Chapter VIII: Hemiptera, or Bugs—anoplura 532 (8)

The formicaries are of considerable size, and are described as consisting of low mounds of bare earth of considerable extent. Bates speaks of as great a circumference as forty yards; these accumulations of earth have frequently an appearance different from the adjoining soil, owing to their being formed of subsoil brought up from below; they are kept bare by the ants constantly bringing to and depositing on the surface fresh material resulting from their subterranean excavations. The true abodes, beneath the earth, are of greater extent than the mounds themselves, and extend to a considerable depth; they consist of chambers connected by galleries.

The leaf-cutting ants extend their range to North America, and M‘Cook has recently called attention to a case there in which _A. fervens_ made an underground route at an average depth of 18 inches, and at an occasional depth of 6 feet, extending 448 feet entirely beneath the earth, after which it was continued for 185 feet to reach a tree which the ants were engaged in defoliating. This route, extending altogether to a length of more than 600 feet, presented only a very slight deviation from a straight line drawn between the point of departure and the object to be attained. By what sense this ant was enabled {167}to make a subterranean tunnel in a straight line to a desired object situated at so great a distance, we know not.

The use the leaf-cutting ants make of the enormous amount of material they gather was for long a subject of debate, and has only recently been ascertained by the observations of Möller. After being carried to the nest the pieces of leaves are cut into small fragments by another set of workers and formed into balls, which are packed in various parts of the nest, and amongst which the mycelium of a fungus—_Rozites gongylophora_—ramifies. This fungus the ants cultivate in the most skilful manner: they manage to keep it clear from mouldiness and bacterial agents, and to make it produce a modified form of growth in the shape of little white masses, each one formed by an agglomeration of swellings of the mycelium. These form the chief food of the colony. Möller ascertained by experiment that the results were due to a true cultivation on the part of the ants: when they were taken away from the nests, the mycelium produced two kinds of conidia instead of the ant-food.

Many details of the economy of these leaf-cutting ants are still very imperfectly known. The large-headed forms, called soldiers, have been the subject of contradictory statements; Bates having concluded from his own observations that they are harmless, while Mr. J. H. Hart assures us that they are very fierce and vindictive, and inflict very serious wounds by biting (the Attini do not sting). We anticipate that the observations of both these naturalists will prove to be substantially correct, and that the differences in habits will be found to be owing to distinctions in the conditions of the community. In connection with this point we may remark that the function of the excessively large heads of certain kinds of soldier-ants is still obscure. In the East Indian _Pheidologeton diversus_ the big soldiers are quite one hundred times as large as the smaller workers. As these latter bite viciously it would naturally be supposed that their gigantic _confrères_ with enormous heads would be warriors of a most formidable nature; but, as a matter of fact, the giants are unable to bite even when they try to do so. Aitken has somewhere suggested that these enormous individuals play the part of state elephants; and we have been informed by Colonel Bingham that the small ants may frequently be seen riding in numbers on their unwieldy fellows. We anticipate {168}however, that some other function will be found to exist for these forms with enormous heads. An examination of their organs of sense and of voice is very desirable.

Details of the modes in which the great communities of the leaf-cutting Attidae are maintained, are still wanting. The females do not, we have been informed by Mr. Hart, possess any considerable powers of aftergrowth, so that there is no reason to suppose them to be unusually prolific. At certain seasons great swarms of winged individuals are produced, and after leaving the nests pair in the manner of our European _Myrmica_. Possibly the females may, after losing their wings, again enter the large communities. Von Ihering states that the workers of _Atta lundi_ are fertile.

iii. The group Pseudomyrmini includes the genera _Pseudomyrma_ and _Sima_, which are by some entomologists treated as but a single genus. The antennae are inserted near together on the front of the head; there is no carina on the head external to their insertion, and the clypeus does not extend forwards between them. The Insects are usually of elongate form, possess a sting, and have a naked pupa. The group occurs in both hemispheres, but is exclusively exotic, and but little is known of the habits of its members. Forel has recently observed that numerous species live inside dried stems of grass or in hollow twigs, and are beautifully adapted for this mode of life by their elongate form, some of them being as slender as needles. Some interesting observations have been made in Nicaragua by Belt on _Pseudomyrma bicolor_ and its relations with an acacia-tree, in the thorns of which it lives. The acacia in question is called the bull's-horn thorn, because the branches and trunk are armed with strong curved spines, set in pairs, and much resembling the horns of the quadruped whose name they bear. The ant takes possession of a thorn by boring a small hole near the distal extremity, and forms its nest inside. The leaves of this plant are provided with glands that secrete a honey-like fluid, which it appears forms the chief, if not the sole, subsistence of the ant. Belt considers that the presence of the ant is beneficial to the acacia; he supposes that the ants assume the rights of proprietors, and will not allow caterpillars or leaf-cutting ants to meddle with their property; the leaves are, he thinks, so preserved to the benefit of the tree.

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Rothney has given some particulars of the habits of _Sima rufo-nigra_, an ant of this group that appears to be not uncommon near Calcutta, where it lives on the trunks of trees in company with a spider and a wasp that greatly resemble it in form and in colour. The three creatures seem to associate together on amicable terms; indeed the wasp and the ant occasionally indulge in wrestling matches without doing one another any serious harm. In connection with this fact we may observe that other species of ants have been observed to indulge in sports and feats of agility.

