108 A BOOK OF INSECTS 



species, there is reason for thinking that no insect can see 

 an object at a greater distance than six feet. 



The fact that many insects are able to make audible 

 sounds lends strong support to the assumption that they 

 can hear, quite apart from the evidence of the specialised 

 ear-structures which many species possess. These sounds 

 are instrumental rather than vocal, most of them being 

 produced by the vibration of a membrane, or by the 

 friction of one part of the body against another part, the 

 process in the latter case being termed " stridulation." 

 Stridulating organs are possessed by many beetles, by 

 several ants, and by a few moths, but, as might be ex- 

 pected, they attain their greatest perfection among those 

 families of the Orthoptera which possess well-developed 

 ears. The so-called "song'' of the male cicada is pro- 

 duced by the rapid vibration of two membranes, or drums, 

 situated at the base of the abdomen, each drum being 

 worked by a special muscle. The wings of many 

 Hymenoptera and Diptera vibrate with so much speed 

 and regularity that a definite note is produced. This 

 wing tone, in the case of a hive-bee in vigorous flight, 

 is a in the treble clef, while it may drop to e if the insect 

 is fatigued or heavily laden. But the buzzing or humming 

 of insects is by no means always due to the vibration of 

 the wings. Flies, bees, dragon-flies, and some beetles are 

 able to produce at will a similar sound by means of vibra- 

 tile membranes situated just within the spiracles. All 

 bee-keepers are aware that the emotions of the hive find 

 expression in the sounds made by its inmates, while 

 some have ascribed a wide range of meaning to the 

 various notes which are produced. Thus, Mr. T. W. 

 Cowan, quoting from Stahala, says that " if in winter one 

 taps the hive and a loud ' Huumm ' is heard, it is a sign 

 that the bees have their queen and sufficient food. The 



