94 INSECT MISCELLANIES. 



In the spirit of banter, Aristophanes makes Chae- 

 rephon ask Socrates whether gnats buz with their 

 mouth or their tail''\ Mouffet pronounces that the 

 sound comes from the mouth, because the sound is 

 louder when they approach than when they retire f. 

 *' After all," says Kirby, " the friction of the base of 

 the wings against the chest {thorax) seems to be the 

 sole cause of the alarming buz of the gnat, as well as 

 of the other two-winged flies {Dvpterci)^ This expla- 

 nation however seems not to accord well with Mr. 

 Kirby's additional remark, that gnats do not always 

 hum when they ily; for he ought to be prepared to 

 show that the wings do not rub on the thorax when 

 they are silent. " I have observed," says he, "that, early. 

 in the spring, before their thirst for blood seizes them, 

 gnats when flying emit no sound. At this moment 

 (February 18th) two females are flying about my 

 windows in perfect silence. The warmer the weather 

 the greater is their thirst for blood, the more forcible 

 their flight, the motion of their wings more rapid, 

 and the sound produced by that motion more intense. 

 In the night — but perhaps this may arise from the 

 universal stillness that then reigns — their hum ap- 

 pears louder than in the day : whence its tones may 

 seem modified by the will of the animal |." There 

 can be no doubt of the fact that gnats sometimes fly 

 in silence, however it may be explained : we have 

 observed that in a house where the hum of gnats 

 was not a little annoying in August, we could not 

 hear one in the end of September, though we 

 listened carefully to every individual which we saw 

 on the wing§. The "jarring hum" {asper^ ascerba 

 sonans)^ as Virgil expresses it, of the gad-fly is no 

 less annoying to cattle than that of the gnat and the 



* Nubes. t Theatrum Insectorum, 87. 



+ Intr. ii., 383. § J R 