_S. leviceps_, an Australian species of this genus, is furnished with a stridulating file that has the appearance of being constructed so as to produce two very different kinds of sounds.

iv. The Cryptocerini are distinguished from other ants by their antennae being inserted at the sides of the head, where they are placed between ridges or in a groove into which they can be withdrawn; when in some cases they are entirely concealed. These ants assume a great variety of shapes and forms, some of which look almost as if they were the results of an extravagant imagination. The skeleton is usually much harder than it is in other {170}ants; the abdomen consists almost entirely of one very large segment, there being, however, three others visible at its extremity; these segments can be only slightly protruded, and the ants have no power of stinging. They are probably most of them arboreal in their habits. Nearly all of the known forms are exotic. According to the observations of Bates the species of the genus _Cryptocerus_ in the Amazons Valley may frequently be observed in dry open places on low trees and bushes, or running on branches of newly felled trees; they also visit flowers abundantly. The species generally are wood-borers, usually perforating the dead branches of trees. _C. atratus_ has been observed to construct its nests in the dead, suspended branches of woody climbers; a number of neatly drilled holes are all that can be seen externally; but, inside, the wood is freely perforated with intercommunicating galleries. Each community appears to consist of a single female and two kinds of workers; the latter in some species are quite unlike each other, differing in the form of the head, and in the armature of the thorax and nodes of the peduncle. The species of _Cryptocerus_ appear to be omnivorous, and are frequently attracted by the excrement of birds. The pupae are not enclosed in a cocoon. In the South of Europe two very minute ants, of the genera _Strumigenys_ and _Epitritus_, belonging to this family, are met with under very large stones partly embedded in the earth. They are of the greatest rarity.

SUB-FAM. 4. PONERIDES.—_Hind body elongate, furnished with one node at
the base, and having also great capacity of movement between the first
and second segments, between which there is usually a slight
constriction. Sting well developed._

This sub-family includes numerous genera and about 400 species. The Ponerides have an elongate hind-body; the second segment behind the node is capable of great movement in and out of the preceding segment, and for this purpose is furnished with a basal portion slightly more slender than the apical part; this {171}basal part is usually concealed within the more anterior segment, the hind margin of which embraces it very closely. On the middle of the dorsal aspect of this articulation there is usually placed a stridulating organ, consisting of an elongate band or patch of very fine lines; this gives out a sound when the second segment is moved in and out of the first at a time when the posterior edge of the latter is slightly depressed.

We follow Forel in including the Australian bull-dog ants—_Myrmecia_—in Ponerides, as well as the Odontomachi. The former have, however, a definite pedicel, consisting of two nodes (Fig. 76). In the Odontomachi the mandibles are approximate at their bases, being inserted on the middle of the front of the head (Fig. 77).

This sub-family includes a considerable number of species, and is found in all parts of the world. Extremely little is known as to the habits, but the true Ponerides do not, so far as is known, occur in large communities, and it seems probable that they are destitute of the powers of combined action that are so remarkable in the Camponotides, and in some of the Myrmicides and Dorylides. Most of the species that have been described are known by only one sex, so that very little knowledge exists as to the sexual distinctions; but from the little that is known it would appear that the three sexual forms are not so differentiated as they are in most of the Camponotides and Myrmicides.

The species of the genus _Leptogenys_ are believed by Emery and Forel to possess an apterous female. Mr. Perkins has observed that the Hawaiian _L. falcigera_ has workers with different kinds of sting, but no true female. Males of this species are, however, abundant. Wroughton has recently discovered that one member of this genus is of Termitophagous habits, but this is not the case with _L. falcigera_. _Dinoponera grandis_ (Fig. 75) is the largest of the Ponerides, its {172}workers attaining an inch and a quarter in length. This Insect, according to Bates, marches in single file in the thickets at Pará; its colonies consist of a small number of individuals, and are established at the roots of slender trees. The effects of its powerful sting are not so serious as is the case with some of the smaller ants.

In Britain we have only two representatives of the sub-family, viz. _Ponera contracta_, a small ant of dirty-yellow colour, found rarely in the Southern counties, living in moss or under stones. Its colonies consist of only a few individuals; Forel giving fifty as the highest number he has observed. The second species, _P. punctatissima_, presents the almost unique peculiarity of possessing two forms of the male sex, one of them resembling the worker in most of its peculiarities, and in being destitute of wings, while the other is winged, as is usual in male ants. In the island of St. Vincent another species of _Ponera_ has been discovered having an apterous and worker-like male, and was named by Forel _P. ergatandria_.[71] The discovery of this form has led him to express some doubt as to whether _Ponera punctatissima_ has two forms of males; but it seems probable that it really is so, the ergatoid males being produced under somewhat different circumstances from the normal males. We shall subsequently see that _Cardiocondyla_ and a few other Myrmicides exhibit an analogous peculiarity.

The genus _Myrmecia_ is confined to the Australian continent and Tasmania, and includes a considerable number of species of large and moderate-sized ants, the classification of which has been a subject of difference of opinion. This has arisen from the fact that the nodes of the abdominal pedicel are more similar to those existing in the Myrmicides than to those of the typical Ponerides. There are, however, some American members of the latter sub-family (_Paraponera clavata_, _e.g._) that differ but little in this point from _Myrmecia_, and, moreover, the pupae of _Myrmecia_ are enclosed in a cocoon, while in the Myrmicides they are usually naked. On the other hand the nests are, it appears, very large and populous, more like what exists in the Myrmicides; there is no true stridulating organ on the first abdominal segment. The genus is therefore one of those interesting anomalies that form so large a proportion of the Australian {173}fauna, and will probably be ultimately treated as a distinct sub-family. There are about thirty species.

