GENERAL REMARKS ON INSECT SOCIETIES It is a remarkable fact, as Wheeler remarks, that among insects social habits have arisen no less than 24 different times in as many different groups of solitary insects. The various examples of this type of behaviour represent, as has already been pointed out, very different stages in the evolution of their social system. In the simplest cases only mere rudiments of social behaviour are evi dent, while at the other extreme are highly organized systems in volving immensely populous communities, presenting many sim ilarities or analogies to human society. Several writers have corn pared an insect society to a super-organism and, as Julian Huxley has remarked, the members of the community, although now func tioning as parts, were descended from ancestors that functioned as wholes. The castes exhibit a differentiation of structure and func tion corresponding with the division of labour among the organs of an animal body. A single individual is incapable of prolonged survival apart from other members of an insect community, almost as the separate organs of an animal body are incapable of independent existence. The workers and soldiers may be looked upon as the body of the super-organism, while the fertile mem bers, representing the germ cells, form the organism that ensures the continuance of the species.
One of the most urgent difficulties in communal life is the supply of food. The members of a colony need a regular, abundant and easily available source of nourishment. Certain of the smaller and more primitive insect societies feed upon animal food, but the more highly organized and densely populated colonies of other species as a rule resort to the more certain and abundant supplies afforded by the plant kingdom. The collecting and apportioning of food among adults and young, economy in its use and com petition with other organisms in securing supplies, all seem to have contributed to the development Of a special worker caste upon whom the onus of provisioning the colony rests. The re productive instincts likewise present profound difficulties in com munal life : unlimited exercise of this faculty would result in a population speedily overreaching its food supply and finally the disintegration of social life. The true social insects have overcome
this difficulty because among them the full reproductive powers are confined to few individuals and aborted in the rest. Among the social Hymenoptera the colonies are essentially gynarchic, the female being the dominant sex: under this regime the males, apart from breeding purposes, are little more than social parasites. In the hive bee it is well known that after fertilization of the queen is achieved the luckless males are eventually driven out of the hive. On the other hand, among termites, as we have seen, both sexes participate in the life of the society, and in this respect they more closely resemble the human species.
The onset of social life has led to the development of com munal nests wherein security is afforded to the inmates. The helpless, sedentary brood, massed together, is naturally fixed to a particular location and exposed to the attacks of enemies and changes of the elements. The need consequently arose for pro tective habitations or even fortifications of various types suited for special requirements. Those social Hymenoptera, endowed with wings and adequate stings, chiefly nest above ground while the largely wingless, and on the whole more defenceless, ants and termites have mainly sought protection in a subterranean life. Social insects are highly successful in the struggle for ex istence, as is exemplified by their abundance in individuals, as well as by the great variety of habitats they occupy and the extent to which such creatures as ants and termites have spread over the world. Tending of the brood by social insects has led to the intimate relationship that exists between the two generations, and consequently to the discovery by the parents of the palatability of the salivary or other secretions of their young. In this way trophallaxis or mutual feeding, previously quoted, has arisen, and the avidity of the parents for what their young have to offer them has developed in so many cases into a bond which has ex tended and strengthened social behaviour.