HYBERNATION OF INSECTS. 527 



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

 injured. ^ 



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

 which states the consistency of the animal is almost as fluid as in 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 181 3-14 was one of the severest we had had for many years, 

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

 wlien 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 un- 

 injured ; 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 

 corresponding fact recorded, with surprise, by Boerhaave, that insects 

 abounded as much after the intense winter of 1709, during which Fahren- 

 heit's thermometer fell to 0°, as after the mildest season, we may see the 

 fallacy of the popular notion, that hard winters are destructive to insects. - 



But though many larvas 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 vid- 

 gnris) 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 no- 

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

 when dropped into a glass they chinked like stones, which nevertheless 

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

 found that when the larvae of Cnethocampa Pityocamj)a were frozen into 

 ice 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 observa- 

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

 valuable Essay on the Grub (larva of Tipula oleraceci) — 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 Brassicce, 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 caterpillars 

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



1 Tracts, 22. 



2 Vid. Spence in Transactions of the Hortkidt. Soc. of London, ii. 148. Compare 

 Deaum. ii. 141. 



3 Lister, Goedart, De Itisectis, 76. 



4 Reaum. ii. 142. 6 (Euvres, vi. 12. 