The ants of this genus are well known to the residents in Australia, where they are called "bull-dog ants." They form large mounds of earth for their nests. The workers, and females (Fig. 76) are much alike except during the period when the latter are still carrying their wings. The males, however, differ considerably, being of more slender form, and possessing only insignificant mandibles, and straight antennae with a quite short basal joint.

Forel considers _Myrmecia_ to be the most formidable of all the ants; the hills are said to be sometimes five feet high, and the colonies are immense in numbers, while the Insect is an inch or more in length, and armed with a very powerful sting, the use of which on the human body is said to give rise in some cases to serious symptoms. On the other hand, we have seen statements to the effect that the sting of _Myrmecia_ has only very evanescent sequelae; it is also said that the ant-hills have only a slight elevation, so that probably both these points differ according to the species. It appears from a communication of Miss Shepherd's that the formidable _Myrmecia forficata_ has its larvae destroyed by a parasitic Hymenopteron (_Eucharis myrmeciae_) of brilliant colour and considerable size, so that we have the curious fact of the hordes of this most formidably armed ant, which possesses also large eyes, falling a victim to a brilliant and very conspicuous Insect. Particulars of this case of parasitic attack are still wanting. There are other cases known of the larvae of ants being destroyed by parasitic Diptera and Hymenoptera, but in none of them have any sufficient observations been made as to the mode in which the attack is made. Lowne says that _M. gulosa_ itself attacks large beetles of the genus _Anoplognathus_ and buries them; and he also adds the very curious statement that _M. nigrocincta_, when running, is able to take leaps of a foot in length.

The Odontomachi were formerly considered a distinct sub-family, distinguished by the peculiar mandibles (Fig. 77). {174}Many of the Ponerides have elongate mandibles, but they are inserted at the sides of the front of the head, not in the middle of the front. These organs in some species of Odontomachi serve as levers, by aid of which the Insect can execute considerable leaps. In only a few species are the males known; Mayr and Forel state that they are destitute of the peculiar mandibles characteristic of the worker.

The unique European representative of the Odontomachi, _Anochetus ghiliani_, occurs in Andalusia. Near Tangier Mr. George Lewis found it to be not uncommon; but the sexes are not known, and it even appears doubtful whether there exists any well-marked division between workers and female. Lewis observed, among the ordinary forms, individuals with longer bodies, usually one in a nest, and he supposed these to be females; Saunders, on examining these examples, found them to possess distinct ocelli, and therefore agreed with Lewis as to their being the female sex. Dr. Emery subsequently examined these same specimens, and took what is scarcely a different view, viz. that they are not females but an intermediate form; and he also expressed the opinion that "the true female may not exist." The male of _Anochetus_ is not known. The female of _A. mayri_, a Neotropical species, has rudimentary wings.

SUB-FAM. 5. DORYLIDES.—_Clypeus extremely small, the antennae inserted
very near the front margin of the head. Hind body usually elongate and
subcylindrical, with an imperfect pedicel formed by the constriction of
the back of the first segment, but occasionally there are two nodes in
the workers. Distinctions between the two sexes, and between the workers
and sexed forms, enormous, the queens truly wingless. The females and
workers usually blind, or at any rate destitute of facetted eyes. (In
Ecitonini the antennae are not inserted quite at the front of the head,
and there are two nodes in the pedicel.)_

{175}We have reserved to the end of the ants the consideration of the two groups Dorylides and Amblyoponides, recent investigations having rendered it somewhat doubtful whether they can be maintained as distinct from Ponerides. The chief character of the Dorylides is that the males are much less ant-like in form than they are in the other groups, and that the distinction between the females and workers are enormous. The little that is known as to the males and females of this group suggests the view that these sexes may offer sufficient reason for keeping the Dorylides as a group distinct from the other ants; but it must be admitted that it is very difficult to find satisfactory characters to distinguish the workers of the Dorylides in some cases from the Ponerides, in others (_Eciton_) from the Myrmicides.[72]

The Dorylides are of great interest, for they exhibit the remarkable phenomenon of a nomadic social life, accompanied by imperfect sight in the wanderers. The sub-family includes two apparently distinct groups: (1) the Ecitonini, peculiar to the New World, and having a close relationship with the Myrmicides; and (2) the Dorylini existing chiefly in the eastern hemisphere, and related closely by its workers to the Ponerides and Amblyoponides. (i.) The Ecitonini consist of the species of the genus _Eciton_, the wandering ants of America, and of _Labidus_, which there is now good reason for believing to consist of the males of _Eciton_. The female is still uncertain. The _Eciton_ are nomad ants having no fixed abode, but wandering from place to place in search of prey, and forming temporary resting-places. The {176}species are rather numerous, and the habits of several have been described by Bates, who, however, was not acquainted with some of the most peculiar features in their biology, these having been since revealed by Belt and W. Müller.

