74
dangerous anopheles. The adult mosquito is very large and is coloured a dull
black and white. Its larvæ resemble very large Stegomyia larvæ and assume
the same position in water, hanging nearly perpendicular with the head down-
wards. They breed in very foul water and on one occasion many hundred were
found in a vessel containing; stale urine.
Several other species of mosquitoes, mostly Culicines, may he found in all
parts of the island. Among those may be mentioned a species of Mansonia,
probably Mansonia uniformis, which is present in certain localities. Towards
the centre and north of the Island nearly every pool of water containing
weed or alge is found to harbour numerous larvæ of Culex tænorhynchus often
in association with enormous numbers of the larvæ of N. rossi.
Section 4.
181. THE NATURAL ENEMIES OF MOSQUITOES.—It has long
been known that the number of mosquitoes may be largely reduced by the attacks
of natural enemies. The adult insects often fall a prey to birds, bats and
predacious insects and certain species of fish also attack and devour large
numbers when they approach sufficiently near the surface of the water. Two
species of fish, Haplochilus lineatus and Anabas scandens, occurring in streams,
pools and tanks in the neighbourhood of Bombay, readily take flying mosquitoes
in this way, leaping six inches or more out of the water for the purpose.
182. Ants will also attack and devour adult mosquitoes if they happen to
be in an enclosed space. This fact was demonstrated accidently during the present
investigation. A number of adult anopheles, which had been fed experimentally
upon cases of malaria, were placed in a large wooden box containing a vessel of
water until ready for dissection. Unfortunately a largo number of small red
ants obtained access to the box and devoured nearly every mosquito, attacking
even those that had settled on the surface of the water for the purpose of
depositing their eggs.
183. But though a large number of adult mosquitoes ara being constantly
destroyed by natural enemies, it is probable that this loss is small compared to
that occasioned by the natural enemies which pray upon the insect in its larval
state ; and the examination of collections of water containing mosquito larvæ
usually shows the presence of other aquatic larvæ and insects which help to
reduce their number very greatly. Mention has already been made in the
paragraph referring to Culex concolor and Culex tigripes of cannibal mosquito
larvæ present in Bombay, but in addition to these cannibal larvæ many other
natural enemies of mosquito have been met with during the examination of
collections of water on the island.
184. Among these a species of water boatmen, belonging to the Notonectidœ,
is especially common. This aquatic insect may easily be recognized by the fact
that it swims on its back. If carefully watched it may be seen to catch and
devour numbers of mosquito larvæ both Culicine and Anopheline. A miaute
water bug which kills anopheles larvæ has also been found in a large number of
wells and pools of water infested with mosquito larvæ. This bug, which is of a
dark grey or black colour, is only a fraction of an inch in length. It possesses a
long suctorial proboscis which is usually carried bent baneath its body. It runs
about rapidly on the surface of the water and attacks anopheles larvæ readily.
It may be seen to climb upon them at the tail end as they rest quiet on the
surface of the water ; then it moves cautiously forward as fat as the thorax of
the larva and inserting its proboscis sucks out the juice of its prey. One
small bug about as big as a pin's head has destroyed as many as ten anopheles
larvæ in the course of a few hours in the manner described.
185. Certain aquatic beetles belonging to the Dytiscidæ and Hydroplulidæ
are common in Bombay and their larvæ destroy considerable number of mosquita
larvæ. Many of these beetle larvæ have been found in the large shallow pools
of water common in the centre and north of the island. They vary in size
from 1/2" to 1" or more, possess a whitish, fleshy, somewhat maggot-shapad
body, and are provided with three pairs of legs and powerful jaws, The jaws
are peculiar, being adapted both for seizing and crushing their prey, and owing
to the fact that they are hollow, or groved, serve the purpose of a suctorial
apparatus also, by means of which the juices of the victim are rapidly absorbed.