80 AN INTRODUCTION TO ENTOMOLOGY 



houses and in furniture, where they make a ticking sound by striking 

 their heads against the walls of their burrows. The sound consists of 

 several, sharp, distinct ticks, followed by an interval of silence, and is 

 believed to be a sexual call. 



The name death-watch was applied to these insects by supersti- 

 tious people who believed that it presaged the death of some person 

 in the house where it is heard. This belief probably arose from the 

 fact that the sound is most likely to be heard in the quiet of the night, 

 and would consequently be observed by watchers by sick-beds. 



The name death-watch has also been applied to some species of the 

 Psocidae, Clothilla pulsatoria and Atropos dimnatoria, which have been 

 believed to make a ticking sound. This, however, is doubted by 

 some writers, who urge that it is difficult to believe that such minute 

 and soft insects can produce sounds audible to human ears. 



The death-watches produce their sounds individually ; , but an 

 interesting example of an insect chorus is cited by Sharp ('99, p. 156), 

 who, quoting a Mr. Peal, states that an ant, presumably an Assamese 

 species, "makes a concerted noise loud enough to be heard by a human 

 being at twenty or thirty feet distance, the sound being produced by 

 each ant scraping the horny apex of the abdomen three times in rapid 

 succession on the dry, crisp leaves of which the nest is usually com- 

 posed." 



b. THE MUSIC OF FLIGHT 



The most obvious method by which insects produce sounds is by 

 beating the air with their wings during flight. It can be readily seen 

 that if the wing-strokes are sufficiently rapid and are uniform, they 

 will produce, like the flapping reeds of a mouth organ, a musical note. 



When, however, we take into account the fact that to produce the 

 lowest note regularly employed in music, the C of the lowest octave, 

 requires 32 vibrations a second, i. e,, nearly 2,000 vibrations per' 

 minute, it will seem marvellous that muscular action can be rapid 

 enough to produce musical notes. Nevertheless, it is a fact that 

 many insects sing in this way; and too their notes are not confined to 

 the lower octaves. For example, the common house fly hums F of 

 the middle octave, to produce which, it must vibrate its wings 345 

 times per second or 20,700 times per minute. 



As a rule, the note produced by the wings is constant in each 

 species of insect. Still with insects, as with us, the physical condition 

 of the singer has its influence. The vigorous honey-bee makes the A 

 of 435 vibrations, while the tired one hums on the E of 326 vibrations. 



