rarely or never quit the nest, but receive their food from the workers, and indeed appear to do nothing except lay eggs.
A nest of ants must not be confused with an ant-hill in the ordinary sense. Very often, indeed, a nest has only one dwelling, and in most species seldom more than three or four. Some, however, form numerous colonies. M. Forel even found a case in which one nest of F. exsecta had no less than two hundred colonies, and occupied a circular space with a radius of nearly two hundred yards. Within this area they had exterminated all the other ants, except a few nests of Tapinoma erraticum, which survived, thanks to their great agility. In these cases the number of ants thus associated together must have been enormous. Even in single nests Forel estimates the numbers at from 5,000 to 500,000.
In their modes of fighting, different species of ants have their several peculiarities. Some, also, are much less military than others. Myrmecina Latreillii, for instance, never attack, and scarcely even defend themselves. Their skin is very hard, and they roll themselves into a ball, not defending themselves even if their nest is invaded: to prevent which, however, they make the entrances small, and often station at each a worker, who uses her head to stop the way. The smell of this species is also, perhaps, a protection. Tetramorium cæspitum has the habit of feigning death. This species, however, does not roll itself up, but merely applies its legs and antennæ closely to the body.
Formica rufa, the common horse ant, attacks in serried masses, seldom sending out detachments, while single ants scarcely ever make individual attacks. They rarely pursue a flying foe, but give no quarter, killing as many enemies as possible, and never hesitating, with this object, to sacrifice themselves for the common good.
Formica sanguinea, on the contrary, at least in their slave-making expeditions, attempt rather to terrify than to kill. Indeed, when they are invading a nest, they do not attack the flying inhabitants unless they are attempting to carry off pupæ, in which case they are forced to abandon the pupæ. When fighting, they attempt to crush their enemies with their mandibles.
Formica exsecta is a delicate but very active species. They, also, advance in serried masses, but in close quarters they bite right and left, dancing about to avoid being bitten themselves. When fighting with larger species they spring on to their backs, and then seize them by the neck or by an antenna. They also have the instinct of combining in small parties, three or four seizing an enemy at once, and then pulling different ways, so that she, on her part, cannot get at any one of her foes. One of them then jumps on her back and cuts, or rather saws, off her head. In battles between this ant and the much larger F. pratensis, many of the latter may be seen, each with a little F. exsecta on her back, sawing off her head from behind.
