Chapter XIX: Introduction: Habits–classification–structure–chilognatha–chilopoda (13)

From the preceding brief sketch of some Termitidae we may gather the chief points of importance in which they differ from other Insects, viz. (1) the existence in the community of individuals—workers and soldiers—which do not resemble their parents; (2) the limitation of the reproductive power to a single pair, or to a small number of individuals in each community, and the prolongation of the terminal period of life. There are other social Insects besides Termitidae: indeed, the majority of social Insects—ants, bees, and wasps—belong to the Order Hymenoptera, and it is interesting to note that analogous phenomena occur in them, but nevertheless with such great differences that the social life of Termites must be considered as totally distinct from that of the true ants and other social Hymenoptera.

DEVELOPMENT.—Social Insects are very different to others not only in the fact of their living in society, but in respect of peculiarities in the mode of reproduction, and in the variety of habits displayed by members of a community. The greatest confusion has arisen in reference to Termitidae in consequence of the phenomena of their lives having been assumed to be similar to those of Hymenoptera; but the two cases are very different, Hymenoptera passing the early parts of their lives as helpless maggots, and then undergoing a sudden metamorphosis to a totally changed condition of structure, intelligence, and instinct.

The development of what we may look on as the normal form of Termitidae—that is, the winged Insects male and female—is on the whole similar to that we have sketched in Orthoptera; the development in earwigs being perhaps the most similar. The individuals of Termitidae are, however, in the majority of cases if not in all, born without eyes; the wing-rudiments develop from the thoracic terga as shorter or longer lobes according to the degree of maturity; as in the earwigs the number of joints in the antennae increases as development advances. All the young are, when hatched, alike, the differences of caste appearing in the course of the subsequent development; the most important of these differences are those that result in the production of two special classes—only met with in social Insects—viz. worker and soldier. Of these the workers are individuals whose {370}development is arrested, the sexual organs not going on to their full development, while other organs, such as the eyes, also remain undeveloped; the alimentary canal and its adjuncts occupy nearly the whole of the abdominal cavity. The adult worker greatly resembles—except in size—the young. Grassi considers that the worker is not a case of simple arrest of development, but that some deviation accompanies the arrest.

The soldier also suffers an arrest of development in certain respects similar to the worker; but the soldier differs in the important fact that the arrest of the development of certain parts is correlative with an extraordinary development of the head, which ultimately differs greatly from those of either the worker or of the sexual males and females.

SOLDIER.—All the parts of the head of the soldier undergo a greater or less change of form; even the pieces at its base, which connect it by means of the cervical sclerites with the prothorax, are altered. The parts that undergo the greatest modification are the mandibles (Fig. 233, B); these become much enlarged in size and so much changed in form that in a great many species no resemblance to the original shape of these organs can be traced. It is a curious fact that the specific characters are better expressed in these superinduced modifications than they are in any other part of the organisation (except, perhaps, the wings). The soldiers are not alike in any two species of Termitidae so far as we know, and it seems impossible to ascribe the differences that exist between the soldiers of different species of Termitidae to special adaption for the work they have to perform. Such a suggestion is justifiable only in the case of the Nasuti (Fig. 234, 1), where the front of the head is prolonged into a point: a duct opens at the extremity of this point, from which is exuded a fluid that serves as a cement for {371}constructing the nest, and is perhaps also used to disable enemies. Hence the prolongation and form of the head of these Nasuti may be fairly described as adaptation to useful ends. As regards the great variety exhibited by other soldiers—and their variety is much greater than it is in the Nasuti—it seems at present impossible to treat it as being cases of special adaptations for useful purposes. On the whole it would be more correct to say that the soldiers are very dissimilar in spite of their having to perform similar work, than to state that they are dissimilar in conformity with the different tasks they carry on.

The Termite soldier is a phenomenon to which it is difficult to find a parallel among Insects. The soldier in the true ants is usually not definitely distinguished from the worker, but it is possible that in the leaf-cutting ants, the so-called soldier may prove to be more similar in its nature to the Termite soldier. The soldiers of any one species of Termite are apparently {372}extremely similar to one another, and there are no intermediates between them and the other forms, except in the stages of differentiation. But we must recollect that but little is yet known of the full history of any Termite community, and it is possible that soldiers which in the stage of differentiation promise to be unsatisfactory may be killed and eaten,—indeed there is some evidence to this effect. There is too in certain cases some difference—larger or smaller size being the most important—between the soldiers of one species, which may possibly be due to the different stage of development at which their differentiation commenced.

It would at present appear that, notwithstanding the remarkable difference in structure of the soldiers and workers of the white ants, there is not a corresponding difference of instinct. It is true that soldiers do more of certain things than workers do, and less of others, but this appears to be due solely to their possession of such very different structures; and we are repeatedly informed by Grassi that all the individuals in a community take part, so far as they are able, in any work that is going on, and we find also in the works of other writers accounts of soldiers performing acts that one would not have expected from them. The soldiers are not such effective combatants as the workers are. Dudley and Beaumont indeed describe the soldiers as merely looking on while the workers fight.[295] So that we are entitled to conclude that the actions of the soldiers, in so far as they differ from those of the rest of the community, do so because of the different organisation and structures of these individuals. We shall, when speaking of food, point out that the condition of the soldier in relation to food and hunger is probably different from that of the other forms.

