IO4 ENTOMOLOGY 



The well-known " shrilling " of the male cicada is produced 

 by the rapid vibration of a pair of membranes, or drums, sit- 

 uated on the basal abdominal segment, and vibrated each by 

 means of a- special muscle. 



Frictional sounds are made by beetles in a great variety of 

 ways : by the rubbing of the pronotum against the mesonotum 

 (many Cerambycidge) ; or of abdominal ridges against elytral 

 rasps (Elaphrus, Cychrus) ; or two dorsal abdominal rasps 

 against specialized portions of the wing folds (Passalus cor- 

 nutus), not to mention other methods. In most cases one 

 part forms a rasp and the other a scraper, for the production 

 of sound. 



In many of these instances the sound serves to bring the 

 two sexes together and is not necessarily confined to one sex; 

 thus, in Passalus cornutus both sexes stridulate. 



A few moths (Sphingidae) and a few butterflies make 

 sounds ; the South American butterfly Ageronia feronia emits 

 a sharp crackling noise as it flies. A rasp and a scraper have 

 been found in several ants, though ants very seldom make any 

 sounds that can be distinguished by the human ear; Mutilla, 

 however, makes a distinct squeaking sound by means of a 

 stridulating organ similar to those of ants. 



Stridulating organs attain their best development in Orthop- 

 tera, in which group the ability to stridulate is often restricted 

 to the male, though not so often as is commonly supposed. 

 Among Acridiidse, Stenobothrus rubs the hind femora against 

 the tegmina to make a sound, the femur bearing a series of 

 teeth, which scrape across the elevated veins of the wing-cover ; 

 while the male of Dissosteira makes a crackling sound during 

 flight or while poising, by means of friction between the front 

 and hind wings, where the two overlap. 



Locustidse and Gryllidse stridulate by rubbing the bases of 

 the tegmina against each other. Thus in the male Microcen- 

 tnim laurifolium the left tegmen, which overlaps the right, 

 bears a file-like organ of about fifty-five teeth (Fig. 136) , while 

 the opposite tegmen bears a scraper, at right angles to the file. 



