182 



The Na.turalist. 



This brings ns to the question of the influence which atmospheric 

 changes have on insect life. Probably they have at times a greater 

 effect in keeping down excess than all other causes put together. 

 Insects are very susceptible to them. Let anyone go to the edge of a 

 wood well stocked with flowering plants, on a bright warm summer's 

 day ; what an abundance of insect life is to be seen ! If there is 

 water, all orders are represented — diptera especially, or most percep- 

 tibly abound ; but if a shower comes on, there is at once an apparent 

 scarcity, not a real one in this case. The insects have not gone, they 

 have only concealed themselves ; for if the shower ceases and the sun 

 shines again, they appear in even greater numbers than before, 

 eij joying the freshness produced by the rain. 



In discussing the causes of scarcity, it may be as well to mention in 

 this place a theory which has been broached, namely, that no species 

 of insect is absolutely scarce ; but that many are rare in collections, 

 or only apparently scarce, because we do not sufficiently know their 

 habits ; because we do not know where, or we do not know when, or 

 we do not know how, to find them. It is not my purpose to go into 

 this subject now, but I may have to touch somewhat near it. Later 

 on, if there is time, or on some other occasion, if desirable, I shall be 

 prepared to argue the question. 



Let us first inquire, what is the most critical period in the life of a 

 lepidopterous insect '? The answer will probably be, that' there are 

 two critical periods : the first immediately after its exclusion from the 

 egg, when it may be said to be in its infancy ; and the other when the 

 larva has arrived at its last moult, and is ready for change to the 

 pupal state. Now, what is likely to be the effect of pelting and 

 continuous rain on very young larvge 1 If a person goes into the woods 

 immediately after heavy rain, he sees numerous larvae which have 

 evidently been beaten down, and many are creeping up the trees ; but 

 such as he sees are mostly from half to full-grown, the very young 

 larvae will generally escape observation, and it can scarcely be doubted 

 that numbers must perish from inability to regain their food. On this 

 point, breeders of lepidoptera fail to give us all the information that is 

 needed, because they breed them under the most favourable circum- 

 stances they can, and do not as a rule expose them to the weather ; 

 even when they do, the larvae do not get the same beating down which 

 they are subjected to in the natural way of feeding. But breeders 

 know this fact, that if they feed larvae on wet leaves, those of most 

 species are liable to a disease which proves fatal to them, and this is 

 most evident when they are nearly full-grown. 