VARIOUS FORMS OF A COMMUNITY.—The soldiers and workers are not the only anomalous forms found in Termitid communities; indeed on examining a large nest a variety of forms may be found that is almost bewildering. Tables have been drawn up by Grassi and others showing that as many as fifteen kinds may be found, and most of them may under certain circumstances coexist. Such tables do not represent the results of actual examination in any one case, and they by no means adequately represent the number that, according to the most recent observations of Grassi, may be present; but we give one taken {373}from Grassi, as it conveys some idea of the numerous forms that exist in certain communities. In this table the arrangement, according to A, B, C, D, E, represents successive stages of the development:—

_Forms of Termes lucifugus_. (After Grassi.) _Zool. Anz._ xii. 1889, p. 360.

A 1. Young, undifferentiated larvae.
|
+----------------------+--------------------------+
| | |
B 2. Larvae that will 3. Larvae that will 4. Reserves for royal
not mature the sexual mature the sexual specimens:(only present
organs. organs. when 14, 15, and 11 are
| | wanting, or when 14 and
| | 15 are present in
| | insufficient numbers).
| |
+-----+-----+ +------------+-------------=
| | | | |
C 5. Larvae 6. Larvae 9. Nymphs of 10. Nymphs 11. Reserves for
of soldiers. of workers. the first of the royal pairs (only
| | form. second present when 14,
| | | form. 15, and 4 are
| | | | wanting, or when
| | | | the two latter
D 7. Soldiers. 8. Workers. +----+-----+ | are present in
| | | insufficient
12. Winged 13. Reserve | numbers).
Insects royal pairs? |
| |
E 14. True royal 15. Substitution
couple. royal pairs.

On inspecting this table it will be perceived that the variety of forms is due to three circumstances—(1) the existence of castes that are not present in ordinary Insects; (2) the coexistence of young, of adolescents, and of adults; and (3) the habit the Termites have of tampering with forms in their intermediate stages, the result of which may be the substitution of neoteinic individuals in place of winged forms.

This latter procedure is far from being completely understood, but to it are probably due the various abnormal forms, such as soldiers with rudiments of wings, that have from time to time been discovered in Termite communities, and have given rise to much perplexity.

In connexion with this subject we may call attention to the necessity, when examining Termite nests, of taking cognisance of the fact that more than one species may be present. Bates found different Termites living together in the Amazons Valley, and Mr. Haviland has found as many as five species of Termitidae and three of true ants in a single mound in South Africa. In this latter case observation showed that, though in such close proximity, there was but little further intimacy between the species. There are, however, true inquiline, or guest, Termites, {374}of the genus _Eutermes_, found in various parts of the world living in the nests of other Termitidae.

ORIGIN OF THE FORMS.—The interest attaching to the various forms that exist in Termites, more particularly to the worker and soldier, is evident when we recollect that these never, so far as we know, produce young. In the social Hymenoptera it has been ascertained that the so-called neuters (which in these Insects are always females) can, and occasionally do, produce young, but in the case of the Termites it has never been suggested that the sexual organs of the workers and soldiers, whether male or female, ever become fruitful; moreover, the phenomena of the production of young by the white ants are of such a nature as to render it in the highest degree improbable that either workers or soldiers ever take any direct part in it. Now the soldier is extremely different from the sexual individuals that produce the young, and seeing that its peculiarities are not, in the ordinary sense of the word, hereditary, it must be of great interest to ascertain how they arise.

Before stating the little information we possess on this subject, it is necessary to reiterate what we have already said to the effect that the soldiers and workers are not special to either sex, and that all the young are born alike. It would be very natural to interpret the phenomena by supposing the workers to be females arrested in their development—as is the case in social Hymenoptera—and by supposing the soldiers to be males with arrested and diverted development.

The observations already made show that this is not the case. It has been thoroughly well ascertained by Lespès and Fritz Müller that in various species of _Calotermes_ the soldiers are both males and females. Lespès and Grassi have shown that the workers of _Termes lucifugus_ are of male and female sex, and that this is also true of the soldiers. Although the view of the duality of the sexes of these forms was received at first with incredulity, it appears to be beyond doubt correct. Grassi adds that in all the individuals of the workers and soldiers of _Termes lucifugus_ the sexual organs, either male or female, are present, and that they are in the same stage of development whatever the age of the individual. This statement of Grassi's is of importance because it seems to render improbable the view that the difference of form of the soldier and worker arises from the arrest of the {375}development of their sexual organs at different periods. The fact that sex has nothing whatever to do with the determination of the form of workers and soldiers may be considered to be well established.

