MEANS OF DEFENCE OF INSECTS. 



185 



their assailants by the remarkable quality, so useful to suffer- 

 ing mortals, that distinguishes them. 



Your own observation must have proved to you, that in- 

 sects often escape great perils, from the crush of the foot, or 

 of superincumbent weights, by the hardness of the substance 

 that covers great numbers of them. The elytra of many 

 beetles of the genus Hister are so nearly impenetrable, that it 

 is very difficult to make a pin pass through them ; and the 

 smaller stag-beetle (Dorcus parallelipipedus) will bear almost 

 any weight — the head and trunk forming a slight angle with 

 the abdomen — which passes over it upon the ground. Other 

 insects are protected by the toughness of their skin. A re- 

 markable instance of this is afforded by the common forest- 

 fly {Hippobosca equina), which, as was before observed, can 

 scarcely be killed by the utmost pressure of the finger and 

 thumb. 



The involuntary secretions of these little beings may also 

 be regarded as means of defence, which either conceal them 

 from their enemies, make them more difficult to be attacked, 

 or render them less palatable. Thus, the white froth often 

 observable upon rose-bushes, and other shrubs and plants, 

 called by the vulgar frog-spittle, — but which, if examined, 

 will be found to envelope the larva of a small hemipterous 

 insect {Aphrophora spumaria), from whose anus it exudes, 

 although it is sometimes discovered even in this concealment 

 by the indefatigable wasps, and becomes their prey, — serves 

 to protect the insect, which soon dies when exposed, not only 

 from the heat of the sun and from violent rains, but also to 

 hide it from the birds and its other foes. The cottony 

 secretion that transpires through the skin of Eriosoma 1 , and 

 some species of Coccus, and in which the eggs of the latter 

 are often involved, may perhaps be of use to them in this 

 view ; either concealing them — for they look rather like 

 little locks of cotton, or feathers, than any thing animated — 

 or rendering them distasteful to creatures that would other- 

 wise prey upon them. The same remark may apply to the 

 slimy caterpillars of some of the saw-flies (Selandria Cerasi, 



1 To this genus belongs the apple Aphis, called A. lanigera. 



