arvae. Those species that feed
close to the surface and have the tip of the breathing-tube above the
surface most of the time have very small tracheal gills, while those
that feed mostly on the bottom have them well developed.

When first hatched the larvae are of course very small. If the weather is
warm and the food is abundant they grow very rapidly. In a few days the
outer skin becomes rather firm and inelastic so it will not allow
further growth. Then a new skin forms underneath and the old skin is
cast off. This process of casting off the old skin is called molting,
and is repeated four times during the one, two, three or more weeks of
larval life.

PUPA

With the fourth molt the active feeding larva changes to the still
active but non-feeding pupa (Fig. 59). The head and thorax are closely
united and a close inspection will reveal the head, antennae, wings and
legs of the adult mosquito folded away beneath the pupal skin. Instead
of the breathing-tube on the eighth segment of the abdomen as in the
larva, the pupa has two trumpet-shaped tubes on the back of the thorax
through which it now gets its air from above the surface. The pupal
stage lasts from two to five or six days or more. When the adult is
ready to issue the pupal skin splits along the back and the mosquito
gradually and slowly issues. It usually takes several minutes for the
adult to issue and for its wings to become hard enough so it can fly. In
the meantime, it is resting on the old pupal skin or on the surface of
the water, where it is entirely at the mercy of any of its enemies that
might happen along and is in constant danger of being tumbled over
should the water not be perfectly smooth.

[Illustration: FIG. 59--Mosquito pupae (_T. incidens_) resting at the
surface of the water.]

[Illustration: FIG. 60--Mosquito pupa (_T. incidens_) with its
breathing-tubes in an air bubble below the surface of the water.]

[Illustration: FIG. 61--Mosquito larvae and pupae (_T. incidens_) resting
at the surface of the water.]

[Illustration: FIG. 62--A female mosquito (_T. incidens_); note the
thread-like antennae.]

[Illustration: FIG. 63--A male mosquito (_T. incidens_); note the
feathery antennae.]

THE ADULT

The adult mosquito is altogether too familiar an object to need
description, but it is necessary that we keep in mind certain particular
points in regard to its structure, in order that we may better
understand how it is that it is ca