These ants are predaceous in their habits, and some of the species travel in vast hordes; they occasionally enter houses and clear them of much of the vermin with which they may be infested. They have no facetted eyes, some of the forms being quite blind, while others have a pair of peculiar lenses in the position normally occupied by the compound eyes. Usually there are two castes of the workers, and in some species these are very different from one another, the mandibles being in the larger form very elongate, cylindrical and unfit for industrial purposes, while the individuals of the smaller caste have the outer jaws shorter, with their edges apposed and coadapted: in other species individuals with mandibles differentiated from the normal form do not exist. The nomad habits of these ants were described by Bates, but the detection of their temporary resting-places was reserved for Belt, who found that, after their plundering raids, they retired to a place of concealment, and there clustered together in a compact mass like a swarm of bees. Belt says: "They make their temporary habitations in hollow trees and sometimes underneath large fallen trunks that offer suitable hollows. A nest that I came across in the latter situation was open at one side. The ants were clustered together in a dense mass, like a great swarm of bees, hanging from the roof, but reaching to the ground below. Their innumerable long legs looked like brown threads binding together the mass, which must have been at least a cubic yard in bulk, and contained hundreds of thousands of individuals, although many columns were outside, some bringing in the pupae of ants, others the legs and dissected bodies of various Insects. I was surprised to see in this living nest tubular passages leading down to the centre of the mass, kept open, just as if it had been formed of inorganic materials. Down these holes the ants who were bringing in booty passed with their prey. I thrust a long stick down to the centre of the cluster and brought out clinging to it many ants holding larvae and pupae."

Turning now to the _Labidus_ question: many American species of this genus have long been known, though all of them {177}by the male sex only. The discoveries (to be subsequently alluded to) made in the Old World as to the relations between the driver ants and _Dorylus_ raised a suspicion that _Labidus_ might be the male of _Eciton_, the distinctions in the two cases being very analogous: this conjecture has been almost proved to be correct by the recent observations of Hetschko and W. Müller. The latter, who observed the temporary nests of _Eciton hamatum_, confirms Belt's statements as to the ants hanging together in clumps, like swarms of bees; he also states that the change from one temporary abode to another takes place at night, though, as is well known, the hunting forays of this ant are carried on in the daytime. The periods of migration appear to be determined by the time at which all the larvae have assumed the pupal state, this at any rate being the time chosen in the case observed by Müller. This naturalist bagged a part of one of the nests by the aid of ether, and found the larger portion to consist of pupae; there were also some larvae and eggs; a specimen of _Labidus_ (_L. burchelli_) was also found on friendly terms with the _Eciton_-workers; and myrmecophilous Coleoptera were discovered. The pupae are enclosed in cocoons. Persistent search failed to reveal any female, but the examination was made under great difficulties. Müller also states that the earliest pupated larvae yield soldiers, the latest the smallest forms of workers. From observations made by Forel on a pupa, it seems probable that a wingless form of male may be found to exist. If therefore, as appears practically certain, _Labidus_ is the winged male of _Eciton_, it is probable also that males of more or less worker-like form exist, as is now known to be the case in some other Formicidae.

We may here notice a peculiar apterous female ant recently described by André under the name of _Pseudodicthadia incerta_. He thought this might prove to be the female of _Eciton-Labidus_; but his description and figure are imperfect, and do not greatly support his idea of a connection between _Eciton_ and _Pseudodicthadia_.

ii. The group Dorylini includes the genus _Dorylus_, which was founded many years ago for Insects very like _Labidus_. As in the case of the American Insect named, males only were known; two or three allied genera, consisting exclusively of individuals of the sex mentioned, were subsequently described. In the {178}regions inhabited by these males numerous species of blind ants are known, but only in the worker form, and were, or still are, referred to genera called _Typhlopone_ and _Anomma_. Nothing that could be considered to be a female pertaining to any of these Insects was discovered until Gerstaecker described under the generic name _Dicthadia_ an extraordinary apterous female ant found in Java, and it was suspected that it might be the long-expected female of the male _Dorylus_ and of the worker _Typhlopone_ or _Anomma_. This remained for many years without confirmation, but in 1880 Trimen announced the discovery in South Africa of an enormous apterous female ant, allied to _Dicthadia_; it had been disinterred from a nest of small red ants believed (wrongly) to be _Anomma_. As _Dorylus_ had been previously found in connection with allied worker ants it has since then been clear that notwithstanding the enormous differences existing between these three forms they may all pertain to one (or to closely allied) species. From this summary the student should understand that he will find in myrmecological literature many references to two or three genera that really belong to one species.

The workers of the Dorylini at present known are without exception quite blind, and are believed to be all of predaceous habits; it is thought by some that they have no fixed abodes, but, like the Ecitonini, frequently change their residence, and it has been suggested that in doing so they make use of the nests of other ants as temporary abodes; all these points are, however, still unsettled, and as there are several genera it is not unlikely that considerable variety will be found to prevail. The driver ants of Africa, belonging to the genus _Anomma_, are in some {179}respects similar to _Eciton_ in habits, as they enter human habitations and cause nearly everything else to quit; it is probable that they are also exclusively carnivorous. Savage detected the nests of _A. arcens_, but the account he has given of them is too vague to permit one to decide whether the assemblages he saw were of a nomad kind. The workers of this species vary greatly in size, and Emery has recently stated that he believes all the supposed species of the genus to be merely varieties of _A. burmeisteri_. The female of the driver ants is still quite unknown. A _Dorylus_ has been ascertained to be the male of _Typhlopone_. The male _Dorylus_ (Figs. 79, A, and 80) is of great interest, for the propodeum is in a more primitive form than it is in any other petiolate Hymenopteron known to us, while at the same time the pronotum and mesonotum are very highly developed. The genus _Typhlatta_ Sm. has been recently identified by Wroughton and Forel as the worker-condition of which _Aenictus_ is the winged male. The genus _Alaopone_ will probably be found to have some species of _Dorylus_ as its male.

