312 OUR HOUSEHOLD INSECTS 



instances as well, and are such as might readily be 

 admitted in the present case, if it could be shown that 

 the insect possesses the requisite mechanism. But it is 

 just here that the difficulties come in : the extremely 

 minute size of the insect itself, and the softness of its 

 body, seem to be sufficient reasons to preclude the possi- 

 bility of its being the author of such ticking sounds. 

 The death-watch beetle is covered with an extremely 

 hard integument, and is, moreover, not very minute, 

 being about a quarter of an inch long ; and it is easy to 

 understand how blows given by its hard head against 

 timber are sufficiently violent to be audible as repeated 

 taps or ticks. But such is by no means the case with 

 the book-louse, and it is difficult to understand how an 

 insect so soft as to be crushed to death by the slightest 

 pressure, and so minute as to require a lens for the 

 purpose of observing even its true form, can by any 

 mechanical means at its disposal produce a sound loud 

 enough to be audible at all, much less at a distance. It 

 is true that the jaws are the hardest part of the body, 

 and these, it is said, are the parts by which the noise 

 is made ; nevertheless, one would suppose that the im- 

 pact of such minute specks upon any substance whatever 

 would, except under the most favourable conditions, be 

 quite inadequate for the production of any sound that 

 would be audible without the aid of a microphone. 



However, Derharn was very positive in his statements, 

 and since his time several other observers have recorded 

 somewhat similar experiences, from which we may quote 

 the following as perhaps the most circumstantial and 

 apparently convincing. It is a record by Mr. J. Black- 

 wall in the Entomologist's Monthly Magazine for 1867 : 

 " A ticking sound, so precisely similar to that of a watch 

 as scarcely to be distinguished from it by the nicest 



