200 



MEANS OF DEFENCE OF INSECTS* 



moved they are withdrawn within the body. 1 The grub of 

 the poplar-beetle (Chrysomela Populi), also, is remarkable for 

 similar organs. On each of the nine intermediate dorsal seg- 

 ments of its body is a pair of black, elevated, conical tubercles 

 of a hard substance ; from all of these when touched the ani- 

 mal emits a small drop of a white milky fluid, the smell of 

 which, De Geer observes, is almost insupportable, being in- 

 expressibly 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 moment and dispensing its perfume, is with- 

 drawn again within its receptacle, till the pressure is repeated, 

 when it re-appears. 2 



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 (Brachinus), The most common 

 species (B. 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 smoke attended 

 by a very disagreeable scent, is seen to proceed from its anus, 

 which immediately stops the progress of its assailant : when 

 it has recovered from the effect of it, and the pursuit is re- 

 newed, a second discharge again arrests its course. The bom- 

 bardier can fire its artillery twenty times in succession if ne- 

 cessary, and so gain time to effect its escape ; and what is still 

 more remarkable, Mr. Holme found that by pressing the ab- 

 domen near the anus, the discharges may be produced after 

 death. In this way two specimens which had been dead 

 eighteen hours, gave one fifteen and the other nineteen dis- 

 charges before being exhausted, and he even obtained explo- 

 sions from some specimens which had been dead four days ; 

 but most of these along with the noise discharged a black 



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



2 Ibid. v. 291. Compare Ray's Letters, 43. 



