NOTES, CAPTURES, ETC. 189 



devouring ginger, rhubarb, cayenne pepper, &c, even perforating 

 tin -foil, in the larva state. They are very fond of biscuits ; I have 

 found them in profusion in an old tin that had been put by and 

 forgotten. The wood-feeders alone produce the sound, not 

 because of their structure, but because of the medium by which 

 they are surrounded, and it is probable that the power is by no 

 means confined to the two species, A. domesticum and X. tes- 

 selatum ; the others live in the open country, and will naturally 

 not be observed to produce the sound. The sound of the Death 

 Watch is certainly not vocal, as is suggested by Mr. Clifford 

 (Entom. xvii. 167); no insect produces a vocal sound, at any rate 

 one that is appreciable to human ears. Sir John Lubbock, noticing 

 the wonderful way in which ants communicated with each other, 

 made very delicate experiments with the sensitive flame and 

 microphone in order to ascertain if they communicated by sound, 

 but although with the latter instrument he could distinctly hear 

 the tread of their feet, the results were entirely negative. The 

 hum of bees, &c, is produced by the vibration of the wings; the 

 chirp of the cricket and Cicada and other insects by stridulation, 

 or the rubbing of one rough surface against another on some 

 part of the body; the so-called "squeak" of the Death's-head 

 moth is produced by the same cause ; several butterflies are 

 provided with a stridulating apparatus, and produce a very 

 distinct sound. The "tick" of the Anobium, then, is evidently 

 caused by some hard portion of the insect coming in contact with 

 the wood, either by the mandibles gnawing the wood or by the 

 head being rapped against it. If we adopt the former theory, 

 there is no need for further explanation. Professor Westwood, 

 from a series of observations made by him, is inclined to think 

 that the sound is produced by the larva as well as the perfect 

 insect, as they gnaw the wood while boring their burrows. If, 

 however, the sound is produced by the head being rapped against 

 the wood, this must be apparently done for one of two reasons : 

 either as a call from the insect to its mate, or in order to ascertain 

 the thickness of the wood which still remains unbored. The 

 sound is not one that would be produced by mandibles in gnawing, 

 but is a distinct sharp rapping sound, and would rather lead us 

 to adopt one of the latter explanations : the question, however, of 

 the real cause still remains to be decided. The reason why the 

 beetle has got its ominous appellation of the "Death Watch" is 



