A butterfly or a moth is primarily egoistic and unsocial in the ordinary sense during its entire life-history, until the final reproductive act which has a value to the species. The caterpillar larva devotes all of its energies to feeding and growing, unconcerned with the final duties of the moth with which it is connected just as the indifferent unit of a young _Volvox_ colony is related to a reproducing member of the full-grown organism. Now and then, it is true, species like the so-called tent caterpillar are met with where numerous larvæ spin silken communal nests to which they retire at night and in which they remain to molt. The pupa, like the larva, is individualistic and employs its time in producing the final adult form. The mature individual, however, is constructed almost solely for the greater purpose of perpetuating the species. Indeed the larger silkworm moths do not and cannot feed, and their value is only that of a device for keeping the race established. Adult may-flies live only a few minutes, just long enough to provide for the fertilization and deposition of the eggs, although to prepare for these acts the young individuals must have toiled for months; the preparatory time may amount to many years in such a case as the seventeen-year locust. But nature is satisfied, as long as the organic mechanisms obey her double commandment, "Live and grow so as to multiply." Like an _Amoeba_, the solitary insect must be egoistic at first, in order to be altruistic in a racial sense in its last days.
Wasps, bees, and ants provide many familiar examples of colonial organizations that become all the more marvelous on closer acquaintance, on account of their resemblances to human associations on the one hand, and to cell-associations on the other. Their illustrative beauty is enhanced by their wide variety, for they grade from counterparts of highly civilized men down to a savage among insects, such as the strictly solitary digger-wasp, whose instincts served to exemplify the insect type of "mentality" in the discussions of the preceding chapter.
The true communities founded by wasps and hornets must be assigned to a low grade in the scale because they originate during a single season and break up at its end; for this very reason the wasp community is intensely interesting to the student of comparative social evolution. In the spring a solitary female emerges from the crevice where she has hibernated and resumes active life; she feeds for a time to renew her strength and then she constructs a simple nest of mud or masticated wood-pulp. In the first few cells of this nest she deposits her eggs, and when they hatch she herself provides the larvæ with food, but still continues to enlarge the house and to produce more eggs. Thus during the first few weeks of the colony's existence this single individual performs a variety of tasks of racial as well as of purely egoistic value; but as time goes on, a profound change comes about in her activities and in the life of the whole community. The members of the first brood do not grow into counterparts of their mother; they are all sexless "workers" who progressively relieve their parent of the tasks of nest-building and foraging and nursing, so that their mother becomes a "queen" who devotes her entire time to the special reproductive task which she only can perform. We may justly compare the queen to the reproductive organ of _Hydra_, for the values to the life of the species are identical in the two cases, while the various classes of workers are counterparts of such units as the muscle and nerve and nutritive components of the _Hydra_ or any other cell-community individual. Another resemblance between the two is found in the death of all the sexless individuals at the end of the season, when reproducing males and females are finally formed, of whom the fertile queens only survive in their winter hiding places; and again we can discover the cause for biological death in that division of labor which calls upon certain members of the whole community to perform tasks that have no value when once provision has been made for perpetuating the species. Finally the mode by which the colony grows and amplifies is in all respects like the embryonic development of an egg into a _Hydra_, so that we may add the phrase "social embryology" to our vocabulary. The original female is an undifferentiated master of all trades; the small tribe she first establishes is little better off than a horde of savages; but during its seasonal existence the community increases in numbers and complexity until it advances well toward the civilized condition, when each class performs its special task for the good of all.