
observed that the ant that afterwards becomes the queen, at first carries
out by herself all the duties of the nest: beginning by making a small
burrow, she lays some eggs, and when these hatch, feeds and tends the
larvae and pupae; the first specimens of these {146}latter that become
perfect Insects are workers of all sizes, and at once undertake the duties
of tending the young and feeding the mother, who, being thus freed from the
duties of nursing and of providing food while she is herself tended and
fed, becomes a true queen-ant. Thus it seems established that in the case
of this species the division of labour found in the complex community, does
not at first exist, but is correlative with increasing numbers of the
society. Further observations as to the growth of one of these nascent
communities, and the times and conditions under which the various forms of
individuals composing a complete society first appear, would be of
considerable interest.
An American species of the same genus, _C. pennsylvanicus_, the
carpenter-ant, establishes its nests in the stumps of trees. Leidy observed
that solitary females constructed for themselves cells in the wood and
closed the entrances, and that each one in its solitary confinement reared
a small brood of larvae. The first young produced in this case are said to
be of the dwarf caste, and it was thought by the observer that the ant
remained not only without assistance but also without food during a period
of some weeks, and this although she was herself giving food to the larvae
she was rearing.
Adlerz states that the females or young queens take no food while engaged
in doing their early work, and that the large quantity of fat-body they
possess enables them to undergo several months of hunger. In order to feed
the young larvae they use their own eggs or even the younger larvae. It is
to the small quantity of food rather than to its nature that he attributes
the small size of the first brood of perfect workers. M. Janet[63] has
recently designed an ingenious and simple apparatus for keeping ants in
captivity. In one of these he placed a solitary female of _Lasius alienus_,
unaccompanied by any workers or other assistants, and he found at the end
of 98 days that she was taking care of a progeny consisting of 50 eggs, 2
larvae, 5 pupae in cocoons, 5 without cocoons. On the 102nd day workers
began to emerge from the cocoons.[64] From these observations it is evident
that the queen-ant, when she begins her nest, lives under conditions
extremely different from those of the royal state she afterwards reaches.
{147}In many kinds of ants the full-grown individuals are known to feed not
only the larvae by disgorging food from their own mouths into those of the
little grubs, but also to feed one another. This has been repeatedly
observed, and Forel made the fact the subject of experiment in the case of
_Camponotus ligniperdus_. He took some specimens and shut them up without
food for several days, and thereafter supplied some of them with honey,
stained with Prussian blue; being very hungry, they fed so greedily on this
that in a few hours their hind bodies were distended to three times their
previous size. He then took one of these gorged individuals and placed it
amongst those that had not been fed. The replete ant was at once explored
by the touches of the other ants and surrounded, and food was begged from
it. It responded to the demands by feeding copiously a small specimen from
its mouth: when this little one had received a good supply, it in turn
communicated some thereof to other specimens, while the original well-fed
one also supplied others, and thus the food was speedily distributed. This
habit of receiving and giving food is of the greatest importance in the
life-history of ants, and appears to be the basis of some of the
associations that, as we shall subsequently see, are formed with ants by
numerous other Insects.
[Illustration: Fig. 60—_Oecophylla smaragdina._ Worker using a larva for
spinning.]
_Oecophylla smaragdina_, a common ant in Eastern Asia, forms shelters on
the leaves of trees by curling the edges of leaves and joining them
together. In doing this it makes use of an expedient that would not be
believed had it not been testified by several competent and independent
witnesses. The perfect ant has no material with which to fasten together
the edges it curls; its larva, however, possesses glands that secrete a
supply of material for it to form a cocoon with, and the ants utilise the
larvae to effect their purpose. Several of them combine to hold the foliage
in the desired position, and while they do so, other ants come up, each one
of which carries a larva in its jaws, applies the mouth of the larva to the
parts where the cement is required, and makes it disgorge the sticky
{148}material. Our figure is taken from a specimen (for which we are
indebted to Mr. E. E. Green) that was captured in the act of bearing a
larva.
_Formica rufa_, the Red-ant, Wood-ant, or Hill-ant, is in this country one
of the best-known members of the Formicidae. It frequents woods, especially
such as are composed, in whole or part, of conifers, where it forms large
mounds of small sticks, straws, portions of leaves, and similar material.
