1911 Encyclopædia Britannica/Termite
TERMITE, the name applied to a group of insects with four wings which are developed outside the body (a large proportion of the individuals become adult, however, without wings appearing at all). The wings are of nearly one size, of long, narrow form, of paper-like consistence, and in repose are placed flat on the back of the insect so that only one wing shows. After a short time the wings are shed, and only small stumps remain as evidence of the individual being a winged form. The mouth has strong mandibles. Formerly termites were classed as a part of the order Neuroptera, but more recently they have been separated by certain zoologists from the true Neuroptera, and associated with some other forms as an order Corrodentia. By Packard they have been associated with Mallophaga, and called Platyptera. They now constitute with the Embiidæ—a small and obscure family—the order Isoptera, of which about 300 species are known. Termites are more widely known as white ants, but as they are extremely different from true ants, and as they are rarely white, this designation is very deceptive, and should be abandoned.
Termites are found only in warm climates, where they are sometimes very destructive. They are vegetarian, but occasionally eat, or destroy, dry animal matter. The basis of their alimentary regimen is woody matter. Some of them make use of fungi growing in their abodes as food; some cut and store grass; others prepare a peculiar kind of food, which is stored in a tough, dry form, so that it has to be moistened before it can be eaten. Termites are social insects; many of them construct large edifices called termitaria and often spoken of as nests. A termitarium frequently contains an enormous number of individuals forming the society or colony. Termites are totally different in structure and development from all other social insects, but their social existence exhibits numerous analogies with that of the ants and other social Hymenoptera. The most remarkable of these analogies is that the reproduction of the species in each community is confined to a single pair, or to a very limited number of individuals.
Fig. 1.—A, newly hatched termite; B,
worker termite; Termes nemorosus.
The members of one society or colony, however numerous or dissimilar they may be, are the descendants a single pair. The colony is—so far as is known, and on this, as well as on many other points, authentic information is scanty—first started by a pair of winged individuals that cast their wings, secrete themselves in a suitable place, and produce young; the colony, however huge, being subsequently developed by the extreme productivity of the reproductive pair. Very little is known as to how long a colony endures, and, as there is great variety in the social conditions of different kinds of termites, it is probable that there is considerable difference as to the point in question. As a rule a family or colony has only a single termitarium, but there are cases in which a single family has several separate abodes, though usually only one of them is a real home containing reproductive individuals. The social life in termites, as well as in all other social insects, is clearly a development of the family life. It is accompanied by extraordinary modifications of the forms of the individuals constituting the society, and by a great division of labour.
Fig. 2.—A, mandibulate soldier of
Termes nemorosus; B, nasute soldier
of T. hospitalis.
As regards the forms, or castes, termites differ totally from other social insects; in the latter case there are great differences between the males and females, and the whole of the castes are of the female sex, whereas in termites the males and females are extremely similar, and the castes are in no way correlative with sex. As the termite life is a family life, and as there is normally only a single pair of reproductive individuals in each community, it is easily comprehensible that if anything goes wrong with this pair, the community is at once thrown into a state of complete disorganization. But this misfortune is mitigated by a method which termites have of keeping individuals in an undifferentiated state, and of turning some of them speedily into reproductive individuals, whereby the community is restored to something like a natural condition of activity and growth.
Apart from the forms that are merely juvenile, the following kinds, of adults are normally present in a colony: (1) workers, (2) soldiers, (3) winged individuals ready to leave the nest, (4) king and queen.
(1) The worker termite resembles the young in general appearance, and, like the young, has no trace of wings (fig. 1). The two segments behind the head are more contracted, so that head, thorax and abdomen are more differentiated than they are in the young. The colour too is different, the young being milky-white, whereas the adult worker is variously pigmented according to its species, but is never milky-white. The worker is generally blind, and in only a few species does it possess rudimentary eyes. The species of the group Calolermitides have no workers. In the other species the workers look after the eggs and young, and perform most, if not all, of the industrial work of the community. They are also, in some cases, effective combatants, though quite destitute of any special structures to suit them for this purpose. The sexual organs do not undergo development, but it has been satisfactorily ascertained that both sexes are represented amongst the workers. In certain species the workers seem to be dimorphic, so far as size is concerned, but this point has apparently been only very inadequately considered. Workers form a very large but variable proportion of the members of a community.
