MEANS OF DEFENCE OF INSECTS. 197 



plants and vegetable substances, insects, of any part of the 

 creation, afford the greatest diversity of odours. In the 

 Coleoptera order a very common beetle, the whirlwig ( Gyrinus 

 natator\ will infect your finger for a long time with a dis- 

 agreeable rancid smell ; while two other species, G. minutus 

 and villosus, are scentless. Those unclean feeders, the carrion 

 beetles (Silpha L.), as might be expected from the nature of 

 their food, are at the same time very fetid. Pliny tells us 

 of a Blatta, which, from his description, is evidently the 

 darkling-beetle {Blaps mortisaga), and which he recommends 

 as an infallible nostrum, when applied with oil extracted 

 from the cedar, in otherwise incurable ulcers, that was an 

 object of general disgust on account of its ill scent, a cha- 

 racter which it still maintains 1 ; which scent, from Mr. 

 Thwaites's investigation of the internal anatomy of this 

 insect, proceeds from two small oblong vesicles near the anus, 

 the fluid contents of which, when they are extracted and 

 dissected under water, rise in a bubble to the surface, and 

 there becoming vaporised diffuse the fetid smell peculiar to 

 this species. Numbers of the ground-beetles (Eutrechina) 

 that are found under stones, and in places that have not a 

 free circulation of air, exhale a most disagreeable and pene- 

 trating odour, which De Geer observes resembles that of 

 rancid butter, and is not soon got rid of. It is produced, he 

 says, from an unctuous matter that transpires through the 

 body 2 ; but I am rather inclined to think it proceeds from 

 the extremity. I have noticed that some small beetles of the 

 Omalium genus, for instance O. rivulare, and another species 

 that I once found in abundance on the primrose ( O. Primulm 

 K. Ms.), especially the latter, are abominably fetid when 

 taken, and that it requires more than one washing to free the 

 fingers from it. Every one knows that the cock-roach 

 {Blatta orientalis), belonging to the Orthoptera order, is not 

 remarkable for a pleasant scent ; but none are more notorious 

 for their bad character in this respect than the bug tribe 

 (GeocoriscB), which almost universally exhale an odour that 

 mixes with the scent of cucumbers another extremely un- 



1 Hist. Nat. t xxix. c. 6. 



o 3 



- iv. 86. 



