DISEASES OF INSECTS. 209 



subject to vertigo, which has been attributed to their 

 eating poisonous honey a but may not this disease in all 

 these cases arise from some derangement of the nervous 

 system ? One of the ants which was so affected had lost 

 one of its antennae ; but as this was not the case with the 

 others, no great stress is to be laid upon the circumstance. 

 Huber does not inform us whether those attacked by 

 this disease recovered or not. 



I have observed more than once, that the fash-fly and 

 some others of the same tribe are subject in particular 

 seasons to a kind of convulsions. When thus attacked, 

 they kick and struggle, and seem unable to fly. Some- 

 times they lie upon their backs without motion, but if a 

 finger be placed near them their convulsive motions are 

 renewed. When thrown into the air, instead of flying, 

 they fall to the ground. Had this distemper occurred ear- 

 lier or later in the year I should have attributed it to the 

 benumbing effects of cold ; but as my observations were 

 made one year (1816) in May, and in another (1811) in 

 the latter end of June, this could scarcely be the case. 

 In the year last mentioned I observed that many flies 

 died under its influence. In wet seasons this tribe is 

 subject to another disease, which proves fatal to many of 

 them, and indeed to other Diptera. A white crust ap- 

 pears to be formed upon the abdomen both above and 

 below, of a granular appearance, much resembling fine 

 moist sugar. On the back of that part this crust does 

 not cover the margins of the segments, which gives it 

 the appearance of white bands ; so that deceived by it, I 

 have often at first flattered myself that I had met with 



a N. Diet. d'Hist. Nat. i. 42. 

 VOL. IV. P 



