HYBERNATION OF INSECTS. 



371 



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 de- 

 gree 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 marmots and dormice 

 thus treated ; and the Aphis of the rose (A. JRosce), which 

 becomes torpid in winter in the open air 1 , retains its activity, 

 and gives birth to a numerous progeny, upon rose trees pre- 

 served in greenhouses and warm apartments. 



But can we, in the same way, regard mere cold as the 

 cause of the hybernation of insects ? Is it wholly owing to 

 this agent, as most writers seem to think — to feelings either 

 of a pleasurable or painful nature produced by it — that, 

 previously to becoming torpid, they select or fabricate com- 

 modious retreats precisely adapted to the constitution and 

 wants of different species, in which they quietly wait the ac- 

 cession of torpidity and pass the winter ? In my opinion, 

 certainly not. 



In the first place, if sensations proceeding from cold lead 

 insects to select retreats for hybernating, how comes it that, 

 as above shown, a large proportion of them enter these retreats 

 before any severe cold has been felt, and on days considerably 

 warmer than many that preceded them ? If this supposition 

 have any meaning, it must imply that insects are so consti- 

 tuted that, when a certain degree of cold has been felt by 

 them, the sensations which this feeling excites impel them to 

 seek out hybernacula. Now the thermometer in the shade 

 on the 14th of October, 1816, when I observed vast numbers 

 thus employed, was at 58° : — this, then, on the theory in 

 question, is a temperature sufficiently low to induce the 

 requisite sensations. But it so happens, as I learn from my 

 meteorological journal (which registers the greatest and least 

 daily temperature as indicated by a Six's thermometer), that 

 on the 31st of August, 1816, the greatest heat was not more 

 than 52°, or six degrees lower than on the 14th of October : 

 yet it was six weeks later that insects retired for the winter ! 



1 Kyber, in Germar's Mag. der Ent. ii. 3. 

 B B 2 



