different paths; and this difficulty makes it absolutely necessary for
the Amazons to return by the same road by which they went. The insect
has no choice of route, if it would not be lost on the way: it must
come back by the track which it knows and which it has lately
travelled. The Processionary Caterpillars, when they leave their nest
and go to another branch, on another tree, in search of a type of leaf
more to their taste, carpet the course with silk and are able to
return home by following the threads stretched along their road. This
is the most elementary method open to the insect liable to stray on
its excursions: a silken path brings it home again. The
Processionaries, with their unsophisticated traffic-laws, are very
different from the Mason-bees and others, who have a special sense to
guide them.

The Amazon, though belonging to the Hymenopteron clan, herself
possesses rather limited homing-faculties, as witness her compulsory
return by her former trail. Can she imitate, to a certain extent, the
Processionaries' method, that is to say, does she leave, along the
road traversed, not a series of conducting threads, for she is not
equipped for that work, but some odorous emanation, for instance some
formic scent, which would allow her to guide herself by means of the
olfactory sense? This view is pretty generally accepted. The Ants,
people say, are guided by the sense of smell; and this sense of smell
appears to have its seat in the antennae, which we see in continual
palpitation. It is doubtless very reprehensible, but I must admit that
the theory does not inspire me with overwhelming enthusiasm. In the
first place, I have my suspicions about a sense of smell seated in the
antennae: I have given my reasons before; and, next, I hope to prove
by experiment that the Red Ants are not guided by a scent of any kind.