It has long been known that the little _Formicoxenus nitidulus_ lives as a

guest in the nests of _Formica rufa_, the wood-ant; and another similar

ant, _Stenamma westwoodi_, which shares the same life, was declared by

Nylander and Smith to be its male; it was however shown some years ago by

André that this is a mistake, and that _S. westwoodi_ is really the male of

another ant that had till then been called _Asemorhoptrum lippulum_. This

correction left the workers and females of _Formicoxenus nitidulus_

destitute of a male, but Adlerz has recently discovered that the male of

this species is wingless and similar to the worker, the female being a

winged Insect as usual. It is very curious that the characters by which the

male is distinguished from the worker should vary in this species; but

according to Adlerz this is the case, individuals intermediate in several

points between the males and workers having been discovered. This

phenomenon of quite wingless males in species where the female is winged is

most exceptional, and is extremely rare in Insects; but it occurs, as we

shall see, in one or two other Myrmicides. Charles Darwin made the very

reasonable suggestion that winged males may be developed occasionally as an

exceptional phenomenon, and it is very probable that this may be the case,

though it has not yet been demonstrated. _Formicoxenus nitidulus_ occurs in

England in the nests of _Formica rufa_ and of _F. congerens_, but we are

not aware that the male has ever been found in this country. The genus

_Anergates_ is allied to _Formicoxenus_, and occurs in Central Europe, but

has not been found in Britain; the female, as in _Formicoxenus_, is winged

and the male wingless, but there is no worker-caste; the male is a rather

helpless creature, and incapable of leaving the nest. The species lives in

company with _Tetramorium caespitum_ a little ant very like _Myrmica_, and

not uncommon in South-East England. The female _Anergates_ is at {161}first

an active little creature with wings, but after these are lost the body of

the Insect becomes extremely distended as shown in Fig. 69, C; the creature

is in this state entirely helpless, and as there are no workers, the

_Anergates_ is completely dependent, for the existence of itself and its

larvae, on the friendly offices of the _Tetramorium_ that lives with it.

The mode of the association of these two Insects is at present both

unparalleled and inexplicable, for only workers of the _Tetramorium_ are

found in company with the ♂ and ♀ _Anergates_; the community, in fact,

consisting of males and females of one species and workers of another. The

nests of _Anergates_ are so rare that only a few naturalists have been able

to observe them (Schenk, von Hagens, and Forel may be specially mentioned),

but in the spots where they occur, nests of the _Tetramorium_, containing

all the forms of that species, are numerous, and it therefore seems

probable that a young fertile female of the _Anergates_ may leave a nest in

which it was born, enter a nest of the _Tetramorium_, and, destroying the

queen thereof, substitute herself in the place of the victim; but if this

be really the case, the larvae and pupae of the _Tetramorium_ must also be

destroyed, for no young of the _Tetramorium_ are ever found in these

strange associations. It is very difficult to believe that the

_Tetramorium_ workers should be willing to accept as their queen a creature

that commenced her acquaintance with them by destroying their own queen or

queens and a number of their young sisters; especially as the _Tetramorium_

is a more powerful ant than the _Anergates_, and could readily dispose of

the murderous intruder if it were disposed to do so. It is known, however,

that colonies of _Tetramorium_ completely destitute of queens sometimes

occur, and Wasmann has suggested that the female _Anergates_ may seek out

one of these, and installing herself therein as a substitute, may be

accepted by the orphaned colony. This plausible hypothesis has still to be

verified.

The genus _Cardiocondyla_ also exhibits the phenomenon of apterous,

worker-like males, while in one species, _C. emeryi_, a winged male is also

known to exist.

_Tomognathus sublaevis_ is a little Myrmicid ant, found rarely in Denmark

and Sweden, where its habits have recently been studied by Adlerz. A band

of the _Tomognathus_ attack the nest of another little Myrmicid,

_Leptothorax acervorum_, and succeed by their own pertinacity and the fears

of the _Leptothorax_ in {162}obtaining possession of it; the legitimate

owners disappear, leaving the _Tomognathus_ in possession of their larvae

and pupae; these complete their development only to find themselves the

slaves of _Tomognathus_. The subsequent relations of the two ants are

friendly, the slaves even preventing their masters from wandering from the

nest when they wish to do so. If an established mixed community of this

nature is in want of additional servitors, the _Tomognathus_ secure a

supply by raids after the fashion of the Amazon-ant, bringing back to their

abode larvae and pupae of _Leptothorax_ to be developed as slaves. It was

formerly supposed that the _Tomognathus_ continued its species by perpetual

parthenogenesis of the workers, for neither males nor females could be

found. Adlerz[68] has, however, now discovered the sexual individuals. The

male is an ordinary winged ant, and is so like that sex of the

_Leptothorax_, that Adlerz had failed to distinguish the two before he

reared them. The females are apterous, and in fact like the workers. It

would perhaps be more correct to say that the workers of this species vary

greatly but never become winged; some of them have ocelli and a structure

of the thorax more or less similar to that of winged females, though none

have been found with wings. Certain of these females possess a receptaculum

seminis, and Adlerz treats this as the true distinction between female and

worker. In accordance with this view the female of _Tomognathus_ may be

described as a worker-like individual possessing a receptaculum seminis,

and having more or less of the external structures of winged females,

though never being actually winged. It is probable that other workers

reproduce parthenogenetically. The males of this species will not unite

with females from the same nest, thus differing from many other ants, in

which union between individuals of the same nest is the rule. Finally, to

complete this curious history, we should remark that the larvae of the

_Tomognathus_ are so similar to those of the _Leptothorax_ that Adlerz is

quite unable to distinguish the two.

_Strongylognathus testaceus_ and _S. huberi_ live in association with

_Tetramorium caespitum_, and are cared for by these latter ants; it is

notable that as in the case of the slave-making _Polyergus rufescens_ the

mandibles of the _Strongylognathus_ are cylindrical and pointed, and

therefore unsuitable for industrial occupations. {163}_S. testaceus_ is a

weak little ant, and lives in small numbers in the nests with _T.

caespitum_, which it is said to greatly resemble in appearance. The

proportions of the forms of the two species usually associated is peculiar,

there being a great many workers of _T. caespitum_ both in the perfect and

pupal states, and also all the sexes of the _Strongylognathus_, of which,

however, only a few are workers. This would seem to suggest that _S.

testaceus_ attacks and pillages the nests of _T. caespitum_ in order to

carry off worker pupae, just as _Polyergus rufescens_ does. But the facts

that _S. testaceus_ is a weaker Insect than the _Tetramorium_, and that

only a few of its worker-caste are present in a community where there are

many workers of the _Tetramorium_, seem to negative the view that the

latter were captured by the former; and the mode in which the associated

communities of these two species are started and kept up is still therefore

in need of explanation.

_Strongylognathus huberi_ is a much stronger Insect than its congener, _S.

testaceus_, and Forel has witnessed its attack on _Tetramorium caespitum_.

Here the raid is made in a similar manner to that of _Polyergus rufescens_

on _Formica_; the _Tetramorium_ is attacked, and its pupae carried off to

the abode of the _Strongylognathus_ to serve in due time as its slaves. The

mandibles of _S. huberi_, being similar in form to those of _Polyergus

rufescens_ are used in a similar manner.

Although _T. caespitum_ is common enough in South-East England, it is to be

regretted that none of the guests or associates we have mentioned in

connection with it occur in this country. It is a most variable species,

and is distributed over a large part of the globe.

Our British species of Myrmicides, about ten in number, all belong to the

group Myrmicini; none of them are generally common except _Myrmica rubra_,

which is a most abundant Insect, and forms numerous races that have been

considered by some entomologists to be distinct species; the two most

abundant of these races are _M. ruginodis_ and _M. scabrinodis_, which

sometimes, at the time of the appearance of the winged individuals, form

vast swarms.

