MEANS OF DEFENCE OF INSECTS. 409 



a defensive armour to them. Madame Merian has figured an enormous 

 caterpillar of this kind, which unfortunately she could not trace to the 

 perfect insect, by the very touch of which her hands, she says, were in- 

 flamed, and that the inflammation was succeeded by the most excruciating 

 pain. 1 The vesicatory beetles, likewise (Cantharis vesicatoria, &c.), are not 

 improbably defended from their assailants by the remarkable quality, so 

 useful to suffering mortals, that distinguishes them. 



Your own observation must have proved to you, that insects 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 remarkable instance of this is afforded by the com- 

 mon 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 2 , 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 anything animated or rendering them 

 distasteful to creatures that would otherwise prey upon them. The same 

 remark may apply to the slimy caterpillars of some of the saw-flies (Selan- 

 dria Cerasil Allantus Scropkularice, &c.). The coat of slime of these ani- 

 mals, as Professor Peck observes 3 , retains its humidity though exposed to 

 the fiercest sun. Under this head I shall also mention the phosphoric in- 

 sects : the glow-worm (Lampyris) ; the lantern-fly (Fulgora) ; the fire-fly 

 (Elater) ; and the electric centipede (Geophilus electricus) ; since the light 

 emitted by these animals may defend them from the attack of some 

 enemies. Mr. Sheppard once noticed a Carabus running round the last- 

 mentioned insect, when shining, as if wishing, but afraid to attack it. 



Various insects, doubtless, find the wonderful vitality* with which they 



Insect Surinam, t. 57. Two different specie's of caterpillars apparently related 

 to this of Madame Merian were in the late Mr. Francillon's cabinet, and are now in 

 my possession. 



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



5 Nat. Hist, of the Slug-worm, 7. 



4 The penetrating genius of Lord Verulam discovered in a great degree the causes 

 of this vitality. " They stirre," says he, speaking of insects, " a good while after 

 their heads are off, or that they be cut in pieces ; which is caused also for that their 

 vital spirits are more diffused thorowout all their parts, and lesse confined to organs 

 than in perfect creatures." Sylv. Sylvdr. cent. vii. 697. 



