120 THE SCIENTIFIC ANGLER. 



When insects arrive at maturity, there is this signal 

 and distinctive difference between the aerial and aquatic 

 species. The former are voracious feeders when in their 

 perfect state ; the latter do not, as we have shown, feed 

 at all when in the sub-imago and perfect stages of their 

 existence, so that no devastating results issue from any 

 multiplication of these. The same observation cannot 

 be applied with equal truth to the case of the land in- 

 sects, which, when plentiful, are the bane of man and 

 beast. Ecaumur makes mention of a swarm of May 

 flies or drakes on the Marne, which completely covered 

 him two or three inches in depth, in the space of a few 

 minutes. Most fishermen have experienced something 

 similar, at long intervals, with regard to the water flies 

 in certain localities: this is the result of a combination of 

 circumstances favorable to them. Seasonable weather is 

 always favorable to insect life. A mild winter will tend 

 to destroy the ensuing season's general supply, by caus- 

 ing premature activity, followed often by premature 

 death, or at best by a relapse into a state of torpor. 

 These changes invariably prove prejudicial to the exist- 

 ence of insects. Steady and severe cold, when season- 

 able, upon the other hand, is not only favorable to 

 insect life, by causing a continued state of torpor, from 

 which they emerge in due season, but also by indirectly 

 preserving them from the attacks of their numerous 

 enemies. It sometimes happens that, from a variety of 

 causes, running water is of a higher temperature than 

 the atmosphere, in dry frosty weather ; and as the aquatic 

 insect, prior to leaving its native element, is wholly in- 

 fluenced by it, an uprising of them when the air is too 

 cold for them to live in it, is not by any means an infre- 

 quent occurrence. We have observed them rise to live 

 but a few hours, and sometimes only minutes, in the 

 event of there being no sun temporarily to counteract 

 the effects of the keen air. 