(2) The soldier termite is the most extraordinary feature of termite biology It is more varied than any of the other castes, so that most of the species of termites can be best distinguished by their soldiers. The chief feature of the soldier is an extraordinary development of the head, or of the head and mandibles. There are two very distinct kinds of soldiers: (a) the flat-headed or mandibulate soldier, and (b) the nasute or rostrate soldier (fig. 2). In the first kind the head is usually developed out of all proportion to the rest of the body; the mandibles are frequently enormous, and, being in many cases asymmetric, give the appearance of deformity. In the nasute soldier the head is thick or convex, and may be described as unicorn—that is to say, it is prolonged in the middle so as to form a single pointed horn; the mandibles are never largely developed. No species of termite has both mandibulate and nasute soldiers, although the reverse is sometimes still stated in books. The soldiers of some species are, however, dimorphic to the extent that larger and smaller forms occur in the same nest without intermediates. In other cases soldiers of simply variable size exist. The soldier is blind and wingless, though in a few soldiers minute wing-rudiments can be detected. As in the worker, the development of the sex organs is arrested, but both sexes are represented. The function of the soldiers is probably, as stated by Haviland, defence. The mandibulate soldiers use their heads as blocks to stop gaps in the nests, and employ terrifying but somewhat theatrical devices, making threatening motions and producing noises by movements of the head and thorax. The nasute soldiers emit a fluid from the tip of the rostrum, and dab it upon their enemies with some skill. Soldiers are present in all species of termites except the South American genus Anoplotermes. It is a remarkable fact that in the group Calotermitides soldiers exist although there are no workers, but in this case the function of the soldier seems to be very much that of a worker. Grassi says that in Calotermes flavicollis all the individuals of a community work for the common welfare. Moreover, in the Calotermitides no very great development of the heads or mandibles occurs.
(3) Adult or Winged Termite.—Such of the young as do not become workers or soldiers grow and develop after the fashion usual in exopterygote insects. Moults take place, the wing-pads gradually increase in size, eyes appear, and finally pigmentation takes place, and the winged insect is perfected at the last moult (fig. 3). In prosperous colonies these winged insects are produced in large numbers and emerge at intervals as swarms. They have extremely feeble powers of flight, and apparently scarcely any other capability. They are a favourite food of a large number of animals,
Fig. 3.—Adult Winged Termite: T. nemorosus; wings of the right-hand side expanded.
including even man They have well developed eyes and ocelli, and differ from all the other forms by their greater pigmentation The function of these adults is to diffuse the species, and to favour crossing outside the family circle. Attainment of this second end is, in some cases, favoured by the fact that the whole of the individuals constituting a swarm consist of one sex only. This extraordinary fact is attested by Grassi, but has not yet received the attention it merits. If a termite colony be compared with a tree or plant, the winged forms, it is clear, functionally correspond to the flowers and seeds of the tree; indeed, Fritz Muller and Grassi go further, and conclude that the modes of diffusion and reproduction of termites are analogous to the modes of plants of continuing the species by means of cleistogamic as well as ordinary flowers. The force of this comparison will be better appreciated after the reader has made himself acquainted with the facts connected with the neoteinic forms of termites.
(4) King and Queen.—As a rule each community includes only a single pair of individuals apt for reproduction; these are the royal pair, or king and queen (fig. 4). They are adult termites that have shed the wings they formerly possessed. The queen usually undergoes an extraordinary increase in the size of the abdomen, which may be distended to many hundred times its original capacity (fig. 4, A). In many species the king and queen are confined in a royal cell, out of which they cannot move, though the workers, owing to their smaller size, can get in and out to tend them. In other cases the queen only is so imprisoned, the king being able to leave the cell. In still other cases neither king nor queen is effectually imprisoned. Much discrepancy of opinion exists as to the invariable presence of a king in each nest; this, however, is explained by Haviland's observation that the king is active and timid, and when a nest is opened seeks safety by running away and concealing himself, so that he is sometimes only discovered when the very last fragment of the nest is brought under scrutiny. Another point on which extremely diverse opinions are expressed is the copula of the sexes. It is usually stated that the swarming of termites is analogous to that of bees and ants, in which groups of insects the conjunction of the sexes takes place at this period, and at this period only. In the termites the reverse is the case. The swarming is not at all a nuptial flight; indeed, at that time the sexes are not apt for reproduction. Copulation only takes place after a pair have cast their wings and have established themselves together. It is repeated at intervals, and is thus quite dissimilar from the corresponding phenomenon in Hymenoptera. The male has no intromittent organs, so that copula during flight is impossible. Grassi has actually witnessed the act in subsequent life. Haviland is of opinion that in some cases the male fertilizes the eggs without connexion with the female.