Although at first sight such a nest may appear to be a chaotic
agglomeration, yet examination reveals that it is arranged so as to leave
many spaces, and is penetrated by galleries ramifying throughout its
structure. These mound-nests attain a considerable size when the operations
of the industrious creatures are not interfered with, or their work
destroyed, as it too often is, by ignorant or mischievous persons. They may
reach a height of three feet or near it, and a diameter of twice that
extent. The galleries by which the heaps are penetrated lead down to the
earth below. From the mounds extend in various directions paths constantly
traversed by the indefatigable ants. M‘Cook observed such paths in the
Trossachs; they proceed towards the objects aimed at in lines so straight
that he considers they must be the result of some sense of direction
possessed by the ants; as it is impossible to suppose they could perceive
by the sense of sight the distant objects towards which the paths were
directed: these objects in the case M‘Cook describes were oak-trees up
which the ants ascended in search of Aphides.
M‘Cook further observed that one of the oak-trees was reached by
individuals from another nest, and that each of the two parties was limited
to its own side of the tree, sentinels being placed on the limits to
prevent the trespassing of an intruder; he also noticed that the ants saw
an object when the distance became reduced to about an inch and a half from
them. This species is considered to be wanting in individual courage; but
when acting in combination of vast numbers it does so with intelligence and
success. It does not make slaves, but it has been observed by Bignell and
others that it sometimes recruits its numbers by kidnapping individuals
from other colonies of its own species. Its nests are inhabited by forty or
fifty species of guests of various kinds, but chiefly Insects. Another ant,
_Myrmica laevinodis_, sometimes lives with it in perfect harmony, and
_Formicoxenus {149}nitidulus_ lives only with _F. rufa_. Amongst the most
peculiar of its dependants we may mention large beetles of the genera
_Cetonia_ and _Clythra_, which in their larval state live in the hills of
the wood-ant. It is probable that they subsist on some of the vegetable
matter of which the mounds are formed. Adlerz has given some attention to
the division of labour amongst the different forms of the workers of ants,
and says that in _F. rufa_ it is only the bigger workers that carry
building and other materials, the smaller individuals being specially
occupied in the discovery of honey-dew and other Aphid products. In
_Camponotus_ it would appear, on the other hand, that the big individuals
leave the heavy work to be performed by their smaller fellows.
The wood-ant and its near allies have been, and indeed still are, a source
of great difficulty to systematists on account of the variation that occurs
in the same species, and because this differs according to locality. Our
European _F. rufa_ has been supposed to inhabit North America, and the
interesting accounts published by M‘Cook of the mound-making ant of the
Alleghanies were considered to refer to it. This Insect, however, is not
_F. rufa_, as was supposed by M‘Cook, but _F. exsectoides_, Forel. It forms
colonies of enormous extent, and including an almost incredible number of
individuals. In one district of about fifty acres there was an Ant City
containing no less than 1700 of these large ant-hills, each one teeming
with life. It was found by transferring ants from one hill to another that
no hostility whatever existed between the denizens of different hills; the
specimens placed on a strange hill entered it without the least hesitation.
Its habits differ in some particulars from those of its European congener;
the North American Insect does not close the formicary at night, and the
inquilines found in its nest are very different from those that live with
_F. rufa_ in Europe. Whether the typical wood-ant occurs in North America
is doubtful, but there are races there that doubtless belong to the
species.
_F. sanguinea_ is very similar in appearance to its commoner congener _F.
rufa_, and is the only slave-making ant we possess in Britain. This species
constructs its galleries in banks, and is of very courageous character,
carrying out its military operations with much tactical ability. It is
perfectly able to live without the assistance of slaves, and very
frequently does so; indeed it {150}has been asserted that it is in our own
islands (where, however, it is comparatively rare) less of a slave-owner
than it is in Southern Europe, but this conclusion is very doubtful. It
appears when fighting to be rather desirous of conquering its opponents by
inspiring terror and making them aware of its superiority than by killing
them; having gained a victory it will carry off the pupae from the nest it
has conquered to its own abode, and the ants of the stranger-species that
develop from these pupae serve the conquerors faithfully, and relieve them
of much of their domestic duties. The species that _F. sanguinea_ utilises
in this way in England are _F. fusca_, _F. cunicularia_, and possibly
_Lasius flavus_. Huber and Forel have given graphic accounts of the
expeditions of this soldier-ant. In the mixed colonies of _F. sanguinea_
and _F. fusca_ the slaves do most of the house-work, and are more skilful
at it than their masters. Adlerz says that one of the slaves will
accomplish twice as much work of excavation in the same time as the
slave-owner; these latter being lazy and fond of enjoyment, while the
slaves are very industrious.