The tiny _Monomorium pharaonis_ is a species that has been introduced into

Britain, but now occurs in houses in certain towns; it sometimes

accumulates on provisions in such numbers as to be a serious nuisance.

Seventeen thousand {164}individuals weigh 1 gramme, and it is probable that

a nest may include millions of specimens.

The genus _Aphaenogaster_[69] and its immediate allies include the

harvesting ants of Europe and North America: they form subterranean nests

consisting of isolated chambers connected by galleries; some of the

chambers are used as store-houses or granaries, considerable quantities of

corn, grass, and other seeds being placed in them. _A. structor_ and _A.

barbarus_ have been observed to do this in Southern Europe, by Lespès,

Moggridge, and others.

[Illustration: Fig. 70—_Aphaenogaster (Messor) barbarus._ Algeria. A, male;

B, winged female; C, large worker or soldier; D, small worker. × 3/2.]

In the deserts about Algeria and Tunis a harvesting ant, _Aphaenogaster

(Messor) arenarius_, is an important creature: its subterranean dwellings

are very extensive, and are placed at a depth of several feet from the

surface. Entrance to these dwellings is obtained by small holes, which are

the orifices of galleries many feet in length: the holes are surrounded by

pellets of sand projecting somewhat above the general surface, and

consequently making the places conspicuous. The subterranean works occupy

an area of fifty or a hundred square yards excavated at a depth of three to

six feet. In these immense nests there exists a form of worker, of very

small size, that never comes to the surface.[70]

_Pogonomyrmex barbatus_ and other species have been observed to do

harvesting in North America. After the workers of _P. barbatus_ have taken

the seeds into the nest they separate the husks and carry them out,

depositing them on a heap or {165}kitchen-midden, formed near by. M‘Cook

has witnessed and described the process of stripping the seeds.

Certain genera—e.g. _Aphaenogaster_, _Pheidole_—exhibit great disparity in

the forms of the workers, some of which are of size much superior to the

others, and possess disproportionately large heads; these large individuals

are found in the same nest as the smaller forms. All the intermediate forms

may frequently be found, and at the same time, in the genus

_Aphaenogaster_; but in _Pheidole_ intermediates are of the utmost rarity.

The genus _Cremastogaster_ is remarkable on account of the shape of the

hind body and its articulation, which give the abdomen the appearance of

being put on upside down. This mode of articulation may allow the Insect to

threaten its enemies when they are in front of it; but it is doubtful

whether the _Cremastogaster_ possesses an effective sting.

[Illustration: Fig. 71—_Cremastogaster tricolor_, worker. A, with abdomen

extended; B, uplifted.]

ii. The group Attini is distinguished by the presence of a carina near the

eye, by the antennae being inserted at a moderate distance from one

another, by the clypeus being prolonged backwards between them; and by the

absence of a sting. The group is not represented in Europe, but in Tropical

America the ants belonging to it are amongst the most important of natural

objects. The species of the genus _Atta_ (usually styled _Oecodoma_) are

the formidable leaf-cutting ants of America. They occur in enormous

colonies in certain places, and will in a short time completely strip a

tree of its leaves. As they appear to prefer trees of a useful kind,

especially those planted by man, their ravages are often of the most

serious nature. The natives, feeling it hopeless to contend with these

Insect hordes, only too frequently abandon all attempts to cultivate the

trees and vegetables the Insects are fond of. Both Bates and Belt have

{166}given accounts of some points in the economy of these ants. They are

amongst the largest of the Formicidae, the females in some cases measuring

about two and a half inches across their expanded wings; the males are much

smaller, but are less dissimilar to their partners than is usual among

ants. The workers, on the other hand, are so extremely different, that no

one would suppose them to be at all related to the males and females (see

vol. v. Fig. 339).

The mode of operation of these ants is to form paths from their formicary

extending for a considerable distance in various directions, so that they

have a ready access to any spot in a district of considerable extent; when

a tree or bush is found bearing leaves suitable for their purposes, the

worker ants ascend it in large numbers and cut up the leaves by biting out

of them pieces similar in size and shape to a small coin; these pieces are

then carried back in the jaws of the ants to their nests; the ant-paths are

therefore constantly traversed by bands of little creatures carrying

burdens homewards, or hurrying outwards in search of suitable trees.

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.

{169}[Illustration: Fig. 72—_Sima rufo-nigra_ and its associates. A, winged

female; B, worker, of the ant; C, _Rhinopsis ruficornis_; a fossorial wasp

of the sub-family _Ampulicides_; D, a spider, _Salticus_ sp. The coloration

is extremely similar in all these creatures.]

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.

[Illustration: Fig. 73—Stridulating file of _Sima leviceps_.]

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.

[Illustration: Fig. 74—_Cyrptocerus atratus_, worker. Amazons. The

compressed first joint of the hind foot is shown at _a_ and _b_ in

different positions.]

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.

[Illustration: Fig. 75—_Dinoponera grandis_, worker. Amazons.]

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.

[Illustration: Fig. 76—_Myrmecia pyriformis._ Australia. Female after

casting wings.]

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.

[Illustration: Fig. 77—_Anochetus ghiliani_, worker. Tangier.]

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]

[Illustration: Fig. 78—Various forms of worker of _Eciton hamatum_.

Guatemala.]

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.

[Illustration: Fig. 79—_Dorylus helvolus._ Africa. A, male; B, female

(_Dicthadia_); C, worker major (_Typhlopone_); D, worker minor. (After

Emery.)]

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.

[Illustration: Fig. 80—Body of male of _Dorylus_ sp. Delagoa Bay. _a_,

pronotum; _b_, _c_, divisions of mesonotum; _d_, metanotum; _e_, propodeum;

_f_, first abdominal segment; _g_, _h_, points of insertion of anterior and

posterior wings.]

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._

[Illustration: Fig. 81—_Amblyopone_, worker. Tasmania.]

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.

{182}[Illustration: Fig. 82—The beetle, _Atemeles_, soliciting food from an

ant. (After Wasmann.)]

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.

{185}[Illustration: Fig. 83—Under-surface of a beetle, _Harpalus

caliginosus_; legs and antenna of one side, and some parts of the mouth

removed. A, antenna; B, mandible; C, labrum; D, ligula; E, paraglossa; F,

labial palp; G, inner lobe of maxilla; H, outer lobe (palpiform) of

maxilla; I, maxillary palp; K, mentum; L, gena; M, gula; N, buccal fissure;

V, plates of ventral segments. 1, Prosternum; 2, prosternal episternum; 3,

prosternal epimeron; 4, anterior and middle coxal cavities; 5, inflexed

side of pronotum; 6, mesosternum; 7, mesosternal episternum; 8, mesosternal

epimeron; 9, metasternum; 10, posterior division of metasternum or

ante-coxal piece; 11, metasternal episternum; 12, metasternal epimeron; 13,

epipleuron or inflexed margin of elytron; 14, ventral or ambulatory setae;

15, trochanter; 16, posterior coxa; 17, femur; 18, tibia; 19, tarsus.

(Modified from Leconte and Horn.)]

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.

[Illustration: Fig. 84—Larva of a beetle, Family Cerambycidae (? _Aromia

moschata_). The first spiracle is placed just at the hind margin of the

large prothoracic segment. (From La Massane.)]

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.

[Illustration: Fig. 85.—Antennae of Lamellicorns. 1, _Neleus interruptus_;

2, _Lucanus cervus_ ♂; 3, _Phanaeus splendidulus_ ♀; 4, _Phileurus didymus_

♀; 5, _Polyphylla fullo_ ♂.]

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.

[Illustration: Fig. 86—View of one side of meso- and metathorax of a

Passalid larva from Borneo showing the stridulating organs. _a_, _b_,

Portions of the metathorax; _c_, coxa of 2nd leg; _d_, striate or

stridulating area thereon; _e_, basal part of femur of middle leg; _f_,

hairs with chitinous process at base of each; _g_, the diminutive 3rd leg

modified for scratching the striated area. × 20.]