The females of the Dorylides are amongst the rarest of Insects, and are also amongst the greatest of natural curiosities. Although worker ants and female ants are merely forms of one sex—the female—yet in this sub-family of ants they have become so totally different from one another in size, form, structure, and habits that it is difficult to persuade oneself they can possibly issue from similar eggs. In the Insect world there are but few cases in which males differ from females so greatly as the workers of Dorylides do from the females, the phenomena finding their only parallel in the soldiers and females of Termites; the mode in which this difference is introduced into the life of the individuals of one sex is unknown. The largest of all the Dorylides are the African Insects of the genus _Rhogmus_. Only the male is known.

{180}The specimens of female Dorylides that have been detected may, after fifty or sixty years of research, be still counted on the fingers. As the greatest confusion exists in entomological literature owing to the forms of a single species having been described as two or three genera, the following summary of the principal names of genera of Dorylides may be useful:—

_Eciton_ = the workers, _Labidus_ = male: ♀ unknown.

_Pseudodicthadia_: female only known, possibly that of _Eciton_.

_Cheliomyrmex_: workers and soldiers only known.

_Aenictus_ = the male, _Typhlatta_ = worker: ♀ unknown.

_Rhogmus_: male; female unknown. (According to Emery the worker is very
small and like _Alaopone_.)

_Anomma_: only worker known; male probably a _Dorylus_.

_Dorylus_ = male; _Dicthadia_ = ♀: _Alaopone_ and _Typhlopone_ = workers.

SUB-FAM. 6. AMBLYOPONIDES.—_Abdomen destitute of distinct pedicel; the
articulation between the first and second segments behind the true
petiole being broad._

We follow Forel in separating _Amblyopone_ and a few allies from the Ponerides, because the abdominal pedicel is more imperfect than in any other ants. It is, indeed, very difficult to frame a definition that will include the Amblyoponides among ants, and at the same time separate Formicidae and Scoliidae. Forel considers the Amblyoponides to approach closely to certain divisions of the Scoliidae (Thynnides, _e.g._). Little is known of these Insects, though they are widely distributed. _Amblyopone_ is found in Australia and New Zealand; the allied genus _Stigmatomma_ has a wide distribution, occurring even in Europe. The social life is believed to be imperfect, and the habits subterranean and sedentary. The males and females are winged; the latter much resemble the workers, which are nearly blind, and have a considerable general resemblance to _Anomma_ in Dorylides.

ASSOCIATION OF ANTS WITH OTHER KINDS OF INSECTS.—We have already alluded to the fact that a few species of ants are {181}used by other species as attendants, and that the two kinds then live together quite amicably; and we have also seen that a few ants live in association with other species on terms that are not yet understood. One little ant, _Formicoxenus nitidulus_, lives only in the large nests of _Formica rufa_; these ants tolerate the little _Formicoxenus_, which so far as is known does them neither good nor harm. There are also a considerable number of species of small ants that are in the habit of choosing the neighbourhood of larger species for their dwelling-places; in some cases the nests are constructed actually within a portion of the edifice of the more powerful species, and the rule then appears to be that these neighbours do not molest one another. Notwithstanding the militant lives that many of them lead, ants cannot be considered as of generally ferocious disposition.

But the most remarkable point in connection with their toleration consists in the fact that the nests of many species are inhabited by quite a colony of foreign Insects of various Orders; many of these, being found nowhere else, are spoken of as ants'-nest or Myrmecophilous Insects.[73] The relations of ants with other Insects are of the most varied and complex character; some of their guests live with them on terms of the most intimate association, being indeed absolutely dependent for their existence on the good offices of their hosts; others of the ants'-nest Insects are enemies, while others are neutral or indifferent to the ants. We have already mentioned that the guests migrate in company with their hosts.

Many species of ants derive a considerable portion of their sustenance from the sweet substances excreted by Aphidae. Ants may constantly be seen occupied with clusters of Aphidae, and it is said that the ingenious little creatures defend from enemies the manufacturers of the sweet-stuff they are so fond of, even going so far as to form barricades and covered places for the isolation and protection of this peculiar kind of cattle; a few ants keep some of the root-feeding Aphidae in their nests. Coccidae and other Homoptera, which also excrete much matter of a sugary nature, are likewise consorted with by ants; as are also the larvae of some butterflies of the family Lycaenidae; these latter being believed to furnish to the ants some substance of a nutritious kind.