The statement that the young are all born alike is much more difficult to substantiate. Bates said that the various forms could be detected in the new-born. His statement was made, however, merely from inspection of the nests of species about which nothing was previously known, and as it is then very difficult to decide that a specimen is newly hatched, it is probable that all he meant was that the distinction of workers, soldiers, and sexual forms existed in very small individuals—a statement that is no doubt correct. Other observers agree that the young are in appearance all alike when hatched, and Grassi reiterates his statement to this effect. Hence it would appear that the difference of form we are discussing arises from some treatment subsequent to hatching. It may be suggested, notwithstanding the fact that the young are apparently alike when hatched, that they are not really so, but that there are recondite differences which are in the course of development rendered conspicuous. This conclusion cannot at present be said with certainty to be out of the question, but it is rendered highly improbable by the fact ascertained by Grassi that a specimen that is already far advanced on the road to being an ordinary winged individual can be diverted from its evident destination and made into a soldier, the wings that were partially developed in such a case being afterwards more or less completely absorbed. This, as well as other facts observed by Grassi, render it probable that the young are truly, as well as apparently, born in a state undifferentiated except as regards sex. Fig. 230 (p. 363) is designed to illustrate Grassi's view as to this modification; the individual A is already far advanced in the direction of the winged form C, but can nevertheless be diverted by the Termites to form the adult soldier B.

According to the facts we have stated, neither heredity nor sex nor arrest of development are the causes of the distinctions between worker and soldier, though some arrest of development is common to both; we are therefore obliged to attribute the distinction between them to other influences. Grassi has no hesitation in attributing the anatomical distinctions that arise between the soldiers, workers, and winged forms to alimentation. {376}Food, or the mode of feeding, or both combined, are, according to the Italian naturalist, the source of all the distinctions, except those of sex, that we see in the forms of any one species of Termite.

FEEDING.—Such knowledge as we possess of the food-habits of Termitidae is chiefly due to Grassi; it is of the very greatest importance, as giving a clue to much that was previously obscure in the Natural History of these extraordinary creatures.

In the abodes of the Termites, notwithstanding the enormous numbers of individuals, cleanliness prevails; the mode by which it is attained appears to be that of eating all refuse matter. Hence the alimentary canal in Termitidae contains material of various conditions of nutritiveness. These Insects eat their cast skins and the dead bodies of individuals of the community; even the material that has passed through the alimentary canal is eaten again, until, as we may presume, it has no further nutritive power. The matter is then used for the construction of their habitations or galleries, or is carried to some unfrequented part of the nest, or is voided by the workers outside of the nests; the pellets of frass, _i.e._ alimentary rejectamenta, formed by the workers frequently betraying their presence in buildings when none of the Insects themselves are to be seen. The aliments of _Calotermes flavicollis_ are stated by Grassi and Sandias to be as follows: (1) wood; (2) material passed from the posterior part of the alimentary canal or regurgitated from the anterior part; (3) the matter shed during the moults; (4) the bodies of other individuals; (5) the secretion of their own salivary glands or that of their fellows; (6) water. Of these the favourite food is the matter passed from the posterior part of the alimentary canal. We will speak of this as proctodaeal food. When a _Calotermes_ wishes food it strokes the posterior part of another individual with the antennae and palpi, and the creature thus solicited yields, if it can, some proctodaeal food, which is then devoured. Yielding the proctodaeal food is apparently a reflex action, as it can be induced by friction and slight pressure of the abdomen with a small brush. The material yielded by the anterior part of the alimentary canal may be called stomodaeal product. It makes its appearance in the mouth in the form of a microscopic globule that goes on increasing in size till about one millimetre in diameter, when it is {377}either used for building or as food for another individual. The mode of eating the ecdysial products has also been described by Grassi and Sandias. When an individual is sick or disabled it is frequently eaten alive. It would appear that the soldiers are great agents in this latter event, and it should be noticed that owing to their great heads and mandibles they can obtain food by other means only with difficulty. Since they are scarcely able to gnaw wood, or to obtain the proctodaeal and stomodaeal foods, their condition may be considered to be that of permanent hunger, only to be allayed by carnivorous proceedings. When thrown into a condition of excitement the soldiers sometimes exhibit a sort of Calotermiticidal mania, destroying with a few strokes five or six of their fellows. It is, however, only proper to say that these strokes are made at random, the creature having no eyes. The carnivorous propensities of _Calotermes_ are apparently limited to cannibalism, as they slaughter other white ants (_Termes lucifugus_) but never eat them.

The salivary food is white and of alkaline nature; when excreted it makes its appearance on the upper lip. It is used either by other individuals or by the specimen that produced it; in the latter case it is transferred to the lower lip and swallowed by several visible efforts of deglutition. The aliments we have mentioned are made use of to a greater or less extent by all the individuals except the very young; these are nourished only by saliva: they commence taking proctodaeal and stomodaeal food before they can eat triturated wood.

ROYAL PAIRS.—The restriction of the reproductive powers of a community to a single pair (or to a very restricted number of individuals) occurs in all the forms of social Insects, and in all of them it is concomitant with a prolongation of the reproductive period far exceeding what is natural in Insects. We are not in a position at present to say to what extent the lives of the fertile females of Termitidae are prolonged, there being great difficulties in the way of observing these Insects for long periods owing to their mode of life; living, as they do, concealed from view, light and disturbance appear to be prejudicial to them. We have every reason to believe, however, that the prolongation extends as a rule over several years, and that it is much greater than that of the other individuals of the community, although the lives of even these latter are longer than is usual in Insects; but this {378}point is not yet satisfactorily ascertained. As regards the males there is reason to think that considerable variety as to longevity prevails. But the belief is that the royal males of Termitidae also form an exception to other Insects in the prolongation of the terminal periods of their lives. In Hymenoptera, male individuals are profusely produced, but their lives are short, and their sole duty is the continuation of the species by a single act. We have seen that Grassi is of opinion that a similar condition of affairs exists at present with _Termes lucifugus_ in Sicily, but with this exception it has always been considered that the life of the king Termite is, roughly speaking, contemporaneous with that of the queen; it is said that in certain species the king increases in bulk, though not to an extent that can be at all compared with the queen.