FAM. 1. PASSALIDAE.—_Labrum large, mobile; mentum deeply cut out in the

middle for the accommodation of the ligula; the lamellae of the antenna

brought together by the curling up of the antenna. The elytra entirely

cover the dorsal surface of the abdomen._ There are four or five hundred

species of this family known; they are usually shining-black, unattractive

beetles, of large size, and are abundant in the decaying wood of tropical

forests. They are quite absent from Europe, and there is only one species

in the United States of North America. The larvae are very interesting,

from the fact that they appear to have only four legs. This arises from the

posterior pair being present only as very short processes, the function of

which is to scrape striated areas on the preceding pair of legs and so

produce sound. In the species figured (Fig. 86) this short leg is a

paw-like structure, bearing several hard digits; but in other species it is

more simple, and without the digits. The perfect Insect has no

sound-producing organs, and it is very remarkable therefore to find the

larvae {193}provided with highly-developed stridulatory structures. No

auditory organ is known, unless the peculiar spiracles be such.

[Illustration: Fig. 87—Head and prothorax of forms of the male of a

stag-beetle; _Homocoderus mellyi_ (Africa). A, Large, B, intermediate, C,

small forms. (From a photograph by R. Oberthür.)]

FAM. 2. LUCANIDAE (_Stag-beetles_).—_Labrum indistinct, fixed; mentum not

excised; antennae not curled in repose, with but little coadaptation of the

terminal joints; the elytra entirely cover the dorsal surface of the

abdomen._ The Stag-beetles are well known on account of the extraordinary

development of the mandibles in the male sex, these organs being in some

cases nearly as long as the whole of the rest of the Insect, and armed with

projections or teeth that give the Insects a most formidable appearance. So

far as we have been able to discover, these structures are put to very

little use, and in many cases are not capable of being of service even as

weapons of offence. The males are usually very much larger than the

females, and are remarkable on account of the great variation in the

stature of different individuals of the same species; correlative with

these distinctions of individual size we find extreme differences in the

development of the head and mandibles. Moreover, the small male specimens

exhibit not merely reductions in the size of the mandibles, but also show

considerable differences in the form of these parts, due, in some cases,

apparently to the fact that only when a certain length of the mandible is

attained is there any development of certain of the minor projections: in

other cases it is not possible to adopt this view, as the small mandibles

bear as many projections as the large forms do, or even more. In each

species these variations fall, in the majority of cases, into distinct

states, so that entomologists describe them as "forms," the largest

developments being called teleodont, the smallest priodont; the terms

mesodont and amphiodont being applied to intermediate states. Leuthner, who

has examined many specimens, states that in _Odontolabis sinensis_, no

intermediates between the teleodont and mesodont forms occur, and as the

{194}two forms are very different they are liable to be mistaken for

distinct species.

There are at present between 500 and 600 species of stag-beetles known; the

Indo-Malayan and Austro-Malayan regions being richest in them. Australia

possesses many remarkable and aberrant forms. In the Ceratognathini—a group

well represented in New Zealand as well as in Australia—the structure of

the antennae is like that of the Scarabaeidae, rather than of the

Lucanidae. The most aberrant form known is, however, our common

_Sinodendron cylindricum_; this departs in numerous features from other

Lucanidae, and instead of the mandibles of the male being more largely

developed, there is a horn on the head; it is very doubtful whether this

Insect should be allowed to remain in the family. Little is known of the

habits and development of Lucanidæ, except in the case of three or four

species that are common in Europe.

[Illustration: Fig. 88—_Sinodendron cylindricum._ A, Larva; B, pupa. New

Forest.]

The common stag-beetle, _Lucanus cervus_, is our largest British beetle.

The larva much resembles that of _Melolontha vulgaris_, but attains a

larger size, and the anal aperture is placed longitudinally instead of

transversely; it lives in decaying wood, or eats the roots of trees without

being injurious; its life in this state lasts about four years; the pupal

period is passed through rapidly, and the perfect Insect may remain for

months underground before it becomes active; this occurs in June and July.

This larva stridulates by scraping certain hard tubercular ridges on the

third pair of legs, over a specially adapted rough area at the base of the

second pair.

The Passalidae and Lucanidae are united by some authorities as a group

called Pectinicornia; the term Lamellicornia being then confined to the

Scarabaeidae. The Passalidae appear, however, to be really more nearly

allied to the Scarabaeidae than to the Lucanidae.

FAM. 3. SCARABAEIDAE (_Chafers_).—_The leaflets of the antennae are well

coadapted, and are susceptible of separation. The elytra {195}usually leave

the pygidium uncovered. The number of visible ventral segments is usually

six, or at the sides seven, not five, as in Lucanidae and Passalidae._ This

is one of the most important families of Insects. About 13,000 species are

already known; as some of them are highly remarkable creatures on account

of the males being armed with horns, they are figured in many works on

natural history. There is great variety of form, and the following five

sub-families may be adopted, though authorities are by no means agreed as

to the classification of this extensive family, which, moreover, be it

remarked, is increasing by the discovery of about 300 new species every

year.

Abdominal spiracles placed in a line on the connecting membranes, and

entirely covered by the wing-cases (Laparosticti).

Sub-fam. 1. COPRIDES.[81]

Abdominal spiracles placed almost in a line, but only the basal three on

the connecting membranes; the terminal one usually not covered by the

wing-cases. Sub-fam. 2. MELOLONTHIDES.

Abdominal spiracles placed in two lines, the basal three on the

connecting membranes, the others on the ventral segments (Pleurosticti).

The claws of the tarsi unequal. Sub-fam. 3. RUTELIDES.

The claws of the tarsi equal; the front coxae transverse, but little

prominent in the descending axis. Sub-fam. 4. DYNASTIDES.

The claws of the tarsi equal; the front coxae more prominent, shorter

transversely. Sub-fam. 5. CETONIIDES.

i. The Coprides form an immense group of about 5000 species; they differ

somewhat in habits from other Lamellicorns, inasmuch as most of them live

on dung, or decaying animal matter; the sub-family connects with the

Lucanidae, so far as superficial characters go, by means of two of its

groups, Trogini and Nicagini, the latter being very near to the

Ceratognathini in Lucanidae. So little is known as to the morphology and

development of these groups that it is not possible to pronounce an opinion

as to the validity of this apparent alliance. _Trox_ stridulates by rubbing

two raised lines on the penultimate dorsal segment across two striate ribs

on the inner face of the elytra; _Geotrupes_, on the other hand, produces

an audible sound by rubbing together a file on the posterior coxa and a

fine ridge on the contiguous ventral segment. The larva in this genus has a

different organ {196}for stridulation from the imago; it is placed on the

second and third pairs of legs, the latter pair being much reduced in size.

The most interesting division of the Coprides is the group Scarabaeini. No

member of this group inhabits the British islands, but in Southern Europe,

and in still warmer lands, these Insects are well known from the curious

habit many of the species have of rolling about balls of dung and earth.

The long hind legs are chiefly used for this purpose, and it is on the

peculiar structure of these limbs that the group has been established. Many

of the stone Scarabaei found in Egyptian tombs represent some kind of

Scarabaeini, and it has been said that the ancient Egyptians looked on

these Insects as sacred because of their movements. These must certainly

appear very strange to those who see them and are unacquainted with their

object. It is stated that the dwellers in the valley of the Nile thought

the actions of these Insects, when rolling their balls, were typical of the

planetary and lunar revolutions; and that the sudden appearance of the

beetles after a period of complete absence was emblematic of a future life.

