Ch. XLII.] 



AGENCY OF INSECTS. 



439 



'S, 



s 





. T. 



. * 



Df^. 







■\r 



.J 



tiis 



n 



05 



■ i 



.1, 



-« .-a 





m 



r. 



-J 



\^ 



I 



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1 



,.1 



P' 



flies of Ji". vomitoria could devonr a dead horse as quicldy as 

 a lion;^ and another Swedish naturalist remarks^ that so 

 great are the powers of propagation of a single species even 



commit 



more ravages than the elephant.f 



Next to locusts, the aphides, perhaps, exert the greatest 

 power over the vegetable world, and, like them, are sometimes 



numerous 



mu 



little creatures is without parallel, and almost every plant has 



^ 



its peculiar species. Eeaumur has proved that in five gene- 

 rations one aphis may be the progenitor of 5,904,900,000 

 descendants ; and it is supposed that in one year there may 

 be twenty generations.:!: Mr. Curtis observes that, as among 



some 



attached to one or more particular species of plants, and 

 others that feed indiscriminately on most sorts of herbage, so 

 it is precisely with the aphides : some are particular, others 

 more general feeders; aud as they resemble other insects in 

 this resi3ect, so they do also in being more abundant in some 

 years than in others. § In 1793 they were the chief, and in 

 1798 the sole, cause of the failure of the hops. In 1794, a 

 season almost unparalleled for drought, the hop was perfectly 

 free from them ; while peas and beans, especially the former. 



much from 



some of our smaller 



afford a good ilKistration of the temporary increase of a 

 species. The oak trees of a considerable wood have been 

 stripped of their leaves as bare as in winter, by the caterpillars 

 of a small green moth {Tortrix viridana)^ which has been ob- 

 served the year following not to abound. The silver 



Y moth 



common 



dreaded by us for its devastations ; but legions of their cater- 

 pillars have at times created alarm in France, as in 1735. 

 Eeaumur observes that the female moth lays about 400 eggs ; 

 so that if twenty caterpillars were distributed in a garden, and 



all lived 



through 



the winter and became moths in the 



May 



* Kirby and Spence, vol. i. p. 250. 

 j[ Wilcke, Amoei]. Acad. c. ii. 



I Kirby and Spence, vol. i. p. 174 

 Trans. Linn. Soc. vol. vi. 



