IMPERFECT SOCIETIES OF INSECTS. 11 



over a field of four acres as they passed. — Professor 

 Walch states, that one night about eleven o'clock, sitting 

 in his study, his attention was attracted by what seemed 

 the pelting of hail against his window, which surprising 

 him by its long continuance, he opened the window, and 

 found the noise was occasioned by a flight of the froth 

 frog-hopper [Cercopis spimiaria), which entered the room 

 in such nvmibers as to cover the table. From this cir- 

 cumstance and the continuance of the pelting, which 

 lasted at least half an hour, an idea may be formed of 

 the vast host of this insect passing over. It passed from 

 east to west ; and as his window faced the south, they 

 only glanced against it obliquely^. He afterwards wit- 

 nessed, in August, a similar emigration of myriads of a 

 kind of ground-beetle {Amaru vulgaris,)^. — Another 

 writer in the same work, H. Kapp, observed on a calm 

 sunny day a prodigious flight of the noxious cabbage- 

 butterfly [Pontia Brassica), which passed from north- 

 east to south-west, and lasted two hours'^. Kahn saw 

 these last insects midway in the British Channel**. Lind- 

 ley, a writer in the Royal Military Chronicle, tells us, 

 that in Brazil, in the beginning of March 1803, for many 

 days successively there was an immense flight of white 

 and yellow butterflies, probably of the same tribe as the 

 cabbage-butterfly. They were observed never to settle, 

 but proceeded in a direction from north-west to south- 

 east. No buildings seemed to stop them from steadily 

 pursuing their course ; which being to the ocean, at only 

 a small distance, they must consequently perish. It is 

 remarked that at this time no other kind of butterfly is 



* Naturforsch. vi. 111. '^ Ibid. xi. 95. 



" Ibid. 94. " Travels, i. 13. 