Many accounts have been given of the habits of members of this group, but

according to Fabre all are more or less erroneous; and he has described the

habits and life-history of _Scarabaeus sacer_ (Fig. 89), as observed by him

in Southern France. These Insects act the part of scavengers by breaking up

and burying the droppings of cattle and other animals. The female

_Scarabaeus_ detaches a portion of the dung and forms it into a ball,

sometimes as large as the fist; this it rolls along by means of its hind

legs, by pushing when necessary with its broad head, or by walking

backwards and dragging the ball with its front legs. The strength and

patience displayed by the creature in the execution of this task are

admirable. Frequently the owner of this small spherical property is joined,

so Fabre informs us, by a friend, who is usually of the same sex and

assists her in pushing along the ball till a suitable place is reached.

When this is attained, the owner commences to excavate a chamber for the

reception of the ball; sometimes the false friend takes advantage of the

opportunity thus offered and carries off the ball for her own use. Should

no disappointment of this sort occur, the _Scarabaeus_ accomplishes the

burying of the ball in its subterranean chamber, and accompanies it for the

purpose of devouring it; the feast is continued without intermission till

the food is entirely {197}exhausted, when the _Scarabaeus_ seeks a fresh

store of provender to be treated in a similar manner. According to M.

Fabre's account these events occur in the spring of the year, and when the

hot weather sets in the _Scarabaeus_ passes through a period of quiescence,

emerging again in the autumn to recommence its labours, which are now,

however, directed immediately to the continuance of the species; a larger

subterranean chamber is formed, and to this retreat the beetle carries dung

till it has accumulated a mass of the size of a moderate apple; this

material is carefully arranged, previous to the laying of the egg, in such

a manner that the grub to be hatched from the egg shall find the softest

and most nutritive portions close to it, while the coarser and more

innutritious parts are arranged so as to be reached by the grub only after

it has acquired some strength; lastly, a still more delicate and nutritive

paste is prepared by the mother beetle for a first meal for the

newly-hatched grub, by some of the food being submitted to a partial

digestion in her organs; finally, the egg is deposited in the selected

spot, and the chamber closed. Certain of the Coprides exhibit, according to

Fabre, some extremely exceptional features in their life-histories. The

mother, instead of dying after oviposition, survives, and sees the growth

of her young to the perfect state, and then produces another generation. No

similar case can be pointed out in Insects, except in the Social kinds; but

from these the Coprides observed by Fabre differ profoundly, inasmuch as

the number of eggs produced by the mother is extremely small; _Copris

hispanus_, for instance, producing in each of its acts of oviposition only

one, two, or three eggs.

[Illustration: Fig. 89—_Scarabaeus sacer._ Portugal.]

{198}ii. The Melolonthides are probably almost as numerous as the Coprides,

some 4000 species being already known. The larvae are believed to feed

chiefly on roots. _Melolontha vulgaris_, the common cockchafer, is very

abundant in some parts of Europe, and owing to this and to the great damage

it causes, has attracted much attention. The memoir by Straus-Durckheim[82]

on its anatomy is one of the classical works of Entomology. This Insect is

so injurious in some parts of France that money is paid by the local

authorities for its destruction. M. Reiset informs us that under this

arrangement 867,173,000 perfect cockchafers, and 647,000,000 larvae were

destroyed in the Seine-inférieure in the four years from the middle of 1866

to 1870. Unlike the Coprides, the larval life in Melolonthides is

prolonged, and that of the imago is of brief duration. In Central Europe

the life-cycle of the individual in _M. vulgaris_ occupies three years,

though in dry periods it may be extended to four years. In Scandinavia the

time occupied by the development appears to be usually five years. The

fertile female enters the ground and deposits its eggs in two or three

successive batches of about fifteen each. The eggs swell as the development

of the embryo progresses; the larva emerges about five weeks after the eggs

have been deposited, and is of relatively large size. When young the larvae

can straighten themselves out and crawl, but when older they lose this

power, and when above ground rest helplessly on their sides. In the winter

they descend deeply into the earth to protect themselves from frost. The

pupa state lasts only a few days, but after the final transformation the

perfect Insect may remain motionless for as much as eight months

underground before commencing its active life in the air.[83] In the

perfect state the Insect is sometimes injurious from the large quantity of

foliage it destroys. Schiödte[84] considered that these larvae (and those

of numerous other Scarabaeidae) stridulate by rubbing certain projections

on the stipes of the maxilla against the under-surface of the mandible.

These surfaces appear, however, but little adapted for the purpose of

producing sound.

iii. The Rutelides number about 1500 species; there are many {199}Insects

of brilliant metallic colours amongst them, but very little is known as to

their life-histories. The larvae are very much like those of Melolonthides.

iv. The Dynastides are the smallest division in number of species, there

being scarcely 1000 known; but amongst them we find in the genera

_Dynastes_ and _Megasoma_ some of the largest of existing Insects. The

horns and projections on the heads and prothoraces of some of the males of

these Insects are truly extraordinary, and it does not appear possible to

explain their existence by any use they are to their possessors. These

structures are but little used for fighting. Baron von Hügel informs the

writer that in Java he has observed large numbers of _Xylotrupes gideon_;

he noticed that the males sometimes carry the females by the aid of their

horns; but this must be an exceptional case, for the shape of these

instruments, in the majority of Dynastides, would not allow of their being

put to this use. The development of these horns varies greatly in most of

the species, but he did not find that the females exhibited any preference

for the highly armed males. The fact that the males are very much larger

than the females, and that the armature is usually confined to them,

suggests, however, that some sexual reason exists for these remarkable

projections. Many Dynastides possess organs of stridulation, consisting of

lines of sculpture placed so as to form one or two bands on the middle of

the propygidium, and brought into play by being rubbed by the extremities

of the wing-cases. This apparatus is of a less perfect nature than the

structures for the same purpose found in numerous other beetles. We have no

member of this sub-family in Britain, and there are scarcely a dozen in all

Europe. Decaying vegetable matter is believed to be the nutriment of

Dynastides. The European _Oryctes nasicornis_ is sometimes found in numbers

in spent tan. The growth and development of the individual is believed to

be but slow.

v. The Cetoniides are renowned for the beauty of their colours and the

elegance of their forms; hence they are a favourite group, and about 1600

species have been catalogued. They are specially fond of warm regions, but

it is a peculiarity of the sub-family that a large majority of the species

are found in the Old World; South America is inexplicably poor in these

Insects, notwithstanding its extensive forests. In this sub-family the mode

of flight is peculiar; the elytra do not extend down the {200}sides of the

body, so that, if they are elevated a little, the wings can be protruded.

This is the mode of flight adopted by most Cetoniides, but the members of

the group Trichiini fly in the usual manner. In Britain we have only four

kinds of Cetoniides; they are called Rose-chafers. The larvae of _C.

floricola_ and some other species live in ants' nests made of vegetable

refuse, and it is said that they eat the ants' progeny. Two North American

species of _Euphoria_ have similar habits. The group Cremastochilini

includes numerous peculiar Insects that apparently have still closer

relations with ants. Most of them are very aberrant as well as rare forms,

and it has been several times observed in North America that species of

_Cremastochilus_ not only live in the nests of the ants, but are forcibly

detained therein by the owners, who clearly derive some kind of

satisfaction from the companionship of the beetles. The species of the

genus _Lomaptera_ stridulate in a peculiar manner, by rubbing the edges of

the hind femora over a striate area on the ventral segments.

SERIES II. ADEPHAGA OR CARABOIDEA.

_All the tarsi five-jointed; antennae filiform, or nearly so; mouth-parts

highly developed, the outer lobe of the maxilla nearly always divided

into a two-jointed palpus; supports of the labial palpi developed as

joints of the palpi, and in some cases approximate at their bases.

Abdomen with the exposed segments one more in number at the sides than

along the middle, the number being usually five along the middle, six at

each side._

This extensive series includes the tiger-beetles, ground-beetles, and true

water-beetles; it consists of six families, and forms a natural assemblage.

