°630 HYBERNATION OF INSECTS. 
*bvious that something more than the sensation of heat is the regulator of 
the movements of each. Not, however, to detain you here unnecessarily, 
I shall not enlarge on this point, but shall pass on, in concluding this letter, 
“€o advert to the causes which have been assigned for the hybernation and 
torpidity of animals, and to state my own ideas on the subject, which will 
‘equally apply to the termination of this condition in spring. 
The authors who have treated on these phenomena have generally? re- 
‘ferred them to the operation of cold upon the animals in which they are 
“witnessed, but acting in a different manner. Some conceive that cold, com- 
‘bined with a degree of fatness arising from abundance of food in autumn, 
produces in them an agreeable sensation of drowsiness, such as we know, 
trom the experience of Sir Joseph Banks and Dr. Solander in Terra del 
‘Fuego, as well as from other facts, is felt by man when exposed to a very 
low temperature ; yielding to which, torpidity ensues. Others admitting 
that cold is the cause of torpidity, maintain that the sensations which 
precede it are of a painful nature ; and that the retreats in which hyber- 
nating animals pass the winter are selected in consequence of their endea- 
vours to escape from the disagreeable influence of cold. 
T have before had occasion to remark the inconclusiveness of many of 
the physiological speculations of yery eminent philosophers, arising from 
their ignorance of Entomology, which observation forcibly applies in the 
present instance. The reasoners upon torpidity have almost all confined 
their view to the hybernating quadrupeds, as the marmot, dormouse, &c., 
and have thus lost sight of the far more extensive series of facts supplied 
by hybernating insects, which would often at once have set aside their 
most confidently-asserted hypotheses. If those who adopt the former of 
the opinions above alluded to had been aware that numerous insects retire 
to their hybernacula (as has been before observed) on some of the finest 
days at the close of autumn, they could never have contended that this 
movement, in which insects display extraordinary activity, is caused by the 
agreeable drowsiness consequent on severe cold ; and the very same fact 
is equally conclusive against the theory that it is to escape the pain arising 
from a low temperature that insects bury themselves in their winter 
quarters. 
In fact, the great source of the confused and unsatisfactory reasoning 
which has obtained on this subject is, that no author, as far as my know- 
ledge extends, has kept steadily in view, or indeed has distinctly perceived, 
the difference between torpidity and hybernation ; or, in other words, 
between the stale in which animals pass the winter, and their selection of a 
situation in which they may become subject to that state. 
That the torpidity of insects, as well as of other hybernating animals, is, 
with us, caused by cold, is unquestionable. However early the period at 
which a beetle, for example, takes up its winter quarters, it does not suffer 
that cessation of the powers of active life which we understand by tor- 
pidity, until a certain degree of cold has been experienced ; the degree of its 
torpidity varies with the variations of temperature; and there can be no 
doubt that, if it were kept during winter from the influence of cold, it 
1 Here must be excepted my lamented friend the late Dr. Reeve of Norwich, 
who, in his ingenious Lssay on the Torpidity of Animals, has come to nearly the 
same conclusion as is adopted in this letter: but,'by omitting to make a distinction 
between torpidity and hybernation, he has not done justice to his own ideas, 
