The Cambridge natural history, Vol. 05 (of 10)

by Adam Sedgwick; David Sharp; F. G. Sinclair

Forms of Termes lucifugus. (After Grassi.) Zool. Anz. xii. 1889, p. 360.

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, 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 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. 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.