It is sometimes called Carnivora or Filicornia. The exceptions to the

characters we have mentioned are but few. The supports of the labial palpi

are frequently covered by the mentum, and then the palpi appear

three-jointed; but when the joint-like palpiger is not covered these palps

appear four-jointed. As a rule, approximation of these supports is

indicative of high development. In some of the lower forms the trophi

remain at a lower stage of development than is usual. This is especially

the case with the genus _Amphizoa_, which forms of {201}itself the family

Amphizoidae. The Bombardier-beetles make an exception as regards the

abdominal structure, for in some of them no less than eight segments are

visible, either along the middle line or at the sides of the venter. In

Hydroporides (one of the divisions of Dytiscidae) the front and middle feet

have each only four joints. Many naturalists unite the Gyrinidae with the

Adephaga, and a few also associate with them the Paussidae and Rhysodidae;

but we think it better at present to exclude all these, though we believe

that both Paussidae and Rhysodidae will ultimately be assigned to the

series. The larvae are usually very active, and have a higher development

of the legs than is usual in this Order. Their tarsi possess two claws.

FAM. 4. CICINDELIDAE (_Tiger-beetles_).—_Clypeus extending laterally in

front of the insertion of the antennae. Lower lip with the palpi usually

greatly developed, but with the ligula and paraglossae very much reduced,

often scarcely to be detected. Maxillae with the outer lobe forming a

two-jointed palp,[85] the inner lobe elongate, furnished at the tip with a

hook-like process, which is usually articulated by a joint with the lobe

itself._ The tiger-beetles are very active Insects, running with extreme

speed, and sometimes flying in a similar manner; they are all predaceous,

and amongst the most voracious and fierce of the carnivorous beetles, so

that they well deserve their name. Bates, speaking of the Amazonian

_Megacephala_, says "their powers of running exceed anything I have ever

observed in this style of Insect locomotion; they run in a serpentine

course over the smooth sand, and when closely pursued by the hand they are

apt to turn suddenly back and thus baffle the most practised hand and eye."

He further says that the species he observed (being of diverse colours)

agreed in colour with the general colours of the "locale they inhabit." The

larvae of Cicindelidae live in deep burrows, sinking more or less

vertically into the ground, and in these they take up a peculiar position,

for which their shape is specially adapted; the head and prothorax are

broad, the rest of the body slender, the fifth segment of the abdomen is

furnished on the back with a pair of strong hooks; the ocelli on the sides

of the head are very perfect. Supporting itself at the top of the burrow by

means of these hooks and of its terminal tube, the larva blocks the mouth

of the burrow with its large head and prothorax, and {202}in this position

waits for its prey. This consists of Insects that may alight on the spot or

run over it. When an Insect ventures within reach, the head of the larva is

thrown back with a rapid jerk, the prey is seized by the long sharp

mandibles, dragged to the bottom of the burrow and devoured. The burrows

are often more than a foot deep, and are said to be excavated by the larva

itself, which carries up the earth on the shovel-like upper surface of its

head. The female tiger-beetle is endowed with powerful and elongate

excavating instruments at the termination of the body, and it is probable

that when placing the egg in the earth she facilitates the future

operations of the larva by forming the outlines of the burrow. Extremely

few larvae of Cicindelidae are known, but they all exhibit the type of

structure mentioned above, and apparently have similar habits. Our little

British _Cicindela_, most of which are so active on the wing, agree in

these respects with the African species of _Manticora_, which are entirely

apterous, and are the largest of the Cicindelidae. Péringuey found a

breeding-ground of _M. tuberculata_ near Kimberley; the larvae were living

in the usual Cicindelid manner; but the ground was so hard that he was not

able to investigate the burrows, and there were but few Insects that could

serve as food in the neighbourhood.

[Illustration: Fig. 90—_Cicindela hybrida._ Britain. A, larva (after

Schiödte); B, imago, male.]

The Cicindelidae, although one of the smaller families of Coleoptera, now

number about 1400 species; of these about one-half belong to the great

genus _Cicindela_, to which our four British representatives of the

Cicindelidae are all assigned. There is no general work of much consequence

on this important family, and its classification is not thoroughly

established.[86]

{203}[Illustration: Fig. 91—Mouth-parts of tiger-beetles. A, Profile of

_Pogonostoma_ sp. (Madagascar): _a_, antenna; _b_, labial palp; _c_,

maxillary palp; _d_, palpiform lobe of maxilla; _e_, mandible; _f_, labrum.

B, Section of head of _Manticora maxillosa_ (South Africa): _a_, front of

upper part of head-capsule; _b_, gula; _c_, tentorium; _d_, eye; _e_,

labrum; _f_, left mandible; _g_, maxilla; _h_, maxillary palp; _i_, labial

palp; _k_, support of this palp; _l_, labium.]

Tiger-beetles display considerable variety of structure, especially as

regards the mouth, which exhibits very remarkable developments of the palpi

and labrum (Fig. 91). The tiger-beetles, like most other Insects that

capture living prey, do not consume their victims entire, but subsist

chiefly on the juices they squeeze out of them; the hard and innutritious

parts are rejected after the victim has been thoroughly lacerated and

squeezed; the mouth forms both trap and press; the palpi spread out in

order to facilitate the rapid engulfing of a victim, then close up under it

and help to support it in the mouth; while the labrum above closes the

cavity in the other direction. The mouth itself is a large cavity

communicating very freely with the exterior, but so completely shut off

from the following parts of the alimentary canal that it is difficult to

find the orifice of communication; the labium being much modified to form

the posterior wall. For the capture of the prey, always living but of

various kinds, a mechanism with great holding power and capable of rapid

action is required. The mouth of the terrestrial _Manticora_ (Fig. 91, B),

exhibits great strength; some of the chitinous parts are extremely thick,

the mandibles are enormous, the palpi, however, are comparatively low in

development. In the arboreal genus _Pogonostoma_ the palpary structures

(Fig. 91, A) attain a development scarcely equalled elsewhere in the Insect

world. The great majority of the Cicindelidae are inhabitants of the

warmer, or of the tropical regions of the world, and very little is known

as to their life-histories; they show great diversity in their modes of

hunting their prey. Some are wingless; others are active on the wing; and

of both of these divisions there are forms that are found only on trees or

bushes. Some, it is believed, frequent only the mounds of Termites. The

characteristic feature common {204}to all is great activity and excessive

wariness. The genus _Pogonostoma_, to which we have already alluded, is

confined to Madagascar, where the species are numerous, but are rare in

collections on account of the difficulty of securing them. Raffray informs

us that certain species frequent the trunks of trees, up which they run in

a spiral manner on the least alarm. The only way he could obtain specimens

was by the aid of an assistant; the two approached a tree very quietly from

opposite sides, and when near it, made a rush, and joined hands as high up

the trunk as they could, so as to embrace the tree, when the _Pogonostoma_

fell to the ground and was captured.

[Illustration: Fig. 92—_Leistus spinibarbis._ A, Larva (after Schiödte); B,

imago. Britain.]