[Illustration: Fig. 61—Head of _Polyergus rufescens_. (After André.)]
_Polyergus rufescens_, an European ant allied to _Formica_, is renowned
since the time of Huber (1810) as the slave-making or Amazon ant. This
creature is absolutely dependent on its auxiliaries for its existence, and
will starve, it is said, in the midst of food unless its servitors are
there to feed it. Wasmann, however, states that _Polyergus_ does possess
the power of feeding itself to a certain extent. Be this as it may, the
qualities of this ant as warrior are superb. When an individual is fighting
alone its audacity is splendid, and it will yield to no superiority of
numbers; when the creatures are acting as part of an army the individual
boldness gives place to courage of a more suitable sort, the ants then
exhibiting the act of retreating or making flank movements when necessary.
If a _Polyergus_ that is acting as a member of a troop finds itself
isolated, and in danger of being overpowered, it has then no hesitation in
seeking safety even by flight. This species is provided with mandibles of a
peculiar nature; they are not armed with teeth, {151}but are pointed and
curved; they are therefore used after the manner of poignards, and when the
ant attacks a foe it seizes the head between the points of these curved
mandibles, and driving them with great force into the brain instantly
paralyses the victim.
Mandibles of this shape are evidently unfitted for the purposes of general
work, they can neither cut, crush, nor saw, and it is not impossible that
in their peculiar shape is to be found the origin of the peculiar life of
_Polyergus_: we find similar mandibles reappearing amongst the aberrant
Dorylides, and attaining a maximum of development in the ferocious
_Eciton_; they also occur, or something like them, in a few aberrant
Myrmicides; and in the male sex of many other ants, which sex exercises no
industrial arts, this sort of mandible is present.
The ants that _Polyergus_ usually attacks in order to procure slaves are
_Formica fusca_ and _F. fusca_, race _auricularia_; after it has routed a
colony of one of these species, _P. rufescens_ pillages the nest and
carries off pupae and some of the larger larvae to its own abode. When the
captives thus deported assume the imago state, they are said to commence
working just as if they were in their own houses among their brothers and
sisters, and they tend their captors as faithfully as if these were their
own relatives: possibly they do not recognise that they are in unnatural
conditions, and may be quite as happy as if they had never been enslaved.
The servitors are by no means deficient in courage, and if the place of
their enforced abode should be attacked by other ant-enemies they defend it
bravely. The fact that _P. rufescens_ does not feed its larvae has been
considered evidence of moral degeneration, but it is quite possible that
the Insect may be unable to do so on account of some deficiency in the
mouth-parts, or other similar cause. The larvae of ants are fed by
nutriment regurgitated from the crop of a worker (or female), and applied
to the excessively minute mouth of the helpless grub: for so delicate a
process to be successfully accomplished, it is evident that a highly
elaborated and specialised arrangement of the mouth-parts must exist, and
it is by no means improbable that the capacity of feeding its young in true
ant-fashion is absent in _Polyergus_ for purely mechanical reasons.
M‘Cook states that the North American ant, _Polyergus lucidus_, which some
entomologists consider to be merely a variety of {152}the European species,
makes slaves of _Formica schaufussi_, itself does no work, and partakes of
food only when fed by its servitors. He did not, however, actually witness
the process of feeding. When a migration takes place the servitors deport
both the males and females of _P. lucidus_. M‘Cook adds that the servitors
appear to be really mistresses of the situation, though they avail
themselves of their power only by working for the advantage of the other
species.
[Illustration: Fig. 62—_Myrmecocystus mexicanus._ Honey-pot ant, dorsal
view.]
[Illustration: Fig. 63—_Myrmecocystus mexicanus._ Lateral view.]
