BACOT : MOSQUITOES AND THE DANGER OF MALARIA. 243
to man than any other group. To this order belong such proved
carriers and distributors of disease-germs as the House and Blow-
flies ; also the numerous biting species—Tabanids, Stable flies,
Tsetse flies, Blood-sucking midges, etc. The mosquitoes form,
from man's paint of view, the crowning infamy of the Diptera.
The actual theft of blood from their victims is a very minor
matter, compared with the irritation caused by the injection
of their saliva into the wound ; while in the background lurks
the danger of inoculation with some disease-germ introduced
during the process of feeding. Agriculturists, again, have to
deplore the inroads made by dipterous larvae on growing crops.
It is true that some of the two-winged flies are Ishmaels and
destroy their relatives, but it is doubtful if these species com-
pensate for a tithe of the harm wrought by their fellows.
Like all the groups of insects belonging to the order Diptera,
the mosquitoes undergo a complete metamorphosis during the
period of development from egg to adult, the larvae hatching
from the eggs being entirely different in form and habit from
their parents.
The Eggs.—Female mosquitoes usually lay their eggs on
the water-surface or the wet margins of a pool, occasionally
on wet mud. The instincts of certain northern species lead
them to deposit their eggs in the bottom of dry hollows, which
are converted into pools only in the following spring by the
melting of the winter snow ; but no English mosquitoes are
known to have this habit.
The eggs may be deposited singly or attached together in the
form of rafts, which float upon the surface of the water, head end
downwards, according to the species laying them. Those laid
singly on water may either sink, float, or become stranded on
the margins of the pool ; and, in accordance with their specific
nature, individual constitution, or treatment, they may either
hatch promptly or the larvae may defer emergence from the
shell for a long period after incubation. It seems, however,
a constant rule that eggs of the species which cement them
together to form a raft must hatch promptly or perish.
The Larva, though adapted for an aquatic life only, may
survive in some cases for several days in wet mud, but are
unable to complete their development in the absence of sufficient
water to swim in. In feeding, they seem to rely chiefly upon