DESTRUCTIVE INSECTS. 17 



orchards and forests of New England were overrun by this worm, 

 and the leaves of the apple, oak and other trees devoured by it. 

 In 1853 the trees everywhere assumed a brown withered appear- 

 ance under their destructive attacks, looking as though they had 

 been scorched by fire. On jarring or shaking a tree hundreds 

 would instantly let themselves down from among the leaves, by 

 fine threads like cobweb, some dropping to the ground, others 

 remaining suspended in the air. They continued in full force 

 until 23rd June, when rain accompanied by heavy thunder caused 

 them to disappear. ^) 



19. The Aphis tribe, of which many species were so abundant 

 and destructive in the neighbourhood of Toronto during the dry 

 summer of 1856, is in some countries a most dreaded and de- 

 vastating pest. So wonderfully productive are the green plant 

 lice that in five generations one aphis may be the progenitor of 

 5,904,900,000 descendants; and it is supposed that in one year 

 there may be 20 generations (Reaumer). In 1810 the Pea crop 

 was almost entirely destroyed throughout Great Britain by an 

 aphis. Indeed next to the locust the aphidse may be said to be 

 the greatest enemies of the vegetable world (Kirby) . The won- 

 derful fertility of this tribe of insects exceeds that of any known 

 species, and elevates them to a position in the scale of pests and 

 plagues which secures for them the second, if not in many tem- 

 perate climates, the first place among insect depredators. A few 

 weeks is sufficient to convert a handful of these viviparous and 

 oviparous insects into countless legions, which taking flight, darken 

 the air by their numbers. In 1834 a great flight of these insects 

 was distributed by a strong wind over Belgium. In 1836 the 

 inhabitants of Hull, England, were seriously incommoded by 

 a host of them loading the air in numbers so immense as 



(1) See 2nd Report by Dr. Pitch. 



