When the animals find a place favorable to their vital needs, they establish themselves there in small colonies and live side by side without bothering about their neighbors. Thus do the Ocypodes, the Gelasimas, and certain other crabs which live in the shore sand, the Coleoptera of the genus Cicindela, which dig their burrows in clay soils. Thus also do the nesting Hymenoptera: Bembex and Philanthus among the predatory species, Andrena, Halictus, Chali-codoma, and Anthophora among the solitary bees. Even in these groups all species are not equally sociable: thus our Chalicodoma of the walls constructs its mass of cells solitarily, while Chalicodoma pyrenica likes to have its nest near others. Fabre says:
I have seen some of these nests (colonies) which, under the tiles of a shed, occupied a surface of five or six square meters. ... It is necessary to see the active bee at work.
. . . Between the farmyard where they were building, and the road where they were preparing the mortar, the sound of the murmur of the arriving and the departing bees increased without interruption. The air seemed traversed by continual streaks of smoke, so direct and rapid is the trail of the travelers.
Having the same habits as their progenitors, the young find it profitable to establish themselves in the place where their parents nested. They nest there in their turn and so give birth to a society where all the individuals are attached to a common locality; strangers having the same habits also come to make their nests in the same place, and the colony is composed of several juxtaposed families. The same thing occurs with the Chalico-doma of the Pyrenees, studied by Fabre, and with the African solitary wasp of the genus Synagris, studied by Roubaud;1 in fact, individualist societies are almost always the beginnings of family groups. Different circumstances, moreover, favor groups of this sort, among others the habit that certain young have of remaining at the maternal nest until the moment when it becomes necessary for them to work in their turn. I have described (1916) this habit in our Philanthus trian-gulum, and the Peckhams have made similar observations with an American species, Philanthus punctatus. What favors still more the formation of these family individualist groups is the laying of a large number of eggs at the same point of the nutritive subtratum. When the young issuing from these eggs have not the usual industry, they content themselves with remaining in the neighborhood upon the substratum, as is observed with the caterpillar of the cabbage butterfly (Pieris brassic). But if they have in addition the power of spinning a silken thread, they can associate their talents and together make a protective web which they leave at certain hours individually to satisfy their needs. This is done by an American Pierid, Eucheira socialis, which constructs a very spacious web, remarkable for the resistance and close webbing of its walls. This is also done by many caterpillars of nocturnal moths, among others the processionaries and several Bombycids and the Hypomomeutas.
1 E. Roubaud, Recherches bioligiques sur les Guêpes sociales et solitaires d'Afrique. (Ann. 8c. Nat., Zool. ser. 10. v., pp. 1-160, 1916).
Spiders are known for their sanguinary instincts and for the cannibalism which they practise either at ordinary times when they are kept in the same cage, or at the rutting period, when certain females have no scruples about devouring their lovers. But these murderous instincts develop only with age ; on leaving the cocoon the young of the same hatching live in perfect harmony and associate their talents as spinners to make a common nest. This pacific humor persists with certain species,-rare, it is true,-and they continue the building of common webs in which they live and bring forth numerous individuals. Eugene Simon1 has mentioned several of these sociable spiders, among others an American The-ridiid, Anelosimus socialis, whose common web sometimes covers an entire coffee tree. "The spiders walk about there freely," observes the author, "meeting one another and tapping with their palpi as the ants do with their antennae, and more often devouring a smaller prey." Sem-ichon (1909) has mentioned the same fraternal dwelling together of a social Mexican spider, Cnothele gregalis, brought to the Museum by Leon Diguet (1909). This species makes upon trees vast social webs which it develops concentrically with spun threads which are to capture insects. Thousands of individuals live in perfect harmony in this immense pocketed sack, and never go out except after the rainy season, when they emigrate,-I was about to say swarm,-to leave room for the young. These nests divided and, suspended to the ceiling, act as traps for flies in certain parts of Mexico. One of them, exposed in the galleries of the museum [in Paris], reached the length of several meters.
Between the individualist groups of Gelasimas, Ocypods, and Cicindelids, where each one hunts on his own account, and those of the preceding social spiders, which spin a common web, and often divide their captures, there are a quantity of steps of which caterpillars and Hymenoptera offer examples. Even in the simple individualist colonies of Hymenoptera one observes a kind of espirit de corps when it is necessary to struggle for the common defense. In such a case, the Anthophora of the walls become singularly aggressive; established in sandy argillaceous soil which it perforates with tubular galleries, this bee comes out in war-like swarms every time one approaches the colonies; Buttel-Reepen (1903) relates the misadventure of an entomologist who was pursued a long time by one of these swarms after a badly executed swing of his net ; and Friese reports that he himself was attacked for having tried to collect on the walls of a barn where thousands of Antho-phoras had established their nests. It is a crowd reflex, Buttel-Reepen justly remarks, a reflex which is never produced when one attacks isolated individuals or small groups.
1 E. Simon, Voyage au Venezuela: les Araignées sociables, 1891. [Ann. Soc. Ent. France, v. 60, pp. 5-14).