514 PRODUCTION OF SOUNDS BY INSECTS. 



676. Many Insects have the power of prodacing a conti- 

 nuous sound, which probably serves the purpose of intimating 

 to each other the neighbourhood of their own kind ; and 

 even, in some instances, of expressing their feelings : some 

 of these sounds are produced only during flight. Of this 

 kind is the sharp hum of the Gnat, Mosquito, Gad-fly, &c., 

 which, though often a source of extreme annoyance to man 

 and beast, serves to give warning of the proximity of these 

 blood-thirsty Insects, and is therefore of real service to the 

 animals they attack. From recent experiments, however, it 

 appears that in Bees and Flies, at least, the sound is not 

 produced so much by the vibrations of the wings (to which it 



is commonly attributed), as 

 by those of a little mem- 

 branous plate, situated in 

 one of the spiracles or stig- 

 mata ( 321) of the thorax; 

 for if the apertures of these 

 be stopped, no sound is heard, 

 though the wings remain in 

 movement. But in Cock- 

 chafers, and other noisy 

 Beetles, Butterflies, &c., no 

 such apparatus can be dis- 

 Fig. 256.-BoMBYi.ius. covered. Other sounds are 



produced while the insect is feeding ; that occasioned by the 

 armies of Locusts, when incalculable millions of powerful jaws 

 are in action at the same time, has been compared to the crack- 

 ling of a flame of fire driven by the wind. Certain two-winged 

 Flies, distinguished by a long proboscis (fig. 256), make a 

 humming sound whilst sucking honey from flowers ; and the 

 same is the case with some of the Hawk-moths. 



677. Some Insects are remarkable for a peculiar mode of 

 calling, commanding, or giving an alarm. The neuters or 

 soldiers among the White Ants make a vibrating sound, 

 rather shriller and quicker than the ticking of a watch, by 

 striking against hard substances with their mandibles ; this 

 seems intended to keep the labourers, who answer it by a 

 hiss, upon the alert and at their work. The well-known 

 sound termed the "death-watch" is produced by a small beetle 

 termed Anobium (fig. 257), that burrows in old timber ; and 



