456 HYBERNATION OF INSECTS: 
ward springs. Thus in the early spring of 1805 (to ig 
a memorable one, since in it I began my entomological 
career, and had anxiously watched its first approaches 
in order to study practically the science of which I had 
gained some theoretical knowledge in the winter, ) insects 
were generally out by the middle of March; and before 
the 30th, I find, on referring to my entomological jour- 
nal, that I had taken and investigated (I scarcely need add, 
not always with a correct result,) fifty-eight coleopterous 
species: while in the last untoward spring (1816) I did not 
observe even a bee abroad until the 20th of April ; and the 
first butterfly that I saw did not appear until the 26th. 
There are, however, circumstances connected with 
this reappearance, which seem to prove that something 
more than the mere sensation of warmth is concerned in 
causing it. I shall not insist upon the remarkable fact 
which Spallanzani has noticed, that insects reappear in 
spring at a temperature considerably lower than that at 
which they retired in autumn; because it may be plau- 
sibly enough explained by reference to their increased 
irritability in spring, the result of so long an abstinence 
from food, and their consequent augmented sensibility 
to the stimulus of heat. But ifthe mere perception of 
warmth were the sole cause of insects ceasing to hyber- 
nate, then we might fairly infer, that species of apparently 
similar organization, and placed in similar circumstances, 
would. leave their winter quarters at the same time. This, 
however, is far from being the case. Reaumur observed 
that the larvee of Papilio Cinzia quitted their nest a full 
month sooner than those of Bombyx chrysorrhea*. The 
reason is obvious; but cannot be referred to mere sen- 
@ Reaum. ii. 170. 
