88 AN INTRODUCTION TO ENTOMOLOGY 



the dorsal wall of the segment bearing the file is made to vibrate 

 by the successive impacts of the scraper upon the ridges of the 

 file. In fact this seems to me more probable than that the 

 sound produced is merely that of the scraper striking against the 

 successive ridges of the file. There is at least one recorded case 

 where the body wall is specialized to act as a sounding board. 

 According to Sharp ('95, p. 200), in the males of the Pneumorides, 

 a tribe of South African Acridiidas, where the phonetic organ is 

 situated on the abdomen, this part is inflated and tense, no 

 doubt with the result of increasing the volume and quality of the 

 sound. 



Ordinarily the stridulating organs of insects are fitted to produce 

 notes of a single degree of pitch; but Gahan ('oo) figures those of 

 some beetles that are evidently fitted to produce sounds of more than 

 one degree of pitch; the file of Hispopria foveicollis, consists of three 

 parts, one very finely striated, followed by one in which the striae are 

 much coarser, and this in turn followed by one in which the striation 

 is intermediate in character between the other two. 



While the stridulating organs of the Orthoptera are possessed 

 almost exclusively by the males, in the Coleoptera, very many species 

 of which stridulate, the phonetic organs are very commonly possessed 

 by both sexes, and serve as a mutual call. In one genus of beetles, 

 Phonapate, stridulating organs have been found only in the females 

 (Gahan, 'oo). 



It seems evident that in the great majority of cases the sounds 

 produced by insects are sexual calls; but this is not always so. It 

 was pointed out long ago by Charles Darwin that " beetles stridulate 

 under various emotions, in the same manner as birds use their voices 

 for many purposes besides singing to their mates. The great Chiasog- 

 nathus stridulates in anger or defiance ; many species do the same from 

 distress or fear, if held so that they cannot escape; by striking the 

 hollow stems of trees in the Canary Islands, Messrs. Wollaston and 

 Crotch were able to discover the presence of beetles belonging to the 

 genus Acalles by their stridulation. Lastly the male Ateuchus 

 stridulates to encourage the female in her work and from distress 

 when she is removed" (The Descent of Man). 



The most remarkable case where stridulating organs have been 

 developed for other than sexual pusposes is that of the larvae of certain 

 Lucanidse and Scarabaeidae described by Schiodte ('74). In these 

 larvae there is a file on the coxa of each middle leg, and the hind legs 

 are shortened and modified so as to act as scrapers. The most highly 