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The Insects we have spoken of are, however, rather of the nature of ant-cattle, and the fondness of the ants for them is not very remarkable. The relations of the ants to the peculiar species of Insects that live only in or around their nests are much more extraordinary. The greater number of these guests belong to the Order Coleoptera, and of these there are many hundreds—probably many thousands—of species that depend on ants for their existence. The family Pselaphidae furnishes a large number of ants'-nest beetles, and it appears probable that most of them excrete some sugary substance of which the ants are fond. Many of these Pselaphidae are of the most fantastic shapes, more especially the members of the sub-family Clavigerides. But the most curious of all the ant's-nest beetles are the Paussidae, a family exclusively dependent on ants, and having the curious faculty, when disturbed, of bombarding—that is, of discharging a small quantity of vapour or liquid in a state of minute subdivision accompanied by a detonation. Many species of _Staphylinidae_ are peculiar to ant's-nests, and most of them are indifferent or inimical to their hosts, but some of them, such as _Atemeles_ (Fig. 82) and _Lomechusa_, are doubtless producers of sweet stuff that is liked by the ants. The ants feed some of their special favourites amongst these guests in the same manner as they feed one another, viz. by opening the mouth, causing a drop of liquid to appear on the lip, and remaining passive while the guest partakes of the proffered _bonne bouche_. This way of giving food to other individuals is a most remarkable feature in the character of ants; it is not the same system that they adopt in feeding the larvae, for they then make a series of actual movements, and force the nutriment into the mouths of the grubs. Besides the Insects we have mentioned there are also Orthoptera, Hemiptera, Poduridae and Thysanura, Acari, and small Isopod crustaceans that live exclusively in company with ants. We have mentioned that a few Hymenopterous and Dipterous parasites have been detected living at the expense of ants; it is probable that closer observation of the ant larvae and pupae in their nests {183}will disclose a greater number of the parasites of this latter class.

Much attention has been given to the relations between ants and their guests by Wasmann.[74] He arranges them in four categories; 1, "Symphily" for the true guests, which are fed and tended by the ants, the guests often affording some substance the ants delight in; 2, "Metochy," the class of tolerated guests, being so far as is known not disagreeable to the hosts; 3, "Synecthry," including those Insects, etc., to which the ants are hostile, but which nevertheless maintain themselves in the midst of their foes; 4, Parasites, dwelling in the bodies of the adult, or of the young ants. Many of these ants'-nest Insects present a more or less perfect resemblance to the ants in one or more points, such as sculpture, colour, size, or form. To these resemblances Wasmann attaches great importance. We should, too, notice that some of the inquilines[75] have become acquainted with the movements and habits of the ants, and stroke them (as the ants do one another) to induce them to disgorge food in the manner we have alluded to. According to Janet, ants of the genus _Lasius_ are infested by Acari of the genus _Antennophorus_. The ants carry the mites, which assume positions so as not to cause greater inconvenience than is inevitable. Moreover, the ants give food to the mites when requested, and behave in a most obliging way to them, though there is not any reason for supposing that in this case the ants derive any benefit from the Symphily.

The relations between ants and plants have been of late years much discussed. We have already briefly alluded to the subject when speaking of the Pseudomyrmini. We will here only remark that ants frequent plants not only for the purpose of securing the sweet stuff excreted by the Aphidae that live on them, but also for the sake of getting the sweet products the plants themselves afford. Mr. Aitken, speaking of ants in India, says: "I have come to the conclusion that one of the most important sources of food-supply which ants have is the sacchariferous glands to be found at the bases of so many leaves." It is supposed that the ants are on the whole beneficial to the plants that thus afford them supply; and this fact is considered by many to afford an adequate explanation of the existence of these interesting relations.

{184}CHAPTER V

COLEOPTERA—OR BEETLES

ORDER V. COLEOPTERA.

_Apparently wingless Insects when at rest, but really with four wings;
the elytra, or anterior pair, shell-like, reposing on the back of the
body and fitted together accurately along the middle by a straight
suture; the posterior pair membranous, folded together under the elytra.
Mouth with mandibles; lower lip not divided along the middle.
Metamorphosis great and very abrupt; the larva being a grub or maggot,
which changes to a pupa (usually soft) in which the external structure of
the perfect Insect is conspicuous._

Coleoptera—or Beetles—are chiefly distinguished from other Insects by the solidity of their external integument, and by the peculiar nature of the first pair of their alar organs, which do not serve as instruments of flight, but as shells for protecting the upper face of the after-body, which, unlike the other parts, remains as a rule soft and membranous. These modifications of structure, though apparently slight, must be really extremely advantageous, for beetles are the predominant Order of Insects in the existing epoch. They depart from most other Insects in being less aerial in their habits; therefore, notwithstanding their enormous numbers, they do not meet the eye so frequently as flies, bees, or butterflies. The parts of the hard outer skeleton are beautifully fitted together, and as their modifications are easily appreciated they offer as fascinating a subject for study as do the skeletons of Vertebrata. The habits of beetles are so extremely varied that it is but little exaggeration to say that Coleoptera are to be found everywhere, when looked for. The number of species at present known is probably about 150,000. Of these somewhere about 3300 have been found in Britain.