(5) Neoteinic and Substitution Forms.—When a colony of termites is deprived of king and queen it can replace them by forms specially prepared. These substitution forms are of two kinds—(a) normal adult individuals, and (b) neoteinic forms. The latter may be described as unnatural kings and queens possessing reproductive powers, though the wings have never been developed and some other parts of the body have not taken on the fully adult state. Haviland removed the royal pairs from nests of Termes malayanus, and after three or four months again examined the nests: in three out of the five cases substitution pairs exactly resembling the original ones, with well-formed wing-stumps, were present; in the other two cases he failed to find the royal cell, and believes that the loss had not been repaired. In other species the bereavement is made good by means of neoteinic instead of normal individuals, and in certain species neoteinic forms are abundantly found. In the case of substitution forms there is usually more than one pair present in a colony, and sometimes numerous pairs exist. Grassi says that in Sicily the colonies of Termes lucifugus are kept up entirely by neoteinic kings
Fig. 4.—A, queen; B, king: T. nemorosus.
and queens; in other words, the swarms are nearly or quite useless. The neoteinic forms are compared to cleistogamous flowers; and this curious case is parallel with that of a species of plant whose reproduction should be accomplished entirely by its cleistogamous flowers, though at the same time it produced perfect flowers up in abundance. The condition recorded by Grassi is probably extremely exceptional. Fritz Müller found once a colony in which a true king was acting as consort to a considerable number of neoteinic queens, no true queen being present. In order to understand the curious phenomena presented by the castes and variety of forms of a single species of termite, it is necessary to become acquainted with their food habits, which are very peculiar and may be described as communistic. Termites have the habit of eating their cast skins and even their dead companions, and in fact their system of keeping the nest clean seems to be that of eating the refuse of their own bodies till it no longer contains any digestible matter. This cannibalism is the more remarkable, as the will not eat other termites. The most curious part of their dietary is their complex system of feeding from the matters contained in the alimentary systems of their fellows. When a termite wishes food it strokes the body of another individual with its antennae, and the specimen thus caressed exudes from the posterior or from the anterior part of the body a drop of matter, which is eaten by the hungry one. The matter exuded from the posterior part of the body appears to be very different from that yielded by the mouth, so that there are at least two kinds of this excretory food. The proctodaeal food (that which comes from the posterior part of the body) is in great favour with adult termites, ut so far as is known it is not used for feeding the newly born young, which are believed to be fed on matter elaborated in the bodies of the adult workers and communicated by their mouths. Subsequently the young take also proctodaeal food, and triturated vegetable matter.
Origin of the Castes.—When termites are hatched from the eggs none of the remarkable differences that are manifested in the individuals in subsequent life can be detected. The sexes are in termites extremely similar in external characters. When the young are hatched they all appear nearly exactly alike, though on careful examination the sexes can be distinguished But no other difference than that of sex can be detected. In the article Ant in the ninth edition of the Encyclopaedia Britannica it was stated that “the distinction between soldier and worker can be easily seen in the egg.” This is contradicted by all modern observations, and is certainly erroneous. It is true that considerable difference of opinion exists as to when the distinction between soldier and worker first becomes evident, but all are agreed that it is not till after the growth is to some extent accomplished. The discrepancy that exists in opinions on this point is due to the facts: (1) that different species have been under observation; and (2) that the modification of the larva to form a soldier may begin at more than one period of the development even in the same species. It being ascertained that all termites begin as undifferentiated larvae, the question arises as to what causes the differentiation into castes. This question is the more important as two of the castes (the worker and soldier) do not at all resemble their parents. Grassi, from an examination of the individuals of a large number of nests of Termes lucifugus, arrived at the conclusion that all start as undifferentiated larvae, and that the regular development of Termes up to the perfect insect may undergo a deviation at various periods of life leading to the formation of workers, of neoteinic forms, or of soldiers, the last passing through the stage of the young worker. He attributes this deviation, which may take place at various periods, to the influence of food, and attaches special importance to the salivary food. The soldiers have no wings; nevertheless a larva, or young nymph that has the rudiments of wings, can be made into a soldier. Grassi has found juvenile specimens that have already assumed the soldier form, although they possess the rudiments of wings. It appears from his observations that the worker may be considered as a form with arrested development, and the soldier as a form with arrested and much diverted development, while the neoteinic forms are individuals in which the reproductive organs are perfectly developed, while some of the bodily structures have suffered arrest of development and even some amount of atrophy.