FAM. 5. CARABIDAE (_Ground-beetles_).—_Clypeus not extending laterally in

front of the antennae. Maxillae with the outer lobe destitute of an

articulated hook at the tip. Antennae covered (except the basal joints)

with a minute pubescence. Hind legs not very different from the middle

pair, formed for running, as usual in beetles._ This is one of the largest

and most important of the families of Coleoptera, including as it does

12,000 or 13,000 described species. In this country Carabidae are nearly

entirely terrestrial in habits, and are scarcely ever seen on the wing;

many of the species indeed have merely rudimentary wings; in the tropics

there are, however, many arboreal forms that take wing with more or less

alertness. The larvae (Fig. 92, A) are usually elongate in form and run

freely; they may be known by their tarsi ending in two claws, by the

exserted, sharp, calliper-like mandibles, by the body ending in two

processes (sometimes jointed) and a tube of varying length projecting

backwards. The pupae usually have the hind pair of legs so arranged that

the tips of the tarsi project behind, beyond the extremity of the

{205}body. The Carabidae are carnivorous and predaceous both as larvae and

perfect Insects; they attack living Insects, worms, or other small, soft

creatures, but do not disdain dead specimens. Some species of _Carabus_,

found in North Africa where snails abound, are specially formed for

attacking these molluscs, having the head long and slender so that it can

be thrust into the shell of the snail. A few species have been detected

eating growing corn, and even the young seeds of some Umbelliferae; these

belong chiefly to the genera _Harpalus_, _Zabrus_, and _Amara_. Some

species of the abundant genera _Pterostichus_ and _Harpalus_, are said to

be fond of ripe strawberries. The most anomalous forms of Carabidae are the

Pseudomorphides, a sub-family almost peculiar to Australia, the members of

which live under bark, and have but little resemblance to other Carabids

owing to their compact forms and continuous outlines. The genus _Mormolyce_

is one of the wonders of the Insect world on account of the extraordinary

shape of its members; the sides of the elytra form large crinkled

expansions, and the head is unusually elongate. These Insects live on the

underside of fallen trees in the Malay Archipelago and Peninsula; no reason

whatever can be at present assigned for their remarkable shape.

There are a considerable number of blind members of this family: some of

them live in caverns; these belong chiefly to the genus _Anophthalmus_,

species of which have been detected in the caves of the Pyrenees, of

Austria, and of North America. It has been shown that the optic nerves and

lobes, as well as the external organs of vision, are entirely wanting in

some of these cave Carabidae; the tactile setae have, however, a larger

development than usual, and the Insects are as skilful in running as if

they possessed eyes. _Anophthalmus_ is closely related to our British genus

_Trechus_, the species of which are very much given to living in deep

crevices in the earth, or under large stones, and have some of them very

small eyes. In addition to these cavernicolous _Anophthalmus_, other blind

Carabidae have been discovered during recent years in various parts of the

world, where they live under great stones deeply embedded in the earth;

these blind lapidicolous Carabidae are of extremely minute size and of most

sluggish habits; the situations in which they are found suggest that many

successive generations are probably passed under the same stone. Not a

single specimen has ever been found above ground. The minute {206}Carabids

of the genus _Aëpus_, that pass a large part of their lives under stones

below high-water mark (emerging only when the tide uncovers them), on the

borders of the English Channel and elsewhere, are very closely allied to

these blind Insects, and have themselves only very small eyes, which,

moreover, according to Hammond and Miall, are covered in larger part by a

peculiar shield.[87] A few Carabidae, of the genera _Glyptus_ and

_Orthogonius_, are believed to live in the nests of Termites. Savage found

the larva of _G. sculptilis_ in the nests of _Termes bellicosus_; it has

been described by Horn, and is said to bear so great a resemblance to young

queens of the Termites as to have been mistaken for them.[88] Mr. Haviland

found _Rhopalomelus angusticollis_ in Termites' nests in South Africa.

Péringuey states that it emits a very strong and disagreeable odour. It is

probable that it preys on the Termites, and this also is believed to be the

habit of the Ceylonese _Helluodes taprobanae_. Some species of the

Mediterranean genus _Siagona_ stridulate by means of a file on the under

surface of the prothorax, rubbed by a striate area, adapted in form, on the

anterior femora.

A valuable memoir on the classification of this important family is due to

the late Dr. G. H. Horn;[89] he arranges Carabidae in three sub-families;

we think it necessary to add a fourth for _Mormolyce_:

1. Middle coxal cavities enclosed externally by the junction of the meso-

and meta-sternum; neither epimeron nor episternum attaining the

cavity.

Head beneath, with a deep groove on each side near the eye for the

reception of the antennae or a part thereof.

Sub-fam. 3. Pseudomorphides.

Head without antennal grooves. Sub-fam. 2. Harpalides.

2. Middle coxal cavities attained on the outside by the tips of the

episterna and epimera. Sub-fam. 4. Mormolycides.

3. Middle coxal cavities attained on the outside by the tips of the

epimera, but not by those of the episterna.

Sub-fam. 1. Carabides.

These four sub-families are of extremely different extent and nature. The

Harpalides are the dominant forms, and include upwards of 10,000 known

species; while the various tribes into which the sub-family is divided

include, as a rule, each many {207}genera; the Carabides are next in

importance, with upwards of 2000 species, but are divided into a

comparatively large number of tribes, each of which averages a much smaller

number of genera than do the tribes of Harpalides; Pseudomorphides includes

only about 100 species; and Mormolycides consists of the single genus

_Mormolyce_ with three species.

FAM. 6. AMPHIZOIDAE.—_Antennae destitute of pubescence: outer lobe of

maxilla not jointed; metasternum with a short transverse impressed line on

the middle behind. Hind legs slender, not formed for swimming._ This family

is limited to the genus _Amphizoa_; the species of which may be briefly

described as lowly organised Carabidae that lead an aquatic life. The

geographical distribution is highly remarkable, there being but three

species, two of which live in Western North America, the third in Eastern

Tibet. The habits of American _Amphizoa_ are known; they pass a life of

little activity in very cold, rapid streams; they do not swim, but cling to

stones and timber. The larva was recently discovered in Utah by Messrs.

Hubbard and Schwarz:[90] it has the same habits as the perfect Insect, and

in general form resembles the larvae of the genus _Carabus_; but it has no

terminal tube to the body, the abdomen consisting of eight segments and a

pair of short terminal appendages; the spiracles are obsolete, with the

exception of a pair placed near to one another at the termination of the

eighth abdominal segment. As regards the mouth this larva is Carabid, as

regards the abdomen and stigmata Dytiscid of a primitive type.

[Illustration: Fig. 93—_Amphizoa lecontei._ North America. A, Larva; B,

imago.]

{208}[Illustration: Fig. 94—_Pelobius tardus._ Britain. A, Young larva; B,

adult larva; C, imago. (A and B after Schiödte.)]

FAM. 7. PELOBIIDAE.—_Antennae destitute of pubescence: outer lobe of

maxilla jointed, metasternum with a short transverse impressed line on the

middle behind. Hind legs rather slender, formed for swimming, the tarsi

longer than the tibiae._ This family is limited to the one genus _Pelobius_

(_Hygrobia_ of some authors). Like _Amphizoa_, to which it is in several

respects analogous, it has a singular geographical distribution; there are

only four known species, one lives in Britain and the Mediterranean region,

one in Chinese Tibet, two in Australia. _Pelobius_ may be briefly described

as a Carabid adapted to a considerable extent for living in and swimming

about in water; differing thus from _Amphizoa_, which has no special

adaptation for swimming. The larva of _Pelobius_ is remarkable; it breathes

by means of branchial filaments on the under surface of the body, the

spiracles being present, though those of the abdomen are very minute and

the others small. The head is very large, the mandibles are not tube-like,

the food being taken after the manner of the Carabidae; the 8th abdominal

segment ends in three long processes; the small 9th segment is retracted

beneath them. The adult _Pelobius tardus_ is remarkable for its loud

stridulation. The sound is produced by an apparatus described correctly by

Charles Darwin;[91] {209}there is a file on the inside of the wing-cases,

and the Insect turns up the tip of the abdomen and scrapes the file

therewith. The Insects are called squeakers in the Covent Garden market,

where they are sold.

[Illustration: Fig. 95—_Cnemidotus caesus._ England. A, Imago; B, larva,

highly magnified. (After Schiödte.)]

