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LETTER XXYI. 



ON THE HYBERNATION OF INSECTS. 



If insects can boast of enjoying a greater variety of food than many other 

 tribes of animals, this advantage seems at first sight more than counter- 

 balanced in our climates by the temporary nature of their supply. The 

 graminivorous quadrupeds, with few exceptions, however scanty their bill 

 of fare, and their carnivorous brethren, as well as the whole race of birds 

 and fishes, can at all seasons satisfy, in greater or less abundance, their 

 demand for food. But to the great majority of insects, the earth for nearly 

 one half of the year is a barren desert, affording no appropriate nutriment. 

 As soon as winter has stripped the vegetable world of its foliage, the vast 

 hosts of insects that feed on the leaves of plants must necessarily fast 

 until the return of spring : and even the carnivorous tribes, such as the 

 predaceous beetles, parasitic Hipnenoptera, Sphecina, &c. would at that 

 period of the year in vain look for their accustomed prey. 



How is this difficulty provided for ? In what mode has the Universal 

 Parent secured an uninterrupted succession of generations in a class of 

 animals for the most part doomed to a six months' deprivation of the food 

 which they ordinarily devour with such voracity ? By a beautiful series of 

 provisions founded on the faculty, common also to some of the larger 

 animals, of passing the winter in a state of torpor — by ordaining that the 

 insect shall live through that period, either in an incomplete state of its 

 existence when its organs of nutrition are undeveloped, or, if the active 

 epoch of its life has commenced, that it shall seek out appropriate lu;- 

 bernacula, or winter quarters, and in them fall intoa.profound sleep, during 

 which a supply of food is equally unnecessary. 



In two of the four states of existence common to insects, in which 

 different tribes pass the winter, namelv, the egg and the pupa state, the 

 organs for taking food (except in some cases in the latter) are not de- 

 veloped, and consequently the animal is incapable of eating. The existence 

 of insects in these states during the winter difi'ers from their existence in 

 the same form in summer only in the greater length of its term. In both 

 seasons food is alike unnecessary, so that their hybernation in these cir- 

 cumstances has little or nothing analogous to that of larger animals. With 

 this, however, strictly accords their hybernation in the larva and imago 

 states, in which their abstinence from food is solely owing to the torpor 

 that pervades them, and the consequent non-expenditure of the vital 

 powers. — I shall attend to the peculiarities of their hybernation in each of 

 these states in the order just laid down ; premising that we have yet nuich 

 ■ to learn on this subject, no observations having been instituted respecting 

 the state in which multitudes of insects pass the winter. 



