species, as our small yellow meadow ants, the autumn larvæ remain with comparatively little change throughout the winter. It is much more difficult to ascertain the length of life of the perfect insect, on account of their gregarious habits, and the difficulty of recognizing individual ants. It has, however, generally been supposed that they live about a season, and this is probably the case; but I have still some workers of F. cinerea, which I captured at Castellamare in November, 1875, and some of F. sanguinea and F. fusca since September in that year. They must now, therefore, be at least a year and a half old. I have also some queens of F. fusca which have been with me since December, 1874, and still seem in perfect health. If they lived much longer, and could compare their experiences, ants would, from their immense numbers, even in temperate regions, contend with mankind on no such very unequal terms.
The behavior of ants to one another differs very much according as they are alone or supported by numerous companions. An ant which would run away in the first case, will fight bravely in the second.
It is hardly necessary to say that, as a general rule, each species lives by itself. There are, however, some interesting exceptions. The little Stenamma Westwoodii is found exclusively in the nests of the much larger F. rufa and the allied F. pratensis. We do not know what the relations between the two species are. The Stenammas, however, follow the Formicas when they change their nest, running about among them and between their legs, tapping them inquisitively with their antennæ, and even sometimes climbing on to their backs, as if for a ride, while the large ants seem to take little notice of them. They almost seem to be the dogs—or rather cats—of the ants. Another small species, Solenopsis fugax, which makes its chambers and galleries in the walls of the nests of larger species, is the bitter enemy of its hosts. The latter cannot get at them, because they are too large to enter the galleries. The little Solenopsis, therefore, are quite safe, and, as it appears, make incursions into the nurseries of the larger ant, and carry off the larvæ as food. It is as if we had small dwarfs, about eighteen inches to two feet long, harboring in the walls of our houses, and every now and then carrying off some of our children into their horrid dens.
Most ants, indeed, will carry off the larvæ and pupæ of others if they get a chance; and this explains, or at any rate throws some light upon, that most remarkable phenomenon, the existence of slavery among ants. If you place a number of larvæ and pupæ in front of a nest of the horse ant, for instance, they are soon carried off; and those which are not immediately required for food remain alive for some days, though I have never been able to satisfy myself whether they are fed by their captors. Both the horse ant and the slave ant (F. fusca) are abundant species, and it must not unfrequently occur that the former, being pressed for food, attack the latter and carry off