FAM. 8. HALIPLIDAE.—_Antennae bare, ten-jointed; metasternum marked by a

transverse line; posterior coxae prolonged as plates, covering a large part

of the lower surface of the abdomen; the slender, but clubbed, hind femora

move between these plates and the abdomen._ The Haliplidae are aquatic, and

are all small, not exceeding four or five millimetres in length. The

ventral plates are peculiar to the Insects of this family, but their

function is not known. The larvae are remarkable on account of the fleshy

processes disposed on their bodies; but they exhibit considerable variety

in this respect; their mandibles are grooved so that they suck their prey.

In the larva of _Haliplus_, according to Schiödte, there are eight pairs of

abdominal spiracles, but in _Cnemidotus_ (Fig. 95, B), there are no

spiracles, and air is obtained by means of a trachea traversing each of the

long filaments. The Insects of these two genera are so similar in the

imaginal instar that it is well worthy of note that their larvae should be

distinguished by such important characters. Haliplidae is a small family

consisting of three genera, having about 100 species; {210}it is very

widely distributed. We have 13 species in Britain, all the genera being

represented.

[Illustration: Fig. 96.—_Cybister roeseli_ (= _laterimarginalis_ De G.)

Europe. A, Larva (after Schiödte); B, ♂ imago.]

FAM. 9. DYTISCIDAE (_Water-beetles_).—_Antennae bare; hind legs formed for

swimming, not capable of ordinary walking: metasternum without a transverse

line across it; behind closely united with the extremely large coxae. Outer

lobe of maxilla forming a two-jointed palpus._ The Dytiscidae, or true

water-beetles, are of interest because—unlike the aquatic Neuroptera—they

exist in water in both the larval and imaginal instars; nevertheless there

is reason for supposing that they are modified terrestrial Insects: these

reasons are (1) that in their general organisation they are similar to the

Carabidae, and they drown more quickly than the majority of land beetles

do; (2) though the larvae are very different from the larvae of terrestrial

beetles, yet the imaginal instars are much less profoundly changed, and are

capable of existing perfectly well on land, and of taking prolonged flights

through the air; (3) the pupa is, so far as known, always terrestrial. The

larvae and imagos are perfectly at home in the water, except that they must

come to the surface to get air. Some of them are capable, however, when

quiescent, of living for hours together beneath the water, but there

appears to be great diversity in this respect.[92] The hind pair of legs is

the chief means of locomotion. These swimming-legs (Fig. 97) are deserving

of admiration on account of their mechanical perfection; this, however, is

exhibited in various {211}degrees, the legs in the genera _Dytiscus_ and

_Hydroporus_ being but slender, while those of _Cybister_ are so broad and

powerful, that a single stroke propels the Insect for a considerable

distance.

[Illustration: Fig. 97—Hind- or swimming-leg of _Cybister tripunctatus_. A,

The whole leg detached; B, the movable parts in the striking position. _a_,

Coxa; _b_, trochanter; _c_, femur; _d_, tibia; _e_, last joint of tarsus.]

The wing-cases fit perfectly to the body, except at the tip, so as to form

an air-tight space between themselves and the back of the Insect; this

space is utilised as a reservoir for air. When the _Dytiscus_ feels the

necessity for air it rises to the surface and exposes the tip of the body

exactly at the level of the water, separating at the same time the abdomen

from the wing-cases so as to open a broad chink at the spot where the parts

were, during the Insect's submersion, so well held together as to be air-

and water-tight. The terminal two pairs of spiracles are much enlarged, and

by curving the abdomen the beetle brings them into contact with the

atmosphere; respiration is effected by this means as well as by the store

of air carried about under the wing cases. The air that enters the space

between the elytra and body is shut in there when the Insect closes the

chink and again dives beneath the water. The enlargement of the terminal

stigmata in _Dytiscus_ is exceptional, and in forms more highly organised

in other respects, such as _Cybister_, these spiracles remain minute; the

presumption being that in this case respiration is carried on almost

entirely by means of the supply the Insect carries in the space between the

elytra and the base of the abdomen.[93] The structure of the front foot of

the male _Dytiscus_, and of many other water-beetles, is highly remarkable,

the foot being dilated to form a palette or saucer, covered beneath by

sucker-like structures of great delicacy and beauty; by the aid of these

the male is enabled to retain a position on the female for many hours, or

even days, together. Lowne has shown that the {212}suckers communicate with

a sac in the interior of the foot containing fluid, which exudes under

pressure. As the portions of the skeleton of the female on which these

suckers are brought to bear is frequently covered with pores, or minute

pits, it is probable that some correlation between the two organisms is

brought about by these structures. The females in many groups of Dytiscidae

bear on the upper surface of the body a peculiar sculpture of various

kinds, the exact use of which is unknown; in many species there are two

forms of the female, one possessing this peculiar sculpture, the other

nearly, or quite, without it. The larvae of Dytiscidae differ from those of

Carabidae chiefly by the structure of the mouth and of the abdomen. They

are excessively rapacious, and are indeed almost constantly engaged in

sucking the juices of soft and small aquatic animals, by no means excluding

their own kind. The mode of suction is not thoroughly known, but so far as

the details have been ascertained they are correctly described, in the work

on aquatic Insects, by Professor Miall, we have previously referred to; the

mandibles are hollow, with a hole near the tip and another at the base, and

being sharp at the tips are thrust into the body of a victim, and then by

their closure the other parts of the mouth, which are very beautifully

constructed for the purpose, are brought into fitting mechanical positions

for completing the work of emptying the victim. Nagel states that the larva

of _Dytiscus_ injects a digestive fluid into the body of its victim, and

that this fluid rapidly dissolves all the more solid parts of the prey, so

that the rapacious larva can easily absorb all its victim except the

insoluble outer skin. The abdomen consists of only eight segments, and a

pair of terminal processes; the stigmata are all more or less completely

obsolete—according to species—with the exception of the pair on the eighth

segment at the tip of the body; the terminal segments are frequently

fringed with hairs, that serve not only as means of locomotion, but also to

float the pair of active stigmata at the surface when the creature rises to

get air. Although the larvae of Dytiscidae are but little known, yet

considerable diversity has already been found. Those of _Hyphydrus_ and

some species of _Hydroporus_ have the front of the head produced into a

horn, which is touched by the tips of the mandibles.

Dytiscidae are peculiar inasmuch as they appear to flourish {213}best in

the cooler waters of the earth. Lapland is one of the parts of Europe

richest in Dytiscidae, and the profusion of species in the tropics compared

with those of Europe is not nearly so great as it is in the case of most of

the other families of Coleoptera. About 1800 species are at present known,

and we have rather more than 100 species in Britain.[94]

SERIES III. POLYMORPHA.

_Antennae frequently either thicker at the tip (clavicorn) or serrate

along their inner edge (serricorn); but these characters, as well as the

number of joints in the feet and other points, are very variable._

Upwards of fifty families are placed in this series; many of these families

are of very small extent, consisting of only a few species; other families

of the series are much larger, so that altogether about 40,000

species—speaking broadly, about one-fourth of the Coleoptera—are included

in the series. We have already (p. 189) alluded to the fact that it is

formed by certain conventional series, Clavicornia, Serricornia, etc.

united, because it has hitherto proved impossible to define them.

FAM. 10. PAUSSIDAE.—_Antennae of extraordinary form, usually two-jointed,

sometimes six- or ten-jointed. Elytra elongate, but truncate behind,

leaving the pygidium exposed. Tarsi five-jointed._ The Paussidae have

always been recognised as amongst the most remarkable of beetles, although

they are of small size, the largest attaining scarcely half an inch in

length. They are found only in two ways; either in ants' nests, or on the

wing at night. They apparently live exclusively in ants' nests, but migrate

much. Paussidae usually live in the nests of terrestrial ants, but they

have been found in nests of _Cremastogaster_ in the spines of _Acacia

fistulosa_. They have the power of discharging, in an explosive manner, a

volatile caustic fluid from the anus, which is said by Loman to contain

free iodine. Their relations to the ants are at present unexplained, though

much attention has been given to the subject. When observed in the nests

they frequently appear as if asleep, and the ants do not take much notice

of them.

