MEANS OF DEFENCE OF INSECTS. 207 



relates to me that he once saw this animal use them to rid 

 itself of a mite that incommoded it. They are probably 

 equally useful in delivering it from the ichneumon and its 

 other insect enemies. Dr. Arnold has made a curious ob- 

 servation (confirmed by Dr. Forsstrom with respect to others 

 of the genus) on the use of the long processes or tails that 

 distinguish the secondary wings of Thecla larbas. These 

 processes, he remarks, resemble antennae, and when the but- 

 terfly is sitting it keeps them in constant motion ; so that at 

 first sight it appears to have a head at each extremity ; which 

 deception is much increased by a spot resembling an eye at 

 the base of the processes. These insects, perhaps, thus 

 perplex or alarm their assailants. — Goedart pretended that 

 the anal horn with which the caterpillars of so many hawk- 

 moths (Sphingidce) are armed, answers the end of a sting 

 instilling a dangerous venom : but the observations of mo- 

 dern entomologists have proved that this is altogether fabulous, 

 since the animal has not the power of moving them. 1 Their 

 use is still unknown. 



Whether the long and often threatening horns on the 

 head, the thorax, and even elytra, with which many insects 

 are armed, are beneficial to them in the view under consider- 

 ation, is very uncertain. They are frequently sexual dis- 

 tinctions, and have a reference probably rather to sexual 

 purposes and the economy of the animal, than to any thing 

 else. They may, however, in some instances deter enemies 

 from attacking them, and therefore 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 tremen- 

 dous and effectual weapon with which insects are armed — 

 though this, except in the case of the scorpion, is also a 



i De Geer, i. 149. 