The honey-ant of the United States and Mexico has been investigated by
M‘Cook and others; the chief peculiarity of the species is that certain
individuals are charged with a sort of honey till they become enormously
distended, and in fact serve as leather bottles for the storage of the
fluid. The species _Myrmecocystus hortideorum_ and _M. melliger_, are
moderate-sized Insects of subterranean habits, the entrance to the nest of
_M. hortideorum_ being placed in a small raised mound. The honey is the
product of a small gall found on oak leaves, and is obtained by the
worker-ants during nocturnal expeditions, from which they return much
distended; they feed such workers left at home as may be hungry, and then
apparently communicate the remainder of the sweet stuff they have brought
back to already partly charged "honey-bearers" left in the nest. The
details of the process have not been observed, but the result is that the
abdomens of the bearers become distended to an enormous extent (Figs. 62,
63), and the creatures move but little, and remain suspended to the roof of
a special chamber. It is considered by M‘Cook that these living honey-tubs
preserve the food till a time when it is required for the purposes of
feeding the community. The distension is produced entirely by the
overcharging of the honey-crop, the other contents of the abdomen being
{153}forced by the distention to the posterior part of the body. Lubbock
has since described an Australian ant, _Melophorus inflatus_, having a
similar peculiar habit, but belonging to the allied tribe Plagiolepisii.
Quite recently a South African honey-tub ant belonging to the distinct
genus _Plagiolepis_ (_Ptrimeni_ For.) has been discovered, affording a
proof that an extremely specialised habit may arise independently of
relation between the Insects, and in very different parts of the world.
Species of the genus _Lasius_ are amongst the most abundant of the
ant-tribe in Britain. They are remarkable for their constructive powers.
_L. niger_, the common little black garden-ant, forms extensive
subterranean galleries, and is extremely successful in the cultivation of
various forms of Aphidae, from the products of which the species derives a
large part of its subsistence. The ants even transport the Aphidae to
suitable situations, and thus increase their stock of this sugary kind of
cattle, and are said to take the eggs into their own dwellings in the
autumn so that these minute and fragile objects may be kept safe from the
storms and rigours of winter. These little creatures are brave, but when
attacked by other ants they defend themselves chiefly by staying in their
extensive subterranean galleries, and blocking up and securing these
against their assailants.
_L. fuliginosus_, another of our British species, has very different
habits, preferring old trees and stumps for its habitation; in the hollows
of these it forms dwellings of a sort of card; this it makes from the
mixture of the secretions of its salivary glands with comminuted fragments
of wood, after the fashion of wasps. It is a moderate-sized ant, much
larger than the little _L. niger_, and is of a black colour and remarkably
shining; it gives off a very strong but by no means disagreeable odour, and
may be seen on the hollow trees it frequents, stalking about in large
numbers in a slow and aimless manner that contrasts strikingly with the
active, bustling movements of so many of its congeners. When this species
finds suitable trees near one another, a colony is established in each; the
number of individuals thus associated becomes very large, and as the
different colonies keep up intercommunication, this habit is very useful
for purposes of defence. Forel relates that he once brought a very large
number of _Formica pratensis_ and liberated them at the base of a tree in
which was a nest of _L. fuliginosus_; these latter, finding {154}themselves
thus assaulted and besieged, communicated in some way, information of the
fact to the neighbouring colonies, and Forel soon saw large columns of the
black creatures issuing from the trees near by and coming with their
measured paces to the assistance of their _confrères_, so that the invaders
were soon discomfited and destroyed. Although the European and North
American representatives of the sub-family Camponotides live together in
assemblies comprising as a rule a great number of individuals, and although
the separate nests or formicaries which have their origin from the natural
increase of a single original nest keep up by some means a connection
between the members, and so form a colony of nests whose inhabitants live
together on amicable terms, yet there is no definite information as to how
long such association lasts, as to what is the nature of the ties that
connect the members of the different nests, nor as to the means by which
the colonies become dissociated. It is known that individual nests last a
long time. Charles Darwin has mentioned in a letter to Forel that an old
man of eighty told him he had noticed one very large nest of _Formica rufa_
in the same place ever since he was a boy. But what period they usually
endure is not known, and all these points probably vary greatly according
to the species concerned. It has been well ascertained that when some ants
find their nests, for some unknown reason, to be unsuitable the inhabitants
leave their abodes, carrying with them their young and immature forms, and
being accompanied or followed by the various parasites or commensals that
are living with them. Wasmann and other entomologists have observed that
the ants carry bodily some of their favourite beetle-companions, as well as
members of their own species. Forel observed that after a nest of _Formica
pratensis_ had been separated into two nests placed at a considerable
distance from one another so as to have no intercommunication, the members
yet recognised one another as parts of the same family after the lapse of
more than a month; but another observation showed that after some years of
separation they were no longer so recognised.