{214}[Illustration: Fig. 98.—_Paussus cephalotes_ ♂. El Hedjaz. (After

Raffray.)]

On other occasions the ants endeavour to drag them into the interior of the

nest, as if desirous of retaining their company: the _Paussus_ then makes

no resistance to its hosts; if, however, it be touched, even very slightly,

by an observer, it immediately bombards: the ants, as may be imagined, do

not approve of this, and run away. Nothing has ever been observed that

would lead to the belief that the ants derive any benefit from the presence

of the Paussi, except that these guests bear on some part of the

body—frequently the great impressions on the pronotum—patches of the

peculiar kind of pubescence that exists in many other kinds of ants'-nest

beetles, and is known in some of them to secrete a substance the ants are

fond of, and that the ants have been seen to lick the beetles. On the other

hand, the Paussi have been observed to eat the eggs and larvae of the ants.

The larva of _Paussus_ is not known,[95] and Raffray doubts whether it

lives in the ants' nests. There are about 200 species of Paussidae known,

Africa, Asia and Australia being their chief countries; one species, _P.

favieri_, is not uncommon in the Iberian peninsula and South France, and a

single species was formerly found in Brazil. The position the family should

occupy has been much discussed; the only forms to which they make any real

approximation are Carabidae, of the group Ozaenides, a group of ground

beetles that also crepitate. Burmeister and others have therefore placed

the Paussidae in the series Adephaga, but we follow Raffray's view (he

being the most recent authority on the family),[96] who concludes that this

is an anomalous group not intimately connected with any other family of

Coleoptera, though having more affinity to Carabidae than to anything else.

The recently discovered genus _Protopaussus_ has eleven joints to the

antennae, and is said to come nearer to Carabidae than the previously known

forms did, and we may anticipate that a more extensive knowledge will show

that the family may find a natural place in the Adephaga. The description

of the abdomen given by Raffray is erroneous; in a specimen of the genus

_Arthropterus_ the writer has dissected, he finds that there {215}are five

ventral segments visible along the middle, six at the sides, as in the

families of Adephaga generally. There is said to be a great difference in

the nervous systems of Carabidae and Paussidae, but so little is known on

this point that we cannot judge whether it is really of importance.

[Illustration: Fig. 99.—A, Larva of _Gyrinus_ (after Schiödte); B, under

side of _Gyrinus_ sp. (after Ganglbauer). 1, Prosternum; 2, anterior coxal

cavity; 3. mesothoracic episternum; 4, mesoepimeron; 5, mesosternum; 6,

metathoracic episternum; 7, middle coxal cavity; 8, metasternum; 9, hind

coxa; 10, ventral segments. [N.B.—The first ventral segment really

consists, at each side, of two segments united; this may be distinctly seen

in many Gyrinidae.]]

FAM. 11. GYRINIDAE (_Whirligig beetles_).—_Antennae very short; four eyes;

middle and hind legs forming short broad paddles; abdomen with six segments

visible along the middle, seven along each side._ These Insects are known

to all from their habit of floating lightly on the surface of water, and

performing graceful complex curves round one another without colliding;

sometimes they may be met with in great congregations. They are admirably

constructed for this mode of life, which is comparatively rare in the

Insect world; the Hydrometridae amongst the bugs, and a small number of

different kinds of Diptera, being the only other Insects that are devoted

to a life on the surface of the waters. Of all these, Gyrinidae are in

their construction the most adapted for such a career. They are able to

dive to escape danger, and they then carry with them a small supply of air,

but do not stay long beneath the surface. Their two hind pairs of legs are

beautifully constructed as paddles, expanding mechanically when moved in

the backward direction, and collapsing into an extremely small space

directly the resistance they meet with is in the other direction. The front

legs of these Insects are articulated to the thorax in a peculiar direction

so that their soles do not look {216}downwards but towards one another;

hence the sensitive adhesive surface used during coupling is placed on the

side of the foot, forming thus a false sole: a remarkable modification

otherwise unknown in Insects. They breathe chiefly by means of the very

large metathoracic spiracles.

The larvae (Fig. 99, A) are purely aquatic, and are highly modified for

this life, being elongate creatures, with sharp, mandibles and nine

abdominal segments, each segment bearing on each side a trachea branchia;

these gills assist to some extent in locomotion. The stigmata are quite

obsolete, but the terminal segment bears four processes, one pair of which

may be looked on as cerci, the other as a pair of gills corresponding with

the pair on each of the preceding segments. The mandibles are not

suctorial, but, according to Meinert, possess an orifice for the discharge

of the secretion of a mandibular gland. Gyrinidae are chiefly carnivorous

in both the larval and imaginal instars. Fully 300 species are known; they

are generally distributed, though wanting in most of the islands of the

world except those of large size. The finest forms are the Brazilian

_Enhydrus_ and the _Porrorhynchus_ of tropical Asia.[97] In Britain we have

nine species, eight of _Gyrinus_, one of _Orectochilus_; the latter form is

rarely seen, as it hides during the day, and performs its rapid gyrations

at night.

The Gyrinidae are one of the most distinct of all the families of

Coleoptera: by some they are associated in the Adephagous series; but they

have little or no affinity with the other members thereof. Without them the

Adephaga form a natural series of evidently allied families, and we

consider it a mistake to force the Gyrinidae therein because an objection

is felt by many taxonomists to the maintenance of isolated families. Surely

if there are in nature some families allied and others isolated, it is

better for us to recognise the fact, though it makes our classifications

look less neat and precise, and increases the difficulty of constructing

"tables."

FAM. 12. HYDROPHILIDAE.—_Tarsi five-jointed, the first joint in many cases

so small as to be scarcely evident: antennae short, of less than eleven

joints, not filiform, but consisting of {217}three parts, a basal part of

one or two elongate joints, an intermediate part of two or more small

joints, and an apical part of larger (or at any rate broader) joints, which

are pubescent, the others being bare. Outer lobe of maxillae usually

complex, but not at all palpiform, maxillary palpi often very long; the

parts of the labium much concealed behind the mentum, the labial palpi very

widely separated. Hind coxae extending the width of the body, short, the

lamina interior small in comparison with the lamina exterior. Abdomen of

five visible segments._ The Hydrophilidae are an extensive family of

beetles, unattractive in colours and appearance, and much neglected by

collectors. A large part of the family live in water, though most of them

have only feeble powers of aquatic locomotion, and the beetles appear

chiefly to devote their attention to economising the stock of air each

individual carries about. The best known forms of the family are the

species of _Hydrophilus_. They are, however, very exceptional in many

respects, and are far more active and predaceous than most of the other

forms. Much has been written about _Hydrophilus piceus_, one of the largest

of British beetles. This Insect breathes in a most peculiar manner: the

spiracles are placed near bands of delicate pubescence, forming tracts that

extend the whole length of the body, and in this particular species cover

most of the under surface of the body; these velvety tracts retain a

coating of air even when the Insect is submerged and moves quickly through

the water. It would appear rather difficult to invent a mechanism to supply

these tracts with fresh air without the Insect leaving the water; but

nevertheless such a mechanism is provided by the antennae of the beetle,

the terminal joints of which form a pubescent scoop, made by some longer

hairs into a funnel sufficiently large to convey a bubble of air. The

Insect therefore rises to the surface, and by means of the antennae, which

it exposes to the air, obtains a supply with which it surrounds a large

part of its body; for, according to Miall, it carries a supply on its back,

under the elytra, as well as on its ventral surface. From the writer's own

observations, made many years ago, he inclines to the opinion that the way

in which the _Hydrophilus_ uses the antennae to obtain air varies somewhat

according to circumstances.