564 HYBERNATION OF INSECTS. 



point, but shall pass on, in concluding this letter, to 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^ 

 referred them to the operation of cold upon the animals in which they 

 are witnessed, but acting in a different manner. Some conceive that cold, 

 combined with a degree of fatness arising from abundance of food in 

 autumn, produces in them an agreeable sensation of drowsiness, such as 

 we know, from 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 hybernating animals pass the winter are selected in conse- 

 quence of their endeavors to escape from the disagreeable influence of cold. 



I have before had occasion to remark the inconclusiveness of many of 

 the physiological speculations of very 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 them- 

 selves 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 per- 

 ceived, the difference between torpidity and hybernation ; or, in other 

 words, between the state 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 

 torpidity, 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 would not become torpid at all — at least this has proved the fact with 



' Here must be excepted my lamented friend llie late Dr. Reeve of Norwich, who, in his 

 ingenious Essay 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 hyber- 

 natiun, he has not done justice to his own ideas. 



