,
caterpillars of blue butterflies (_Lycaenidae_), and numerous beetles,
furnish the ants with nutrient secretions. The number of species of
beetles that inhabit ants' nests is almost incredibly large, and most of
these are never found elsewhere, being blind, helpless and dependent on
the ants' care for protection and food; these beetles belong for the
most part to the families _Pselaphidae, Paussidae_ and _Staphylinidae_.
Spring-tails and bristle-tails (order _Aptera_) of several species also
frequent ants' nests. While some of these "guest" insects produce
secretions that furnish the ants with food, some seem to be useless
inmates of the nest, obtaining food from the ants and giving nothing in
return. Others again play the part of thieves in the ant society; C.
Janet observed a small bristle-tail (_Lepismima_) to lurk beneath the
heads of two Lasius workers, while one passed food to the other, in
order to steal the drop of nourishment and to make off with it. The same
naturalist describes the association with Lasius of small mites
(_Antennophorus_) which are carried about by the worker ants, one of
which may have a mite beneath her mouth, and another on either side of
her abdomen. On patting their carrier or some passing ant, the mites are
supplied with food, no service being rendered by them in return for the
ants' care. Perhaps the ants derive from these seemingly useless guests
the same satisfaction as we obtain by keeping pet animals. Recent
advance in our knowledge of the guests and associates of ants is due
principally to E. Wasmann, who has compiled a list of nearly 1500
species of insects, arachnids and crustaceans, inhabiting ants' nests.
The warmth, shelter and abundant food in the nests, due both to the
fresh supplies brought in by the ants and to the large amount of waste
matter that accumulates, must prove strongly attractive to the various
"guests." Some of the inmates of ants' nests are here for the purpose of
preying upon the ants or their larvae, so that we find all kinds of
relations between the owners of the nests and their companions, from
mutual benefit to active hostility.

Among these associations or guests other species of ants are not
wanting. For example, a minute species (_Solenopsis fugax_) lives in a
compound nest with various species of _Formica_, forming narrow
galleries which open into the larger galleries of its host. The
_Solenopsis_ can make its way into the territory of the _Formica