238 ON INSECT SOUNDS. 



butterfly about nine times a second, also the day flying Lepidoptera, 



none of whom make any sound. But if the wing membrane be 

 very dry a fluttering or rustling sound is produced, notwithstanding 

 the slowness of movement as, e.g. in the dragon fly, the sound 

 being caused by contact of parts of one wing with the other. In 

 the families of Diptera and Hymenoptera, a wonderful variety of 

 sound produced by the motion of the wings is heard. The 

 rapidity of wing motion is due to excessive development of muscle 

 in the Thorax, and the wings cause sound in the same way as 

 tongues of metal do when made to vibrate. 



To determine the note of a free flying insect requires a very 

 musical ear, and also long practise in recognising and distinguishing 

 the note sounded by an insect flying rapidly by, as any body will 

 find who tries. Dr. Landois advises the observer to hum lightly 

 to himself the tone a', so as to catch the tone of a passing 

 insect, which he says can, with practise, be done. Thus we may 

 ascertain, for instance, the note of the common fly f, and the 

 honey bee a' The wing tone which each individual gives is nearly 

 constant ; but the size of the individuals of the same species 

 exercises some influence upon the pitch of the tone, which, 

 however, being of little moment, may be left out of consideration. 

 When the insect is very tired, it makes less rapid wing movements 

 and its note sinks. In the case of a bee which had been much 

 used up in experiments and was obviously exhausted, its natural 

 tone a' sank to e' a fourth below. 



When the sexes of the same species differ much in size, so does 

 the wing tone. Thus the small male of Bomb us terrestris has for 

 its note a', whilst its much bigger mate sings an octave deeper — 

 This depends of course on the size of the wing and the greater or 

 less rapidity of its movement. But there are small species of 

 insects which have a considerably deeper tone than some larger 

 species. The small Hoematopota pluvialis (a bee) gives the tone 

 h, whilst the much larger bee gives a tone more than an octave 

 higher. This depends on the number of wing vibrations in a 

 given time. 



