252 MEANS OF DEFENCE OF INSECTS. 



that this altogether fabulous, since the animal has not 

 the power of moving them a . Their use is still unknown. 



Whether the long and often threatening horns on 

 the head, thorax, and even elytra, with which many in- 

 sects are armed, are beneficial to them in the view under 

 consideration, is very uncertain. They are frequently 

 sexual distinctions, and have a reference probably ra- 

 ther to sexual purposes and the economy of the animal, 

 than to any thing els<f. They may, however, in some 

 instances deter enemies from attacking them, and there- 

 fore it was right not to omit them wholly, though I shall 

 not further enlarge upon them. Their mandibles or 

 upper jaws, though principally intended for mastication, 

 and in the case of the Hymenoptera^ as instruments 

 for various economical and mechanical uses, are often 

 employed to annoy their enemies or assailants. I once 

 suffered considerable pain from the bite of the common 

 water-beetle (Dytiscus marginalis\ as well as from that 

 of the great rove-beetle (Goerius olens) ; but the most 

 tremendous and effectual weapon with which insects 

 are armed though this, except in the case of the scor- 

 pion, is also a sexual instrument, and useful to the fe- 

 males in oviposition is their sting. With this they 

 keep not only the larger animals, but even man himself, 

 in awe and at a distance. But on these I enlarged suf- 

 ficiently in a former letter 5 . 



These weapons, fearful as they are, would be of 



a DeGeer, i. 149- 



b Mr. MacLeay relates to me, from the communications of Mr. E. 

 Forster, the following particulars respecting the history of Mutilla 

 coccinca, which from this account appears to be one of the most re- 

 doubtable of stinging insects. The females are most plentiful in 

 Maryland in the months of July and August, but are never very 