It must be admitted that the duration of life of the king has not been sufficiently established, for the coexistence of a king with a queen in the royal cell is not inconsistent with the life of the king being short, and with his replacement by another. Much that is imaginary exists in the literature respecting Termites, and it is possible that the life of the king may prove to be not so prolonged as has been assumed.

Returning to the subject of the limitation of the reproduction of the community to a single pair, we may remark that _a priori_ one would suppose such a limitation to be excessively unfavourable to the continuation of the species; and as it nevertheless is the fact that this feature is almost, if not quite, without exception {379}in Insect societies, we may conclude that it is for some reason absolutely essential to Insect social life. It is true that there are in Termitidae certain partial exceptions, and these are so interesting that we may briefly note them. When a royal cell is opened it usually contains but a single female and male, and when a community in which royal cells are not used is inspected it is usually found that here also there are present only a single fertile female and a single king. Occasionally, however, it happens that numerous females are present, and it has been noticed that in such cases they are not fully matured females, but are imperfect, the condition of the wings and the form of the anterior parts of the body being that of adolescent, not adult Insects. It will be recollected that the activity of a community of Termites centres round the great fertility of the female; without her the whole community is, as Grassi graphically puts it, orphaned; and the observations of the Italian naturalist make it clear that these imperfect royalties are substitution queens, derived from specimens that have not undergone the natural development, but have been brought into use to meet the calamity of orphanage of the community. The Termites apparently have the power of either checking or stimulating the reproductive organs apart from other organs of the body, and they appear to keep a certain number of individuals in such a condition that in case of anything going wrong with the queen, the reserves may be brought as soon as possible into a state of reproductive activity. The individuals that are in such a condition that they can become pseudo-royalties are called complementary or reserve royalties, and when actually brought into use they become substitution royalties. It is not at present quite clear why the substitution royalties should be in such excess of numbers as we have stated they were in the case we have figured (Fig. 236), but it may be due to the fact that when the power of the community is at a certain capacity for supporting young a single substitution royalty would not supply the requisite producing power, and consequently the community adopts a greater number of the substitution forms. Termites are utterly regardless of the individual lives of the members of the community, and when the reproductive powers of the company of substitution royalties become too great, then their number is reduced by the effective method of killing and eating them.

According to Grassi's observations, the communities of _Termes {380}lucifugus_ are now kept up in Sicily almost entirely by substitution royalties; the inference being that the age of each community has gone beyond the capacity for life of any single royal queen.

The substitution royalties are, as we have said, called neoteinic (νεος, youthful, τείνω, to belong to), because, though they carry on the functions of adult Insects, they retain the juvenile condition in certain respects, and ultimately die without having completed the normal development. The phenomenon is not quite peculiar to Insects, but occurs in some other animals having a well-marked metamorphosis, notably in the Mexican Axolotl.[296]

A point of great importance in connexion with the neoteinic royalties is that they are not obtained from the instar immediately preceding the adult state, but are made from Insects in an earlier stage of development. The condition immediately preceding the adult state is that of a nymph with long wing-pads; such specimens are not made into neoteinic royalties, but nymphs of an earlier stage, or even larvae, are preferred. It is apparently by an interference with one of these earlier stages of development that the "nymphs of the second form," which have for long been an enigma to zoologists, are produced.

POST-METAMORPHIC GROWTH.—The increase of the fertility of the royal female is accompanied by remarkable phenomena of growth. Post-metamorphic growth is a phenomenon almost unknown in Insect life, except in these Termitidae; distension not infrequently occurs to a certain extent in other Insects, and {381}is usually due to the growth of eggs inside the body, or to the repletion of other parts. But in Termitidae there exists post-metamorphic growth of an extensive and complex nature; this growth does not affect the sclerites (_i.e._ the hard chitinous parts of the exo-skeleton), which remain of the size they were when the post-metamorphic growth commenced, and are consequently mere islands in the distended abdomen (Fig. 236, B, C). The growth is chiefly due to a great increase in number and size of the egg-tubes, but there is believed to be a correlative increase of various other parts of the abdominal as distinguished from the anterior regions of the body. A sketch of the distinctions existing between a female of a species at the time of completion of the metamorphosis and at the period of maximum fertility does not appear to have been yet made.