Fig. 5.—Termitarium of Termes malayanus: f, fungus-chamber; c, royal cell.
The soldier form of termite presents most difficult questions to the biologist, its special structures bearing no approximation to any characters possessed by the parents. Various theories have been proposed to account for this fact, but they are mere guesses. We may, however, mention that it is possible that soldiers and workers occasionally produce young. This has never been actually observed, but specimens have been found with the sexual organs partially developed, and F. Silvestri has recorded the occurrence of workers with some of the characters of the females, in South America, in a nest of Termes strunchii.
Termitaria.—There is nothing in which termites display more variety than in their dwellings. These are sometimes not constructions at all. The primitive Calotermes flavicollis—in which there is no worker—frequently inhabits rotten places in trees; at most it increases these a little by excavation, and modifies the passages by slight and imperfect barricades. In the case of this species the community never attains a greater number than one thousand individuals, and even this is comparatively rare. On the other hand, we have the huge solid structures, 10 or 20 ft. high, delineated by Smeathman with cattle standing on their summits. Saville Kent has observed termitaria in Australia 18 ft. high. In equatorial Africa termitaria are frequently 12 to 25 ft. high and sharp-pointed. As a rule large termitaria do not occur in considerable numbers in a restricted area, but there are exceptions even to this. At Somerset, Cape York, there is one of the most remarkable termite cities of the world. Viewed from the sea, it appears as if the plain for a mile or more in extent were covered with pointed pillars, varying, according to different accounts, from 6 to 13 ft. in height, broad at the base and tapering to the summit, forming regular symmetrical pyramids. In this part of Australia there is also found the “compass,” “magnetic,” or “meridian” termite, the mounds of which have somewhat the shape of a tombstone, and have always the same orientation, the wider face of the structure always extending north to south. It has been suggested that this is connected with the necessity of regulating the temperature or the amount of desiccation of the nest, but there is no evidence whatever on the point. A termitarium on being opened displays a vast number of irregular chambers separated by thin partitions (fig. 5, f), the royal cell being placed in the middle (fig. 5, c). The material used is of an earthy nature, but the interiors of many earthy termitaria are largely composed of woody fibre, the refuse proceeding from the alimentary canals of the insects being used for this purpose. A considerable number of the larger termites use fungi for their foodstuff. There are special chambers where these are cultivated, the matter on which the fungus is grown being of a woody nature and sponge-like in its structure. The fungi make their appearance as small globules. Probably the spores or mycelium are placed in the mass when it is formed by the termites; but very little is yet known as to this fungus and its mode of treatment by them.
Authorities.—H. Smeathman, “Termites,” Phil. Trans. (1781), pt. i. lxxi., pp. 139-192; H. Hagen, “Monograph of Termites,” Linnaea Entomologica, 1855 and 1860, x. and xiv.; G. D. Haviland, “Observations on Termites,” J. Linn. Soc. Zool. (1898), xxvi., 358-442; B. Grassi and A. Sandias, “The Constitution and Development of the Society of Termites,” Atti Acc. Gioenia (4), 1893 and 1894, vi. and vii.; translated by W. F. H. Blandford in Q. J. M. S. (1897), xxxix. and xl.; Y. Sjöstedt, “Monographie der Termiten Afrikas,” K. Svenska Vet.-Ak. Handl. (1900), xxxiv., No. 4; W. W. Froggatt, “Australian Termitidae” (three parts), P. Linn. Soc. N.S. Wales, 1895, 1896, 1897; W. S. Kent, The Naturalist in Australia (London, 1897), iv. Extensive bibliographies are given by Hagen and Sjöstedt. (D. S.*)