340 On the Geographical Distribution of Insects. 



them through the medium of the plants which flourish dm-ing 

 the second, and acquire a sombre hue during the first, it may 

 be established as a general law, that throughout the globe the 

 march of insects is in intimate relation with that of vegeta- 

 tion. It is, moreover, probable that the dryness acts in a di- 

 rect manner on these animals, as it is known to do on the 

 caymans of America, which it throws into a real state of hy- 

 bernation, as has been shewn by M. de Humboldt, and as M. 

 Lacordaire has himself witnessed. 



It may be asked, if insects really perish dm-ing the dry sea- 

 son, or whether they only conceal themselves, as many of om's 

 do tlu-oughout the winter. Our author is of opinion that the 

 greater part perish, for they are seldom found under bark, in 

 the interior of the earth, or of vegetables, which might be ex- 

 pected if the case were otherwise. 



Another consideration, intimately connected Avith this, re- 

 lates to the form under which insects pass the winter in our 

 climates. All of them which appear in the spring must exist 

 in the beginning of winter, and necessarily pass that season 

 either in the state of egg, larva, pupa, or perfect insect. 



The species which come under the first category ai*e of 

 small amount compared to the entire mass of insects, which 

 is doubtless owing, on the one hand, to the circumstance, that 

 the greater part of young larvae, if disclosed in early spring, 

 would fail to find food ; and, on the other, to this, that the 

 substances in or upon which certain eggs must be deposited, 

 such as leaves or the larvae of other insects, do not exist at 

 that period. This refers chiefly to the kinds which produce 

 many generations in a yeai", and to such as undergo an incom- 

 plete metamorphosis, which do not attain their full develop- 

 ment till an advanced period of the year. In either case, the 

 eggs, being laid very late, cannot be hatched without the 

 yoimg larvae being exposed to the want of food, and it was 

 consequently n-jcessary that they should remain under that 

 form throughout the unfavourable season. It has been re- 

 marked as a singular fact in regard to the Lepidoptera, that 

 it is only such of them as have caterpillars which feed on pe- 

 rennial plants, that hybernate in the egg or larva state, while 

 those whose caterpillars live on annual plants do so under the 



