Sensory Discrimination : Hearing 1 1 1 



36. Hearing in Insects 



The sense of hearing in insects also is problematical. 

 When the insect makes a sound itself, which, as in the case of 

 crickets, is connected with the mating process, it would seem 

 a priori highly probable that it can hear. Various structures 

 have been designated as auditory organs, the finely branched 

 antennae of mosquitos and gnats, on the same doubtful 

 evidence that they have been found to vibrate in response to 

 musical tones (264) ; and in the Orthoptera certain very 

 peculiar structures situated on the front legs of grasshoppers 

 and crickets, and in the first segment of the abdomen in 

 locusts. These structures Graber called chordotonal organs, 

 and he felt convinced from experimental tests that they 

 were auditory. The cockroach, Blatta, while running about 

 the room will stop, he says, for an instant when the strings of 

 a violin are struck. A blinded specimen, hung by a thread, 

 became violently agitated at a sudden tone from a violin. 

 A water insect, Corixa, although undisturbed by the water 

 vibrations produced by pushing a bone disk toward it in the 

 water, gave decided reactions when the disk was connected 

 with an electric bell. Other water beetles were still more 

 sensitive. That they distinguished pitch differences Graber 

 thought probable from the fact that he observed reactions 

 of different degrees of violence to sounds of different pitch; 

 and their discrimination of intensity changes he thought 

 demonstrated by the fact that if a continuous tone, sounding 

 while a water beetle is swimming about, be made suddenly 

 louder, the speed of the insect's movements visibly increases. 

 It is going rather far, however, to pass from the evidence that 

 insects discriminate sounds made by their own species from 

 other sounds to the conclusion that "they like us have the 

 capacity to analyze, at least to a certain degree, these 



