328 THE GREAT WATER-BEETLE. 



but, in truth, no insect that we know of has the 

 requisite organs to produce a genuine voice. They 

 emit sounds by other means, probably all external. 

 The grasshopper and the cricket race effect their 

 well-known and often wearisome chirpings by 

 grating their spiny thighs against their rigid wings ; 

 and this acherontia atropos appears to produce 

 the noise it at times makes, which reminds us of the 

 spring call of the rail or corncrake, by scratching 

 its mandible, or the instrument that it perforates 

 with, against its horny chest. The object of this 

 noise is, apparently, a mere sexual call. Heavy 

 and unwieldy creatures, they travel badly, and 

 from the same cause fly badly and with labour ; 

 and as they commonly hide themselves deep in the 

 foliage and obscurity, without some such signal of 

 their presence a meeting of the parties would seldom 

 be accomplished. 



Another of the ravenous creatures that infest 

 our pools is the great water-beetle (ditiscus mar- 

 ginalis) ; and perhaps it is the most ferocious of 

 any of them, being adapted by every provision 

 for a life of rapine, endued with great muscular 

 power, armed with a thick and horny case over 

 its body, and having its eyes large to observe all 

 the creatures about it, and powerful mandibles to 

 seize and reduce them to fragments. It riots, the 

 Polyphemus of the pool ; and having thinned its 

 herd in one place, is supplied with wings to effect 

 a removal to a fold better furnished. It even eats 

 the young of the frog ; and its bite is so powerful, 