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The structure of the hard parts of the skeleton is of importance, as the classification of this enormous number of species is entirely based thereon; it will be readily understood from the accompanying diagram (Fig. 83). The general proportions of the chief parts of the body call for a few remarks. The prothorax is remarkably free, and is therefore capable of a much greater amount of movement independent of the after-body than it is in other Insects. The mesothorax is, on the other hand, much reduced; its chief function in the higher forms is to support the elytra, and to help to keep them together by means of its scutellum. The metathorax, on the contrary, is largely developed, except in the rather numerous forms that are entirely deprived of powers of flight. The composition of the abdomen has been a subject of great difference of opinion. Its upper surface is usually entirely covered by the elytra; the parts visible on the lower surface are called ventral segments, and are usually five in number. Although these five plates may constitute all that is superficially visible of the abdomen, yet if the elytra are taken off it is found that a larger number of segments—usually seven or eight—are visible on the dorsum. This seeming discrepancy of number between the {186}dorsal and ventral plates is due to two facts; 1, that the hind coxae have a great and complex development, so that they conceal the true base of the venter, which, moreover, remains membranous to a greater or less extent, and thus allows much mobility, and at the same time a very accurate coadaptation between the hard parts of the venter and the metasternum[76]; 2, that the terminal segments are withdrawn into the interior of the body, and are correspondingly much modified, the modification being greater in the case of the ventral than in that of the dorsal plates. The anatomy of the parts of the abdomen that are not externally visible has not been adequately studied by coleopterists, but Verhoeff has inaugurated a careful study of the comparative anatomy of the terminal segments[77]; unfortunately, however, he has not so thoroughly studied the modifications at the base, and as it is not clear that these are so uniform as he has taken for granted, it is possible that his numbering of the segments may have to be in some cases modified. The retracted plates or segments are so intimately connected with the internal copulatory organs that it is no easy matter to interpret them. For the nomenclature of these parts we must refer the student to Verhoeff's later works. He considers the abdomen as composed of ten segments, the dorsal plates being demonstrable, while the tenth ventral plate is usually absent. The anal orifice is placed immediately beneath the tenth dorsal plate, and above the genital orifice, which lies behind and above the ninth ventral plate. Peytoureau admits a diversity in both the number of segments and the position of the orifice. These studies in comparative anatomy are surrounded with difficulties, and no morphological conclusions based on them can be considered as final until they have been confirmed by observation of the development of the parts.

The elytra—or wing-cases—frequently have a remarkable sculpture, the use of which is unknown. According to Hofbauer there are between the outer and inner layers, glands secreting a {187}fluid that reaches the surface through small pores. Hicks supposed that he detected nerve cells. Meinert is of opinion that the elytra correspond to the tegulæ of Hymenoptera rather than to the wings of other Insects, but the little evidence that exists is not favourable to this view. The two elytra are usually, in repose, very perfectly fitted together by a complete coadaptation along the middle of the body, so that it is difficult to separate them; this line of junction is called the suture. There are forms in which the coadaptation is quite imperfect (Malacodermidae) and some in which it does not exist at all (_Meloë_). The wings proper of beetles correspond to the posterior pair in other Insects, and are much more irregular in nervuration than those of most other Insects, correlative, it is supposed, with the folding they are subjected to in order to get them beneath the wing-cases. There are large numbers of species, genera, and groups of genera, all the members of which have the wings so much reduced in size as to be quite useless for purposes of flight. These forms are called apterous, though they are not really so, for the elytra (which are really the anterior wings) are present, and even the posterior wings are not truly absent in these cases, though they are sometimes so extremely rudimentary as to elude all but the most careful observation. The number of forms in which the elytra are absent is extremely small; this condition occurs only in the female sex; it is usually confined to cases in which the female is larva-like in form; but in the extraordinary Mediterranean Lamellicorn genus, _Pachypus_, the females are destitute of wings and elytra, though the anterior parts of the body are normally formed: these individuals live underground and rarely or never emerge. When the wings are absent the elytra are frequently soldered; that is to say, united together along the suture by some sort of secondary exudation; this union occurs in every degree of firmness, and appears to be variable in the individuals of one species; probably in accordance with the age of the individual. In most beetles the elytra are not only themselves closely connected, but are also very accurately coadapted with the sides of the body, except at the tip. Sometimes a coadaptation occurs between the tips of the elytra and the body, but not at the tip of the latter. In such cases one or more dorsal plates are left exposed: the last of such exposed dorsal plates is termed pygidium; a similar plate anterior to the pygidium is called propygidium.

{188}LARVAE.—Owing to the difficulty of rearing Coleoptera, less is perhaps known of their life-histories than of those of other Insects. They exhibit, however, extreme diversity correlative with the great specialisation of so many beetles to particular kinds of life. Most beetles must have exactly the right conditions to live in. The larvae of many forms are known. They are composed of a head, three thoracic segments (usually very distinct), and a number of abdominal segments varying from eight to ten. Coleopterous larvae are usually described as having nine abdominal segments; and it is but rarely that ten can be readily detected; they are, however, visible in various forms, as is the case in the form figured (Fig. 84). A great many of them possess a peculiar pseudopod at the underside of the body near or at the extremity; it can in many cases be entirely retracted into the body, and is generally described as being the protruded termination of the alimentary canal. Inspection of a series of larvae shows that it represents a body segment: it is sometimes armed with hooks. Three pairs of small thoracic legs are often present, but are very often completely absent. These thoracic legs may be present in the young larva, but not in the older (_Bruchus_). The usual number of spiracles is nine pairs, one prothoracic, eight abdominal; but this is subject to many exceptions, and mesothoracic and metathoracic stigmata are occasionally found. The figures we give in the following pages will enable the student to form some idea of the variety of form exhibited by beetle larvae.

Pupation usually takes place in a cavity in the earth, or near the feeding-place, but a great many species form a cocoon, composed either of fragments of earth or of wood, and slightly cemented together. A few suspend themselves by the tail after the manner of butterfly caterpillars (Cassididae, Coccinellidae). The pupae are usually extremely soft, their appendages not being fastened to the body. But some pupae (Staphylinides) are truly obtected, having a hard shell and the rudimentary appendages fastened by exudation to the body, like Lepidopterous pupae, and others (Coccinellidae) are intermediate {189}between this state and the normal soft pupa. The pupal state lasts but a short time, from one to three weeks being the usual period. The perfect Insect is at first soft and almost colourless, and it is often some days before it attains its complete coloration and hardness.

