Chapter VIII: Hemiptera, or Bugs—anoplura 532 (6)

_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._

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.

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."

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.

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.

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.

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.

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._

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.

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}

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).

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.

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.

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.