418 MEANS OF DEFENCE OF INSECTS. 



particular organs. Of these some are furnished with a kind of scent-vessels 

 which I shall call osmateria ; while in others it issues from the intestines 

 at the ordinary passage. In the former instance the organ is usually re- 

 tractile within the body, being only exserted when it is used : it is gene- 

 rally a bifid vessel, something in the shape of the letter Y. Linne, in his 

 generic character of the rove-beetles (Siaphylinidts'), mentions two oblong 

 vesicles as proper to this genus. These organs, which are by no means 

 common to the whole genus, even as restricted by late writers, are its 

 osmateria, and give forth the scent for which some species, particularly 

 Ocypus brunnipes, are remarkable. If you press the abdomen hard, you 

 will find that these vesicles are only branches from a common stem ; and 

 you may easily ascertain that the smell of this insect, which mixes some- 

 thing extremely fetid with a spicy odour, proceeds from their extremity. 

 A similar organ, half an inch in length, and of the same shape, issues from 

 the neck of the caterpillar of the swallow-tail-butterfly (Papilio Ma- 

 chaon). When I pressed this caterpillar, says Bonnet, near its anterior 

 part, it darted forth its horn as if it meant to prick me with it, directing it 

 towards my fingers ; but it withdrew it as soon as I left off pressing it. 

 This horn smells strongly of fennel, and probably is employed by the insect, 

 by means of its powerful scent, to drive away the flies and ichneumons that 

 annoy it. A similar horn is protruded by the slimy larva of P. Anchises 

 and many other Eqvites 1 , as also Parnassius Apollo. Another insect, the larva 

 of a species of saw-fly described by De Geer, is furnished with osmateria, or 

 scent-organs, of a different kind. They are situated between the first five 

 pair of intermediate legs, which they exceed in size, and are perforated at 

 the end like the rose of a watering-pot. If you touch the insect they shoot 

 out like the horns of a snail, and emit a most nauseous odour, which re- 

 mains long upon the finger ; but when the pressure is removed they are 

 withdrawn within the body. 2 The grub of the poplar-beetle (Chrysomcla 

 Populi] also is remarkable for similar organs. On each of the nine inter- 

 mediate dorsal segments of its body is a pair of black, elevated, conical 

 tubercles of a hard substance ; from all of these when touched the animal 

 emits a small drop of a white milky fluid, the smell of which, De Geer ob- 

 serves, is almost insupportable, being inexpressibly strong and penetrating. 

 These drops proceed at the same instant from all the eighteen scent-organs ; 

 which forms a curious spectacle. The insect, however, does not waste 

 this precious fluid : each drop instead of falling, after appearing for a mo- 

 ment and dispensing its perfume, is withdrawn again within its receptacle, 

 till the pressure is repeated, when it re-appears. 3 



I shall now introduce you to the true counterparts of the skunk, which 

 explode a most fetid vapour from the ordinary passage, and combat their 

 enemies with repeated discharges of smoke and noise. The most famous 

 for their exploits in this way are those beetles which on this account are 

 distinguished by the name of bombardiers (BracMnus). The most common 

 species (2?. crepitans), which is found occasionally in many parts of Britain, 

 when pursued by its great enemy, Calosoma inquisitor, seems at first to have 

 no mode of escape : when suddenly a loud explosion is heard, and a blue 



1 Merian Surinam, 17. Jones in Linn.Trans. ii. 64. 



2 De Geer, ii. 989. t. xxxvii. f. 6. 



5 Ibid. v. 291. Compare Kay's Letters, 43. 



