82 ENTOMOLOGY 



he flutters about in an aimless way and is no longer able to find the 

 female. 



Among beetles, males of Polyphylla gather and scratch at places where 

 females are about to emerge from the ground. Prionus also assembles, 

 as Mrs. Dimmock observed in Massachusetts. In this instance many 

 males, with palpitating antennas, ran and flew to the female; moreover, a 

 number of females were attracted to the scene. 



Sounds of Insects. Before considering the sense of hearing, some 

 account of the sounds of insects is desirable. Most of these are made by 

 the vibrations of a membrane or by the friction of one part against another. 



The wings of many Diptera and Hymenoptera vibrate with sufficient 

 speed and regularity to give a definite note. The wing tone of a honey 

 bee is A ' and that of a common house fly is F f . From the pitch the num- 

 ber of vibrations may be determined ; thus A ' means 440* vibrations per 

 second and F', 352. The numbers thus ascertained may be verified by 

 Marey's graphic method (Fig. 74) ; he found that the fly referred to ac- 

 tually made 330 strokes per second against the smoked surface of a re- 

 volving cylinder. 



Flies, bees, dragon flies and some beetles make buzzing or humming 

 sounds by means of the spiracles, there being behind each spiracle a mem- 

 brane or chitinous projection which vibrates during respiration. This 

 "voice" should be distinguished from the wing tone when both are pres- 

 ent, as in bees and flies. A fly will buzz when held by the wings, and some 

 gnats continue to buzz after losing wings, legs and head. The wing tone 

 is the more constant of the two; in the honey bee it is A f , falling to E' 

 if the insect is tired, while the spiracular tone of the same insect is at least 

 an octave higher (A ") and often rises to B" or C", according to the state of 

 the nervous system; in fact, it is possible and even probable that various 

 spiracular tones express different emotions, as is indicated by the effects 

 produced by the voice of the old queen bee upon the young queens and 

 the males. 



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

 rapid vibration of a pair of membranes, or drums, situated 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 Cerambyci- 

 dae); or of abdominal ridges against elytral rasps (Elaphrus, Cychrus)\ 

 or two dorsal abdominal rasps against specialized portions of the wing 



1 Upon the basis of C' as 264 vibrations per second. The C' of the physicist has 256 as its 

 frequency of vibration. 