NEW COMMUNITIES.—The progress of knowledge in respect of Termitidae is bringing to light a quite unexpected diversity of habits and constitution. Hence it is premature to generalise on important matters, but we may refer to certain points that have been ascertained in connexion with the formation of new communities. The duration of particular communities and the modes in which new ones are founded are still very obscure. It was formerly considered that swarming took place in order to increase the number of communities, and likewise for promoting crossing between the individuals of different communities. Grassi, however, finds as the result of his prolonged observations on _Termes lucifugus_ that the swarms have no further result than that the individuals composing them are eaten up. And Fritz Müller states[297] that in the case of the great majority of forms known to him the founding of a colony by means of a pair from a swarm would be just about as practicable as to establish a new colony of human beings by placing a couple of newly-born babes on an uninhabited island. It was also thought that pairs, after swarming, re-entered the nests and became royal couples. It does not, however, appear that any one is able to produce evidence of such an occurrence. The account given by Smeathman of the election of a royal couple of _Termes bellicosus_ is imperfect, as, indeed, has already been pointed out by Hagen. It suggests, however, that a winged pair after leaving the nest do again enter it to become king {382}and queen. The huge edifices of this species described by Smeathman are clearly the result of many years of labour, and at present substitution royalties are not known to occur in them, so that it is not improbable Smeathman may prove to be correct even on this point, and that in the case of some species mature individuals may re-enter the nest after swarming and may become royal couples. On the whole, however, it appears probable that communities of long standing are kept up by the substitution royalty system, and that new communities when established are usually founded by a pair from a swarm, which at first are not in that completely helpless condition to which they come when they afterwards reach the state of so-called royalty. Grassi's observations as to the sources of food remove in fact one of the difficulties that existed previously in regard to the founding of new colonies, for we now know that a couple may possibly bear with them a sufficient supply of proctodaeal and stomodaeal aliment to last them till workers are hatched to feed them, and till soldiers are developed and the community gradually assumes a complex condition. Professor Perez has recently obtained[298] the early stages of a community from a winged pair after they had been placed in captivity, unattended by workers. Müller's observation, previously quoted, is no doubt correct in relation to the complete helplessness of royal pairs after they have been such for some time; but that helplessness is itself only gradually acquired by the royal pair, who at first are able to shift for themselves, and produce a few workers without any assistance.

ANOMALOUS FORMS.—Müller has described a _Calotermes_ under the name of _C. rugosus_, which is interesting on account of the peculiar form of the young larva, and of the changes by which it subsequently becomes similar in form to other species of the genus. We represent the development of this larva in Fig. 237. We may call attention to the fact that this figure illustrates the large size of the paunch, which is so extraordinary in some of the states of the Termitidae.

It will be recollected that the genus _Calotermes_ is destitute of workers. There is another genus, _Anoplotermes_, in which the reverse condition prevails, and the soldier is absent; this is the only case yet known in which such a state of affairs exists. {383}The species is called _A. pacificus_ by Fritz Müller; it differs from other Termitidae in possessing a proventriculus destitute of triturating ridges. The nests of this species are utilised by a little _Eutermes_ (_E. inquilinus_ Müller) for its own advantage; whether by first destroying the _Anoplotermes_ or whether by merely taking possession of the nests abandoned by their owners is not known. It is a most remarkable fact that the _Eutermes_ resembles the _Anoplotermes_ so extremely that the two can scarcely be distinguished, though anatomically they are quite different. The resemblance is indeed so great that it deceived Von Jhering into supposing that the two genera were alternate generations of a single species, one generation possessing soldiers, the other being without them. Subsequently, by anatomical investigation, he recognised[299] the error into which he had fallen—an error that, under such peculiar circumstances, was quite pardonable.

Hagen has suggested[300] that _Hodotermes japonicus_ never produces winged forms. Very little, however, is actually known as to this species.

MARCHING AND HARVESTING TERMITES.—Smeathman alluded to a remarkable _Termes_ seen by him in Africa, giving it the name of _T. viarum_. Nothing further is known of this Insect, which, according to Smeathman's account, may possibly be the most remarkable of the family. _T. viarum_ is said to be larger than _T. bellicosus_, and was discovered issuing in large numbers from a hole in the ground and marching in columns consisting of workers directed by soldiers of enormous size, some of whom {384}climbed up plants and gave audible signals to the army, which immediately responded with a hissing noise and by increasing their pace with the utmost hurry; they continued marching by the spot where Smeathman observed them for upwards of an hour. He was not able to find their nests, and no specimens have been preserved; both soldiers and workers possessed eyes. Marching in this way by daylight is contrary to the nature of ordinary Termites, and some doubt has existed as to the correctness of Smeathman's observation, which has in fact remained for upwards of a century without confirmation.

Mr. G. D. Haviland has, however, this year discovered in Natal a Termite which shows that there are species in Africa of the kind described by Smeathman, the workers and soldiers being possessed of facetted eyes. Mr. Haviland states that the workers of this species issue from holes in the ground during the heat of the day and cut grass both dead and green. They carry it, in lengths of about two inches, to the mouths of the holes, often leaving it there and going at once to fetch more. Under acacia bushes they carry acacia leaflets as well as grass. In the middle of the day more grass accumulates at the entrance to the holes than can be taken in, but as the heat of the day diminishes the workers cease to forage and take in the accumulation. When the grass is all in they sometimes close the mouth of the hole with moistened pellets of earth brought in their mouths. The soldiers remain in the holes; when disturbed they jerk themselves like soldiers of other species to frighten away the intruder; when they bite, their grip is very tenacious. The holes are about ⅓ of an inch in diameter, and there are usually several of them a few yards apart; around each {385}of them is a patch over which the grass has been cut quite short. Mr. Haviland followed these holes by digging for a distance of 20 feet and to a depth of 5½ feet; they remain uniform in size except that near the entrance there may be one or two chambers in which the grass is temporarily stored, but these do not hold more than would be collected in an hour or two. As the burrow descends it is occasionally joined by another, and at the point of junction there is usually a considerable widening. Sometimes they run straight for 6 or 7 feet, sometimes they curve abruptly, sometimes they are nearly horizontal, but near the mouth may be almost vertical in direction. These Termites are very local, but the specimens are numerous when found. Mr. Haviland dug for these Insects at two places on the Tugela river, one of them being at Colenso. It is much to be regretted that he was unable to reach the nest. We figure a soldier selected from specimens sent by Mr. Haviland to the Cambridge University Museum. This Insect is apparently much smaller than Smeathman's _T. viarum_. Other species of Termitidae have been described[301] as forming underground tunnels in Africa, but none of the species have yet been satisfactorily identified.

