FLIES. 275 



Extraordinary swarm of flies. During the month 

 of September, in the year 1831, a small dipterous 

 insect, belonging to Meigen's genus Chlorops, and 

 nearly allied to, if not identical with, his C. Iceta, ap- 

 peared suddenly in such immense quantities in one 

 of the upper rooms of the Provost's Lodge, in King's 

 College, Cambridge, as almost to exceed belief. The 

 same species of fly, or one closely approaching to 

 it, is not uncommon in most houses towards the de- 

 cline of the summer ; but in this instance their 

 numbers were so great, and their appearance so 

 sudden, as to surpass anything of the kind I had 



Sporendonema musc<s of Fries ;* adding, that there was little doubt 

 that the fly is attacked by it while yet living, but that the para- 

 site is not fully developed till after death. The disease, it appears, 

 may occur at any time, where circumstances are favourable for 

 the growth of the fungus. The reason why it prevails most in the 

 autumn is the dampness of the air at that season, which promotes 

 the growth of all kinds of mould ; and the suddenness with which 

 the flies appear to be attacked is probably due to the rapid deve- 

 lopment of the fungus during the chill of an autumnal night. In 

 the case of flies which are found occasionally, at all seasons, stick- 

 ing to panes of glass, especially of windows that are not often 

 opened to keep up a free circulation of air, the cause of death is 

 the same, but it seems to come on more gradually. 



It was probably individuals labouring under this disease which 

 White saw, when (speaking of flies in houses in the decline of 

 the year) he says, ** at first they are very brisk and alert, but, 

 as they grow more torpid, one cannot help observing that they 

 move with difficulty, and are scarce able to lift their Iges, which 

 seem as if glued to the glass ; and by degrees many do actually 

 stick on till they die in the place." Nat. CaL p. 114. 



* See Eng. Flor. vol. v. pt. ii. p. 350. 



