HYBERNATION OF INSECTS. 561 



impaired. Others were exposed even to 56° below zero, without being 

 injured.^ 



A less degree of cold suffices to freeze many pupae and larvae, in both 

 which states the consistency of the animal is almost as fluid as that of 

 the egg. Their vitality enables them to resist it to a certain extent, and 

 it must be considerably below the freezing point to affect them. The 

 winter of 1813-14 was one of the severest we had had for many years, 

 Fahrenheit's thermometer having been more than once as low as 8° when 

 the ground was wholly free from snow ; yet almost the first objects which 

 I observed in my garden, in the commencement of spring, were numbers 

 of the caterpillars of the gooseberry-moth {Abraxas grossulariata) , which, 

 though they had passed the winter with no other shelter than the slightly 

 projecting rim of some large garden-pots, were alive and quite uninjured ; 

 and these and many other larvae never in my recollection were so numerous 

 and destructive as in that spring: whence, as well as from the correspond- 

 ing fact recorded, with surprise, by Boerhaave, that insects abounded as much 

 after the intense winter of 1709, during which Fahrenheit's thermometer 

 fell to 0°, as after the mildest season, we may see the fallacy of the pop- 

 ular notion, that hard winters are destructive to insects.^ 



But though many larvae and pupae are able to resist a great degree of 

 cold, when it increases to a certain extent, they yield to its intensity and 

 become solid masses of ice. In this state we should think it impossible 

 that they should ever revive. That an animal whose juices, muscles, and 

 whole body have been subjected to a process which splits bombshells, and 

 converted into an icy mass that may be snapped asunder like a piece of 

 glass, should ever recover its vital powers, seems at first view little less 

 than a miracle ; and, if the reviviscency of the wheel animal (Rotifer 

 vulgaris) and of snails, &,c., after years of desiccation, had not made us 

 familiar with similar prodigies, might have been pronounced impossible ; 

 and it is probable that many insects when thus frozen never do revive. 

 Of the fact, however, as to several species, there is no doubt. It was first 

 noticed by Lister, who relates that he had found caterpillars so frozen, 

 that when dropped into a glass they chinked like stones, which neverthe- 

 less revived.^ Reaumur, indeed, repeated this experiment without success ; 

 and found that when the larvae of Cnethocampa Pityocampa were frozen 

 into icB by a cold of 15° R. below zero (2° F. below zero), they could 

 not be made to revive.^ But other trials have fully confirmed Lister's 

 observations. My friend Mr. Stickney, before mentioned as the author of 

 a valuable Essay on the Grub (larva of TijjuJa oleracea) — to ascertain 

 the effect of cold in destroying this insect, exposed some of them to a 

 severe frost, which congealed them into perfect masses of ice. When 

 broken, their whole interior was found to be frozen. Yet several of these 

 resumed their active powers. Bonnet had precisely the same result with 

 the pupae of Pontia Brassiccc, which, by exposing to a frost of 14° R. 

 below zero (0° F.), became lumps of ice, and yet produced butterflies^; 

 and in an experiment made during Sir John Ross's voyage on the cater- 

 pillars of a moth (Laria Rossii) two of them revived, and one assumed 



> Tracts, 22. " 



* Vid. Spence in Transactions of the Horticult. Soc. of London, ii. 148. Compare Reaum. 

 ii. 141. 



* Lister, Goedart, De Insectis, 76. ■♦ Reaum. ii. 142. * CEuvres, vi. 12. 