CLASSIFICATION.—Owing to the hardness of the skeleton, beetles shrivel but little after death, so that the form and relations of the various sclerites can usually be detected with ease. These sclerites seem to be remarkably constant (except in the case of sexual distinctions) within the limits of each species, and are very useful for the formation of genera and groups of genera; but they vary so much outside the limits mentioned that it is very difficult to make use of them for defining the larger groups. Hence it is not easy to frame accurate definitions of the families, and still less so to arrange these families in more comprehensive series. The natural difficulty has been much increased by the habit coleopterists have of framing their definitions on what is visible without the aid of dissection. Nevertheless considerable progress has been made. We are obliged at present to adopt upwards of eighty families; and we are able to distinguish on positive characters five series; this leaves a large number of forms still unclassified, and these we have here associated as a sixth series, which we have called Coleoptera Polymorpha. This series corresponds with the two series called in books Clavicornia and Serricornia. As it is admitted to be impossible to define these two series, we think it much better to act accordingly, and to establish for the present a great group that can only be characterised by the fact that its members do not belong to any of the other five series. No doubt a larger knowledge of development, coupled with the advance of comparative anatomy, will ultimately bring about a better state of affairs. The Strepsiptera, with one family Stylopidae, are only provisionally included among the Coleoptera. These six series are fairly equal as regards extent. Though the Polymorpha includes the larger number of forms, yet a large part of them belong to four great families (Staphylinidae, Buprestidae, Elateridae, Malacodermidae), which are easily recognisable, so that the number of unmanageable forms is not really great. Indeed, an acquaintance with the external anatomy of two or three dozen species, selected as typical, would enable a student to classify {190}with tolerable certainty the vast majority of species that he would subsequently meet with.

Series 1. _Lamellicornia._—Antennae with the terminal joints leaf-like
(or broader than the others, if not actually leaf-like), and capable of
separation and of accurate apposition. Tarsi five-jointed.

Series 2. _Adephaga_—(_Caraboidea_ of some authors).—Antennae never
lamelliform, thin at the end; all the tarsi five-jointed, with the fourth
joint quite distinct. Maxillae highly developed, with the outer lobe
slender and divided into two segments so as to be palpiform. Abdomen with
six (or more) ventral segments visible.

Series 3. _Polymorpha._—Antennae frequently with either a club, _i.e._
the distal joints broader [Clavicorn series of authors], or the joints
from the third onwards more or less saw-like, the serrations being on the
inner face [Serricorn series of authors]; but these and all the other
characters, including the number of joints in the feet, very variable.

Series 4. _Heteromera._—Front and middle tarsi five-jointed, hind tarsi
four-jointed. Other characters very variable.

Series 5. _Phytophaga._—Tarsi four-jointed [apparently], but with a small
additional joint at the base of the fourth joint: sole usually densely
pubescent [sometimes the feet are bare beneath or bristly, and
occasionally the small joint at the base of the fourth joint is more
distinct].

Series 6. _Rhynchophora._—Head prolonged in front to form a beak; gula
indistinguishable. [Palpi usually not evident.] Tarsi four-jointed
[apparently], but with a very minute additional joint at the extreme base
of the fourth joint.

_Strepsiptera_ (see p. 298).

The first and second series, with much of the third, form the Pentamera, the fifth and sixth the Tetramera [or Pseudotetramera[78]]. The term Isomera was applied by Leconte and Horn to a combination of series 1, 2, 3, and 5.

SERIES 1. LAMELLICORNIA.

_Tarsi five-jointed; antennae with the terminal joints (usually three,
sometimes more), broader on one side, so as to form a peculiar club, the
leaves of which are movable, and in repose are more or less perfectly
coadapted so as to have the appearance of being but one piece._

This series includes three families, Passalidae, Lucanidae, and Scarabaeidae; the latter includes an enormous majority of the species, and in them the structure of the antennae characteristic of the series is well developed; but in the other two families {191}the form of the antennae is not so widely different from that of other Coleoptera. The larvae live on decaying vegetable matter, roots or dung. They have three pairs of legs, and are thick clumsy grubs with curved bodies, the last two segments being of larger size than usual. Many of them possess organs of stridulation, and the structure of their spiracles is very peculiar, each one being more or less completely surrounded by a chitinous plate. The spiracles usually form a system entirely closed, except at the moment when the skin is shed and the tracheal exuviae are detached. Meinert[79] considers these spiracles to be organs of hearing. The life of the larvae is passed underground or in the decaying wood on which the Insect feeds.

Most of the members of this series are remarkable on account of the great concentration of the nerve-centres. This is extreme in _Rhizotrogus_, where there are only two great ganglia, viz. the supra-oesophageal and a great ganglion situate in the thorax, and consisting of the conjoined infra-oesophageal, thoracic, and abdominal ganglia. According to Brandt[80] there are several distinct forms of concentration in the series; the Lucanidae only participate in it to the extent that the perfect Insects exhibit fewer ganglia than the larvae; the latter possess two cephalic, three thoracic, and eight abdominal ganglia, while the perfect Insect has the abdominal ganglia reduced in number to six, and {192}they are placed partially in the thorax. The diminution in number takes place in this case by the amalgamation of the first two abdominal with the last thoracic ganglia.