MEANS OF DEFENCE OF INSECTS. 927 
fore noticed’, are gifted, are doubtless a defensive ar- 
mour to them.—Madame Merian has figured an enor- 
mous 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 inflamed, and that the 
inflamination was succeeded by the most excruciating 
pain®, The vesicatory beetles, likewise, (Lytta vesica- 
toria, I’., &c.) are not improbably defended from their 
assailants by the remarkable quality, so useful to suffer- 
ing 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 (Lucanus pa- 
rallelopipedus, L..) 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 fo- 
rest-fly (Hippobosca equina, L.), which, as was before 
observed‘, can scarcely be killed by the utmost pressure 
of the finger and thumb. 
The znvoluntary secretions of these little beings may 
also be regarded as means of defence, which either con- 
* Vor. I. 4th Ed. p. 130, 131. 
b Insect. Surinam. t. 57. Two different species of caterpillars ap- 
parently related to this of Madame Merian were in the late Mr. 
Francillon’s cabinet, and are now in my possession. 
© Vor. I, 4th Ed. p. 148. 
02 
