MEANS OF DEFENCE OF INSECTS. 453 



has not a peculiar scent. — Some dipterous insects — though these in gene- 

 ral neither offend nor delight us by it — are distinguished by their smell. 

 Thus Mesembrina mysiacea, a fly that in its grub state lives in cow-dung, 

 savors in this respect, when a denizen of the air, of the substance in 

 which it first drew breath.^ And another (^Sepsis cynipsea) emits a fra- 

 grant odor of beaum.- — I have not much to tell you with respect to apte- 

 rous insects, except that lulus terrestris, a common millepede, leaves a 

 strong and disagreeable scent upon the fingers when handled.^ Most of 

 the insects I have here enumerated, probably, are defended from some 

 enemy or injury by the strong vapors that exhale from them; and, per- 

 haps, some in the list produce it from particular organs not yet noticed. 



I shall next beg your attention to those insects that emit their smell 

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

 vessels, which I shall call osmaUria ; while in others it issues from the 

 intestines at the ordinary passage. In the former instance the organ is 

 usually retractile within the body, being only exserted when it is used : it 

 is generally a bifid vessel, something in the shape of the letter Y. Linne, 

 in his generic character of the rove-beetles (^Staphylinida) , 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, particu- 

 larly 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 

 something extremely fetid with a spicy odor, 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 

 Machaon). 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. An- 

 chises and many other Equitcs'^, as also Parnassius Apollo. Another 

 insect, the larva of a species of saw-fly described by De Geer, is furnished 

 with osmateria, or scent-orgatjs, 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 odor, which remains long upon the finger ; but when the pres- 

 sure is removed they are withdrawn within the body.^ The grub of the 

 poplar-beetle (^Chrysomela Populi), also, is remarkable for similar organs. 

 On each of the nine intermediate 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 observes, is almost insupportable, being inex- 

 pressibly strong and penetrating. These drops proceed at the same instant 



1 De Geer, vi. 131. Meigen, Dipt. v. 12. " De Geer, vi. 135. 33. 



' Ibid. vii. 581. •* Merian Surinam, 17. Jones in Linn. Trans, ii. 64. 



» De Geer, ii. 989. t. xxxvii. f. 6. 