Although it is now well ascertained that ants are able to distinguish the
individuals belonging to their own nests and colonies from those that,
though of their own species, are not so related to them, yet it is not
known by what means the recognition is effected; there is, however, some
reason to suppose that it {155}is by something of the nature of odour. One
observer has noticed that if an ant fall into water it is on emerging at
first treated as if it were a stranger by its own friends; but other
naturalists have found this not to be the case in other species. Contact
with corrosive sublimate deprives ants for a time of this power of
recognising friends, and under its influence they attack one another in the
most ferocious mariner.
The nests and colonies of the species of Camponotides we have considered
are all constructed by societies comprising a great number of individuals;
there are, however, in the tropics numerous species that form their nests
on foliage, and some of these contain only a few individuals. The
leaf-nests (Fig. 64) of certain species of _Polyrhachis_ are said to be
formed of a paper-like material, and to contain each a female and about 8
or 10 worker ants. Forel[65] has examined nests of several Indian species,
and finds they differ from those of other ants in consisting of a single
cavity, lined with silk like that of a spider. These nests are further said
to be constructed so as to render them either inconspicuous or like other
objects on the leaves; _P. argentea_ covers its small dwelling with little
bits of vegetable matter, and a nest of _P. rastella_ was placed between
two leaves in such a manner as to be entirely hidden. All the species of
the genus do not, however, share these habits, _P. mayri_ making a
card-nest, like _Dolichoderus_ and some other ants. The species of the
genus _Polyrhachis_ are numerous in the tropics of the Old World.
[Illustration: Fig. 64—Nest of _Polyrhachis_ sp. (After Smith.)]
Forbes noticed that a species of this genus, that makes its paper-like nest
on the underside of bamboo-leaves produces a noise {156}by striking the
leaf with its head in a series of spasmodic taps. The same observer has
recorded a still more interesting fact in the case of another species of
this genus—a large brown ant—found in Sumatra. The individuals were "spread
over a space, perhaps a couple of yards in diameter, on the stem, leaves,
and branches of a great tree which had fallen, and not within sight of each
other; yet the tapping was set up at the same moment, continued exactly the
same space of time, and stopped at the same instant; after the lapse of a
few seconds all recommenced at the same instant. The interval was always of
about the same duration, though I did not time it; each ant did not,
however, beat synchronously with every other in the congeries nearest to
me; there were independent tappings, so that a sort of tune was played,
each congeries dotting out its own music, yet the beginnings and endings of
the musical parties were strictly synchronous."
[Illustration: Fig. 65—_Polyrhachis pandurus_, worker. Singapore.]
Mr. Peal has also recorded that an ant—the name is not mentioned, but it
may be presumed to be an Assamese species—makes a concerted noise loud
enough to be heard by a human being at twenty or thirty feet distance, the
sound being produced by each ant scraping the horny apex of the abdomen
three times in rapid succession on the dry, crisp leaves of which the nest
is usually composed. These records suggest that these foliage-ants keep up
a connection between the members of different nests somewhat after the same
fashion as do so many of the terrestrial Camponotides. Although the species
of Camponotides have no special organ for the production of sound in the
position in which one is found in Myrmicides and Ponerides, yet it is
probable that they are able to produce a sound by rubbing together other
parts of the abdomen.
{157}SUB-FAM. 2. DOLICHODERIDES.—_Hind body furnished with but one
constriction so that only a single scale or node is formed; Sting
rudimentary; the poison-sac without cushion._
[Illustration: Fig. 66—_Tapinoma erraticum_, worker. Britain. Upper side
and profile.]
The Dolichoderides are similar to Camponotides in appearance, and are
distinguished chiefly by the structure of the sting and the poison
apparatus. To this we may add that Forel also considers the gizzard to be
different in the two sub-families, there being no visible calyx in the
Dolichoderides, while this part is largely developed in the Camponotides.
