find the desolated nest in the thick heath. The nest, however, must have
been close at hand, for two or three individuals of F. fusca were rushing
about in the greatest agitation, and one was perched motionless with its
own pupa in its mouth on the top of a spray of heath, an image of despair
over its ravaged home.

Such are the facts, though they did not need confirmation by me, in regard
to the wonderful instinct of making slaves. Let it be observed what a
contrast the instinctive habits of F. sanguinea present with those of the
continental F. rufescens. The latter does not build its own nest, does not
determine its own migrations, does not collect food for itself or its
young, and cannot even feed itself: it is absolutely dependent on its
numerous slaves. Formica sanguinea, on the other hand, possesses much
fewer slaves, and in the early part of the summer extremely few. The
masters determine when and where a new nest shall be formed, and when they
migrate, the masters carry the slaves. Both in Switzerland and England the
slaves seem to have the exclusive care of the larvae, and the masters alone
go on slave-making expeditions. In Switzerland the slaves and masters work
together, making and bringing materials for the nest: both, but chiefly
the slaves, tend and milk as it may be called, their aphides; and thus both
collect food for the community. In England the masters alone usually leave
the nest to collect building materials and food for themselves, their
slaves and larvae. So that the masters in this country receive much less
service from their slaves than they do in Switzerland.

By what steps the instinct of F. sanguinea originated I will not pretend to
conjecture. But as ants which are not slave-makers, will, as I have seen,
carry off pupae of other species, if scattered near their nests, it is
possible that such pupae originally stored as food might become developed;
and the foreign ants thus unintentionally reared would then follow their