CHAP. V. FLUIDS OF INSECTS. 157 



human ordure, that proceeds from its touch. Some of 

 the ants are equally offensive. Many insects emit their 

 smell from particular organs : thus, nearly the whole of 

 the caterpillars of the true butterflies (Papilio Fab.) 

 have two retractile horn-shaped processes, which, from 

 Bonnet's observations on the European species, emit a 

 strong smell, and are probably employed by the insect 

 to drive away the flies and ichneumons that annoy it. 

 De Geer mentions the larva of the Tenthredo, or saw-fly, 

 which throws out a most nauseous oclour, from some- 

 what similar organs, situated between the legs. The 

 larva of Chrysomela Populi emits a white milky fluid, 

 the smell of which, as De Geer says, is almost insup- 

 portable. But the most extraordinary insects possess- 

 ing this species of defence, are the beetles called 

 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 ; and this im- 

 mediately stops the progress of its assailant. When it 

 has recovered from the effects of this discharge,, and the 

 pursuit is renewed, a second, in like manner, arrests its 

 course. This little bombardier can fire its artillery 

 twenty times in succession, if necessary ; and so gain 

 time to effect its escape. Another species (Brachinus 

 displosor), by bending the joints of its abdomen, can 

 direct its smoke to any particular point. M. Leon 

 Dufour observes that this smoke has a strong and pun- 

 gent odour, very similar to that of nitric acid. It is 

 caustic, and produces on the skin the sensation of burn- 

 ing. 



(178.) The emission of fluids is another means of 

 defence possessed by insects. The Chrysomela tens- 

 bricosa Fab. (fig. 53.}, when handled, usually ejects from 

 its mouth drops of a red fluid, which stains paper of 

 an orange colour. Lesser, having once touched the anal 