It was stated by Smeathman that some species of Termites had chambers in their habitations in which grew a kind of fungus used by the Insects for food; Mr. Haviland is able to confirm Smeathman in this particular; he having found fungus-chambers in the nests of more than one species both in Singapore and South Africa (Fig. 240).

HABITATIONS.—In nothing do Termites differ more than in the habitations they form. Sometimes, as we have mentioned in the case of _Calotermes_, there is no real structure formed; only a few barriers being erected in burrows or natural hollows in wood. In other cases very extensive structures are formed, so that the work of the Termites becomes a conspicuous feature in the landscape. This is of course only the case in regions that are not much interfered with by man; the great dwellings spoken of by Smeathman and others soon disappear from the neighbourhood of settlements, but in parts of Africa and in Australia large dwellings are still formed by these creatures. In the latter part of the world there exists a very remarkable one, formed by an {386}undetermined species called by the officers and crew of her Majesty's ship _Penguin_ the "compass ant." The outline of one of the structures formed by this Termite we represent in Fig. 239. Mr. J. J. Walker, to whom we are indebted for the sketch from which this figure is taken, has also favoured us with the following extract from his diary, of date 4th August 1890: "The most interesting feature in the scenery (about forty miles inland from Port Darwin) was the constant succession of huge mounds raised by the Termites, of which I had seen some comparatively small examples in my rambles near Port Darwin; but these exceeded in dimensions all I had ever seen. The most frequent as well as the largest kind was usually of a reddish or ferruginous colour outside, and generally almost cylindrical in shape with obtusely-pointed top, but nearly always more or less weather-worn, with great irregular buttresses and deep ruts down the sides; many of them look like ruined towers in miniature. Their usual height was from 8 to 10 feet, but many were much higher, and some attained an (estimated) elevation of at least 20 feet. Another kind, seen only in one or two places along the line, was of a much more singular character; they averaged only 4 to 5 feet high, were built of a dark-gray mud, and in shape were like thin flat wedges set upright (see Fig. 239), reminding one of tombstones in a churchyard. But the most remarkable feature about these mounds was that they had all the same orientation, viz. with the long faces of the wedge pointing nearly north and south. Why this is so I am quite at a loss to imagine, and I much regret that I had no opportunity of closely examining these most singular structures. A third kind of mound, usually not exceeding 2 feet in height, was of a simple, acute, conical figure, and generally of a gray colour somewhat paler than the last."

The material used for the construction of the dwellings is either earth, wood, or the excrement of the Termites. The huge edifices mentioned by Smeathman are composed of earth cemented {387}together so as to look like stone or brick, and the buildings appear to be almost as strong as if they were actually constructed with these materials. In many cases the substance used is comminuted wood that has passed one or more times through the alimentary canal of the Insects, and may therefore be called excrement. Whether the stone-like material is made from earth that has passed through the alimentary canal or from grains gathered for the purpose has not been well ascertained. In any case the material is cemented together by means of the secretions of glands. Dudley and Beaumont have described the process of construction, in a species observed by them, saying that earth is brought and placed in position by the mandibles, and cemented by liquid from the abdomen.[302] Von Jhering says[303] that some species form the exterior walls of their dwellings of stone-like material, but make use of woody matter for the construction of the interior. Smeathman has described the nest of _Termes bellicosus_. The whole of the very strong external wall consists of clay-like material, cemented by the secretions of the Termites to a very firm consistence. The royal cell is built of the same material as the framework of the nest; whilst the nurseries in which the young are chiefly found are built of woody material, and are always covered with a kind of mould—the mycelium of a fungus—and plentifully sprinkled with small white bodies, which, under the microscope, are found to be filled with a number of oblong, spore-like cells.

These nurseries rest on the clay-like framework of the nest, but are not attached thereto; they in no way support it, or one another, indeed they have the appearance of being constantly added to on their upper margins and constantly eaten away on their under parts. Fig. 240 represents the appearance of the upper boundary of a nursery taken from a nest of _Termes angustatus_. The small white bodies, mentioned above, have disappeared: the mycelium of the fungus, though not shown in the {388}figure, is still visible on the specimen from which it was drawn, and gives rise to a whitish, glaucous appearance.

