BACOT : MOSQUITOES AND THE DANGER OF MALARIA. 259
readiness or movement of its hind legs. Larvae and pupae
of mosquitoes are devoured by fish, newts, water-beetles and
their larvae, by dragon-fly larvae, by various species of water-bugs,
and by the larvae of some species of ephemerids. There are,
further, the cannibal larvae of their near relatives and allied
groups, which are by no means the least dangerous of their
foes. Competitors for the food they need while in the larval
stage also check the increase of the mosquitoes. In some instances,
these competitors are so numerous and so efficient as to starve
the larvae ; in other cases, they increase their danger from other
enemies by prolonging the larval period. Tadpoles and water-
snails in the larger ponds devour the raw material from which
their food would be developed. Small crustacea and the larvae
of Chironomus are so efficient as scavengers in small collections
of water that they may actually starve the mosquito larvae.
VI.—Methods for the Combating of Mosquitoes by Man.
The inventions of man for combating mosquitoes may be
summarised as follows :—The use of mosquito curtains ; the
screening of dwellings ; the use of preparations to prevent the
insects biting ; the destruction of adults by traps, fumigation,
or spraying ; the removal of cover near houses ; and the cutting
of trees, bushes, and grass. Further, mosquitoes are open to
attack in the larval and pupal stages by the drainage of surface-
water and swamps, the filling of pools and water-holes, the
removal of weeds in streams and ponds, the deepening of the
margins of ponds, the filling of hoof-holes, the oiling of water-
surfaces, and the penalising of persons who allow mosquitoes to
breed in lily-ponds, rock-gardens, swamps, water-tanks, water-
butts, and other domestic supplies of water, and those who leave
about discarded tins and empty bottles.
Before deciding upon the most suitable methods of control
for any district, careful consideration must be given to their
effect on, or interaction with, any of the natural enemies of the
mosquito. If this is not done, more harm than good may re-
sult. For instance, the filling of a pond may destroy a breeding
place for their enemies (such as water-beetles, dragon-flies,
newts, toads, frogs, etc.), with the result that the numbers of
these may be reduced. The gain resulting from the removal of a
breeding place in which relatively only a very few of the mosquito