67 
Hoiv Mosquitoes pass the Winter . 
“ The climate,” he says, “ is fairly cold in the winter, falling 
as low as 55° F. in the house at mid-day at times. Up to 
the end of October, perfect A. Bossii and A. Sinensis , sub-sp. 
nigerrimus, are common, but by November 20 had quite dis¬ 
appeared, nigerrimus being the species most in evidence while 
they were becoming more and more scarce. It is noteworthy 
that a very large proportion of these last visitors were $’s. 
I sought in every corner and could nowhere find a single 
hibernating specimen. 
“ On the other hand, Anopheles larvae persist in large numbers 
in certain tanks in the open, where the water is warmed by the 
sun all day long, but such pools are necessarily rare, as unless 
they are so placed as to be fed with fresh water or are exception¬ 
ally deep they must dry up. There is a small cemented tank in 
my garden which I keep replenished for observation, and which 
still has numbers of larvae, but usually no pupae. However, the 
margin of temperature inimical to pupation must be a very 
narrow one, as, after a fall of rain, accompanied by cloudy nights, 
during which the night temperature could not fall to the usual 
minimum, the higher temperature sufficed to bring about the 
appearance of a few pupae. Now the rain had not perceptibly 
altered the depth of the tank, which indeed is filled periodically 
from the well, and so fluctuates much more from this than it 
could do from any shower, so that the occurrence has evidently 
no connection with the rain per se. 
“ These facts, I think, point to the conclusion that one of the 
plans whereby our local Anopheles secure the maintenance of the 
species through periods untenable to the imagines is by the 
persistence of larvae which are capable of surviving as such, but 
t 
cannot pupate till the water grows warmer.” 
Further on in his letter he says that in the intense heat the 
Anopheles are rare, and supposes that they hide in sheltered 
places, as the larvae can then only be found in “ specially 
situated pools when the water is cool.” 
We find that in Culex hibernation takes place just as in 
Anopheles. Cellars form a favourite place for O. pipiens to pass 
the winter. In one case they are recorded by Westwood as 
coming out in the winter in a house and causing annoyance,* but 
such is unusual; they hibernated, he supposed, in a chimney. 
Wade and others observed this hibernation of Culex ; whilst in 
recent years more evidence regarding this point has come to 
* Proc. Ent. Soc. London, vii. 1876, and p. xxi. 1872. 
