of the
ant has come down in English from a thousand years ago shows that this
class of insects impressed the old inhabitants of England as they
impressed the Hebrews and Greeks. The social instincts and industrious
habits of ants have always made them favourite objects of study, and a
vast amount of literature has accumulated on the subject of their
structure and their modes of life.

_Characters._--An ant is easily recognized both by the casual observer
and by the student of insects. Ants form a distinct and natural family
(_Formicidae_) of the great order _Hymenoptera_, to which bees, wasps
and sawflies also belong. The insects of this order have mandibles
adapted for biting, and two pairs of membranous wings are usually
present; the first abdominal segment (propodeum) becomes closely
associated with the fore-body (thorax), of which it appears to form a
part. In all ants the second (apparently the first) abdominal segment is
very markedly constricted at its front and hind edges, so that it forms
a "node" at the base of the hind-body (fig. 1), and in many ants the
third abdominal segment is similarly "nodular" in form (fig. 3, _b,
c._). It is this peculiar "waist" that catches the eye of the observer,
and makes the insects so easy of recognition. Another conspicuous and
well-known feature of ants is the wingless condition of the "workers,"
as the specialized females, with undeveloped ovaries, which form the
largest proportion of the population of ant-communities, are called.
Such "workers" are essential to the formation of a social community of
Hymenoptera, and their wingless condition among the ants shows that
their specialization has been carried further in this family than among
the wasps and bees. Further, while among wasps and bees we find some
solitary and some social genera, the ants as a family are social, though
some aberrant species are dependent on the workers of other ants. It is
interesting and suggestive that in a few families of digging Hymenoptera
(such as the _Mutillidae_), allied to the ants, the females are
wingless. The perfect female or "queen" ants (figs. 1, 1, 3, a) often
cast their wings (fig. 3, b) after the nuptial flight; in a few species
the females, and in still fewer the males, never develop wings. (For the
so-called "white ants," which belong to an order far removed from the
_Hymenoptera_, see TERMITE.)

[Illustration: FIG. 1.--Wood Ant (_Formica rufa_). 1, Queen; 2, male; 3,
worker.]