This is one of the least extensive of the sub-families of ants, not more
than 150 species being yet discovered. Comparatively little is known of the
natural history of its members, only a very small number of species of
Dolichoderides being found in Europe. The best known of these (and the only
British Dolichoderid) is _Tapinoma erraticum_, a little ant of about the
size of _Lasius niger_, and somewhat similar in appearance, but very
different in its habits. _T. erraticum_ does not cultivate or appreciate
Aphides, but is chiefly carnivorous in its tastes. Our knowledge of it is
due to Forel, who has noticed that it is very fond of attending the fights
between other ants. Here it plays the part of an interested spectator, and
watching its opportunity drags off the dead body of one of the combatants
in order to use it as food. Although destitute of all power of stinging,
this Insect has a very useful means of defence in the anal glands with
which it is provided; these secrete a fluid having a strong characteristic
odour, and possessing apparently very noxious qualities when applied to
other ants. The _Tapinoma_ has no power of ejecting the fluid to a
distance, but is very skilful in placing this odorous matter on the body of
an opponent by touching the latter with the tip of the abdomen; on this
being done its adversary is usually discomfited. This {158}Insect is
subterranean in its habits, and is said to change its abode very
frequently. _T. erraticum_ occurs somewhat rarely in Britain. Forel has
also noted the habits of _Liometopum microcephalum_, another small European
species of Dolichoderides. It is a tree-ant, and by preference adopts, and
adapts for its use, the burrows made by wood-boring beetles. It forms
extremely populous colonies which may extend over several large trees, the
inhabitants keeping up intercommunication by means of numerous workers. No
less than twelve mighty oaks were found to be thus united into a colony of
this ant in one of the Bulgarian forests. The species is very warlike, and
compensates for the extreme minuteness of its individuals by the skilful
and rapid rushes made by combined numbers on their ant-foes of larger size.
Fritz Müller has given a brief account, under the name of the Imbauba ant,
of a Brazilian arboreal ant, that forms small nests in the interior of
plants. The species referred to is no doubt an _Azteca_, and either _A.
instabilis_, or _A. mulleri_. The nests are founded by fertilised females
which may frequently be found in the cells on young _Cecropia_ plants. Each
internode, he says, has on the outside, near its upper part, a small pit
where the wall is much thinner, and in this the female makes a hole by
which she enters. Soon afterwards the hole is completely closed by a
luxuriant excrescence from its margins, and it remains thus closed until
about a dozen workers have developed from the eggs of the female, when the
hole is opened anew from within by the workers. It is said that many of the
larvae of these ants are devoured by the grubs of a parasite of the family
Chalcididae. This Insect is thought to protect the plant from the attacks
of leaf-cutting ants of the genus _Atta_.
We may here briefly remark that much has been written about the benefits
conferred on plants by the protection given to them in various ways by
ants: but there is reason to suppose that a critical view of the subject
will not support the idea of the association being of supreme importance to
the trees.[66]
SUB-FAM. 3. MYRMICIDES.—_Pedicel of abdomen formed of two well-marked
nodes (knot-like segments). Sting present (absent in the Cryptocerini and
Attini). (It should be noted that the {159}workers of the genera Eciton
and Aenictus of the subfamily Dorylides have, like the Myrmicides, two
nodes in the pedicel.)_
This sub-family consists of about 1000 species, and includes a great
variety of forms, but, as they are most of them of small size, they are
less known than the Camponotides, and much less attention has been paid to
their habits and intelligence. Forel, until recently, adopted four groups:
Myrmicini, Attini, Pseudomyrmini and Cryptocerini; but he is now disposed
to increase this number to eight.[67] They are distinguished by differences
in the clypeus, and in the form of the head; but it must be noted that the
characters by which the groups are defined are not in all cases fully
applicable to the males. The Cryptocerini are in external structure the
most highly modified of Hymenoptera, if not of all the tribes of Insecta.
[Illustration: Fig. 67—_Pheidologeton laboriosus_, large and small workers.
East India.]
i. The Myrmicini proper are defined by Forel as having the antennae
inserted near the middle, a little behind the front, of the head, which has
carinae on the inner sides, but none on the outer sides, of the insertions
of the antennae; the clypeus extends between the antennae.
[Illustration: Fig. 68—_Formicoxenus nitidulus_, male. (After Adlerz.)]
Certain genera of small European ants of the group Myrmicini display some
most anomalous phenomena. This is especially the case in _Formicoxenus_,
_Anergates_ and _Tomognathus_. The facts known have, however, been most of
them only recently discovered, and some obscurity still exists as to many
of even the more important points in these extraordinary life-histories.
{160}[Illustration: Fig. 69.—_Anergates atratulus_. Europe. A, male, with
part of hind leg broken off; B, female, with wings: C, female, after
casting the wings and becoming a queen.]