10 



IMPERFECT SOCIETIES OF INSECTS. 



lagers, under the idea that they were locusts 1 ; several 

 instances are given by Rosel of similar clouds of these in- 

 sects having been seen in Silesia and other districts 2 ; and 

 Mr. Woolnough of Hollesley in Suffolk, a most attentive 

 observer of nature, once witnessed such an army of the 

 smaller dragon-flies (Agrion) flying inland from the sea as to 

 cast a slight shadow over a field of four acres as they passed. 

 A migration of dragon-flies was witnessed at Weimar in 

 Germany in 1816, and one far more considerable, perhaps 

 the greatest on record, May 30th and 31st, 1839, when 

 cloud-like swarms of these insects (chiefly L. depressd) were 

 seen at Weimar, Eisenach, Leipsig, Halle, and Gottingen, 

 and the intervening country, extending over a very large 

 district. 3 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 (Aphrophora spumaria), which entered 

 the room in such numbers as to cover the table. From this 

 circumstance, 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. 4 He afterwards witnessed, in August, a similar 

 emigration of myriads of a kind of ground beetle (Amara 

 vulgaris). 5 But the most remarkable migrations of beetles are 

 those recorded by M. Lacordaire, who informs us that for two 

 successive years, when he was at Buenos Ayres, that city was 

 for about eight days in the spring of each year inundated by such 

 millions of Harpalus cupripennis, which arrived daily towards 

 nightfall, that it was necessary every morning to sweep them 

 from the exterior of the houses to a height of several feet 

 above the ground. 6 Another writer in the Naturf or seller, 

 H. Kapp, observed on a calm sunny day a prodigious flight of 



1 Naturforsch. vi. 110. 2 ii. 135. 



3 Weissenborn in Mag. Nat. Hist. N. S. iii. 516. 



4 Naturforsch. vi. 111. 5 Ibid. xi. 95. 

 c Lacordaire, Tntrod. a VEntom. ii. 494. 