In various parts of the world nests formed on trees by Termites are to be seen; these tree nests are, it would appear, in some cases only parts of a community, and are connected with the main body by galleries. In other cases nests are formed in various positions of advantage; Messrs. Hubbard and Hagen have given us an account[304] of some of these—probably the work of _Eutermes ripperti_—as seen in Jamaica. They describe the nests as spherical or conical masses, looking externally as if composed of loamy earth; they are placed on trees, fences, or walls; they vary in size from that of a man's fist to that of a hogshead; they appear to be composed of finely comminuted wood fastened together by saliva. These nests are formed on the same principle as those of the wasps that make nests hanging to trees and bushes, as they consist of an external protecting envelope covering a comb-like mass in the interior. At the bottom of the nest there is a covered gallery leading to the earth, where the main nest appears to be situate; galleries also are constructed so as to lead to the tops of trees and other places, in such a manner that the Termite can still keep up its peculiarity of working and travelling in tunnels and yet roam over a large area; the activity of these Termites continues day and night. In each nest there is a queen, who lays eggs that are removed by the worker Termites to the bottom of the nest. The young are fed on a prepared food, consisting apparently of comminuted vegetable matter, of which considerable masses are laid in store. Some of the nests are rich in containing many pounds' weight of this material, while others are apparently quite destitute of it. There is a soldier form and at least two kinds of workers. Some species of true ant frequently shares the nest of these white ants, but on what terms the two kinds of Insects live together is not stated.

TERMITE RAVAGES.—In countries whose climate is favourable to their constitutions certain kinds of Termites become of great importance to our own species. Owing to their taste for woody matter and to their habit of working in concealment, it is no uncommon thing for it to be discovered that Termites have obtained access to a building and have practically destroyed the wooden materials used in its construction; all the interior of the {389}wood being eaten away and only a thin outer shell left intact. A Termite, _T. tenuis_, was introduced—in what manner is not certainly known[305]—to the Island of St. Helena, and committed such extensive ravages there that Jamestown, the capital, was practically destroyed and new buildings had to be erected. Other such cases are on record. Destructive species can sometimes be destroyed by placing in the nests a portion of arsenicated food. This is eaten by some individuals, who perish in consequence; and their dead bodies being consumed by their comrades, the colony becomes checked if not exterminated.

The number of described species of Termitidae does not much exceed 100, but this is certainly only a small portion of those existing, the total of which may probably reach 1000 species.

Termitidae are classed by some naturalists with the Orthoptera, and they have a great deal in common with some of the cursorial division of that Order, more particularly Forficulidae and Blattidae; but they differ from Orthoptera in the nature and form of the wings. They are also classed by some, with a few other forms, as a separate Order of Pseudo-Neuroptera called Corrodentia, but this is not a very satisfactory course, as the Termitidae do not agree closely with the forms associated with them, while the aggregate so formed is far from being very distinct from other forms of Neuroptera. On the whole the best plan appears to be to treat the Termitidae as forming a distinct family of the Order Neuroptera, or to make it a distinct Order, as proposed by Grassi. Packard now associates Termites in an Order with the biting-lice, and calls it Platyptera.

FOSSIL TERMITES.—Termitidae were very abundant in Tertiary times, and the genera appear to have been then much the same as at present. In Mesozoic strata the remains of true Termitidae apparently exist in the Lias in Europe, but farther back than this the family has not been satisfactorily traced. It was formerly supposed that Termitidae existed in the Carboniferous strata, but this appears to be very doubtful; and the fossil remains of that epoch, which were presumed to be those of Termites, are now referred by Scudder and others to the Neuropteroid division of the Order Palaeodictyoptera, an Order which is formed entirely of Palaeozoic fossil remains.

{390}CHAPTER XVII

NEUROPTERA _CONTINUED_—PSOCIDAE (BOOK-LICE AND DEATH-WATCHES)—THE FIRST FAMILY OF AMPHIBIOUS NEUROPTERA (PERLIDAE, STONE-FLIES).

FAM. IV. PSOCIDAE—BOOK-LICE, DEATH-WATCHES.

_Minute Insects with slender, thread-like, or hair-like antennae; four
delicate membranous wings, the front pair of which are the larger; their
neuration is not abundant and is irregular, so that the cells are also
irregularly arranged; the transverse nervules are only one or two in
number.[306] Prothorax very small, in the winged forms quite concealed
between the head and the large mesothorax; this latter closely connected
with, or fused with, the metathorax. Species quite wingless, or with
wings unfitted for flight, exist; in them the prothorax is not so
extremely small, while the mesothorax is smaller than in the winged
forms. Tarsi of two or three segments. Metamorphosis slight, marked
chiefly by the development of wings and ocelli._

The Psocidae are without exception small and soft-bodied Insects, and are only known to those who are not entomologists by the wingless forms that run about in uninhabited or quiet apartments, and are called dust-lice or book-lice. They are perhaps more similar to Termitidae than to any other Insects, but the two families differ much in the structure of their wings, and are totally dissimilar in the nature of their lives.

