73
prevent ants from gaining access to tables, food-safes, etc., and they have also not
unfrequently been found in large numbers in wells, garden-tubs, stable-tubs, etc.
During the monsoon when countless small collections of water occur in flower
pots, broken bottles, tins and hollows in trees and many other places they
become exceedingly numerous. The most common species are Stegomia
scutellaris, Stegomia fasciata (the carrier of Yellow fever in the West Indies),
and Stegomyia sugens, and these three species may be met with in all parts of
the Island. They are specially common in A. Ward where there are numerous
offices and buildings containing fire buckets filled with water and in D. Ward
especially on Malabár Hill where many bungalows with large gardens exist.
177. Culeco concolor and Culex tigripes.—These two species of Culex which
resemble one another very closely, are very large mosquitoes ; they are very
common in many parts of Bombay ; and they usually breed in collections of
fairly clean water. Their larvæ are peculiar, because, unlike most culicine
larvæ, they float nearly horizontal in the water, in a position somewhat
resembling that adopted by anopheles larvæ. They attain a very large size
and they are cannibal in character, greedily devouring other mosquito larvæ
that may be sharing the same breeding-place with them and even feeding
upon one another. Their prevalence and relative distribution may be shown by
the fact that they were met with in 721 different breeding places during the
present enquiry. These breeding places were distributed as follows :—
A. Ward
B.
C.
D.
E.
F.
G.
..
45
44
.. 142
.. 186
.. 210
50
44
There is no evidence to show that Culex concolor and Culex tigripes are
harmful to man ; they do not appear to attack man very readily ; and in view of
the fact that they undoubtedly serve to reduce the numbers of other and possibly
dangerous species of mosquitoes they must be looked upon as being rather
beneficial than otherwise.
178. The larvæ of Culex concolor does not seek its prey, but waits for its
approach. It usually assumes an almost horizontal position just below the
surface of the water, admirably suited for attack upon larvæ of anopheles, which
float on the surface. Occasionally it may be seen to turn its body in a half circle,
when any moving object comes near it, as if it were keeping a sharp look-out
for the approach cf its prey. It is exceedingly voracious and when hungry will
seize any larva that ventures with striking distance, the movements of its head
and neck being so rapid that the eye cannot follow them. Small larvæ are
swallowed whole, disappearing instantaneously, large larvæ are seized and held
remorselessly in spite of their struggles, and rapidly devoured while still alive.
179. The following observation shows how destructive C. concolor may
be to other mosquitoes. Pour large larvæ of Culex concolor, when placed in a.
bowl containing a number of larvæ of Neocellia stephensi of different sizes,
immediately began to seize and devour them; and in the course of two hours
had destroyed over 50. It is interesting to note that breeding places which early
in the season contained large numbers of larvæ of Neocellia stephensi, and
which later in the year contained larvæ of Culex concolor also, were subse-
quently found to contain only the larvæ of Culex concolor. Unfortunately the
habit of preying upon one another in default of other mosquito larvæ tends to
limit their number, and though it is probable that they may effect some good in
areas where they are plentiful by destroying the larvæ of Neocellia stephensi,
there is no evidence to show to what extent this may take place.
180. Desvoidia obturbans.— Desvoidia obturbans (formerly called Culex
obturbans or Armigeres obturbans) is another species of mosquito present in
Bombay whose larvæ possess cannibal tendencies, but it is not so common as
Culex concolor, and as it usually breeds in foul water it rarely preys upon
B 136—19