{391}

The antennae consist of eleven to twenty-five joints, or even more, about thirteen being the usual number; the basal two are thicker than the others, and are destitute of setae or pubescence such as the others possess. The maxillae and labium are remarkable. The former possesses a peculiar hard pick or elongate rod; this is considered by many naturalists to be the inner lobe, but Burgess thinks it more probably an independent organ,[307] as it has no articulation of any kind with the outer lobe. The latter is remarkably thick and fleshy; the palpus is 5-jointed. Other authorities consider the pick to be certainly the inner lobe; if it be not, the latter is quite wanting. Hagen agrees with Burgess in stating that the pick slides in the outer lobe as in a sheath. The labium has a large mentum and a ligula divided anteriorly into two lobes; at each outer angle in front there is a globular projection, which is doubtless the labial palpus; reposing on the labium there is a large free lingua. The labrum is large, attached to a distinct clypeus, behind which there is a remarkable post-clypeus, which is usually prominent as if inflated; to its inner face are attached several muscles which converge to be inserted on a plate placed below the anterior part of the oesophagus, and called by Burgess the {392}oesophageal bone; under or within the lingua there is a pair of lingual glands. Judging from Grosse's study of the mouth of Mallophaga, we may conclude that the oesophageal bone will prove to be a sclerite of the hypopharynx. The eyes of the winged forms are frequently remarkably convex, and there are also three ocelli, triangularly placed on the vertex. The head is free and very mobile. The coxae are rather small, exserted, contiguous; the sterna small. The abdomen has usually ten segments, though sometimes only nine can be detected.

The thorax in Psocidae usually looks as if it consisted of only two segments. This is due to two opposite conditions: (1) that in the winged forms the prothorax is reduced to a plate concealed in the fissure between the head and the mesothorax bearing the first pair of wings; (2) that in the wingless forms (Fig. 247), though the prothorax is distinct, the meso- and metathorax are fused into one segment.

The internal anatomy is only very incompletely known. Nitzsch[308] has, however, described the alimentary canal and the reproductive organs of _Clothilla pulsatoria_. The former is remarkably simple: no proventriculus or crop was found; the stomach is very elongate, and consists of a sac-like anterior portion and an elongate, tubular posterior part. There are four Malpighian tubes. The posterior part of the canal is remarkably short, the small intestine being scarcely as long as the rectum. The ovaries (Fig. 244, B) consist of five egg-tubes on each side; connected with the oviduct there is a peculiar accessory gland consisting of a sac containing other small sacs each {393}with an elongate efferent duct; the number of the secondary sacs varies from one to four according to the individual. The testis (Fig. 244, A, _b_) is a simple capsule; connected with the base of the ejaculatory duct there is a pair of elongate accessory glands or vesiculae seminales.

The life-history has never been satisfactorily sketched. The young greatly resemble the old, but have no ocelli or wings, and sometimes the tarsi are of two joints, while in the adult they have three. The antennae have also in these cases a less number of joints in the young stage. The food is animal or vegetable refuse substances; many live on fungoid matter of various kinds, mouldy chaff being, it is said, a favourite pabulum; the mould on palings is a source of food to many; others live on the rust-fungi of leaves, and many frequent the bark of trees. They are able to spin webs, probably by the aid of the lingual glands; the eggs are deposited, in some cases, on leaves and covered with a web. Hagen says that a peculiar organ, possibly a gland—he calls it a hose[309]—exists at the base of the tarsal claws. In our climate most of the species pass the winter in the egg-state. There may be two generations in a year, perhaps more.

The nomenclature of the wing-veins of Psocidae has given rise to much discussion.[310] The system shown in the accompanying figure is probably the most convenient; the subcostal vein (2) is always obscure, and sometimes can only be detected by very minute examination. Some interesting information as to the minute structure and mode of formation of the wings and their nervures has been given by Hagen.[311]

In the young the wings first appear as buds, or outgrowths of the sides of the meso- and meta-thorax; afterwards the prothorax decreases, while the other two thoracic segments and the wing-rudiments attached to them increase. The wings from their very origin appear to be different from those of the Orthoptera, and the changes that take place in the thoracic {394}segments in the course of the development, differ from those that occur in Orthoptera.

There are several peculiarities connected with the wings. Frequently they exist, though of no use for flight; some Psocidae that have perfectly-formed wings are so reluctant to use them that, M‘Lachlan says, they will allow themselves to be crushed without seeking to escape by flight. At certain periods, however, some Psocidae float on the wing in considerable numbers, especially in a moist still atmosphere, and then drift about like the winged Aphididae, which are frequently found with them. There is evidence that individuals, or generations, of some of the winged species occur with only rudimentary wings; although this has been denied by Kolbe, there can be no doubt about it. The form figured above (Fig. 246) was described by Bertkau[312] as a distinct genus, but was afterwards recognised by him[313] to be a short-winged form of _Mesopsocus unipunctatus_. It is probable that the adult female of this species has the wings always micropterous, while the male has these organs of the full size. In other species the condition of the rudimentary wings seems to be quite constant. The facts concerning the wings of Psocidae are so peculiar that Kolbe came to the conclusion that the organs exist not because they are of use for flight, so much as because it is the nature of an Insect to develop wings.[314]

Some of the species of Psocidae have never any trace of wings. These apterous forms are mostly included in the division Atropinae, and are usually very minute; it has been again and again erroneously stated that they are the young state of winged forms. Hagen kept a large colony of _Atropos divinatoria_ for some years in confinement, so that he saw numerous generations as well as many specimens. He found the apterous condition quite constant.