HABITATIONS OF INSECTS. 261 



merely a mechanician, but a profound natural philosopher, well acquainted 

 with the properties of air, it has another resource when any extraordinary 

 violence threatens to overturn its slender turret. It forms a vacuum in 

 the protuberance at the base, and thus as effectually fastens it to the leaf 

 as if an air-pump had been employed ! This vacuum is caused by the 

 insect's retreating on the least alarm up its narrow case, which its body 

 completely fills, and thus leaving the space below free of air. In detach- 

 ing one of these cases you may easily convince yourself of the fact. If 

 you seize it suddenly while the insect is at the bottom, you will find that 

 it is readily pulled off, the silken cords giving way to a very slight force ; 

 but if, proceeding gently, you give the insect time to retreat, the case will 

 be held so closely to the leaf as to require a much stronger effort to loosen 

 it. As if aware that, should the air get admission from below, and thus 

 render a vacuum impracticable, the strongest bulwark of its fortress would 

 be destroyed, our little philosopher carefully avoids gnawing a hole in the 

 leaf, contenting itself with the pasturage afforded by the parenchyma above 

 the lower epidermis ; and when the produce of this area is consumed, it 

 gnaws asunder the eords of its tent, and pitches it at a short distance as 

 before. Having attained its full growth, it assumes the pupa state, and 

 after a while issues out of its confinement a small brown moth, with long 

 hind legs, the Phalcena Tinea serratella of Linne. 1 



Some larva?, which form their covering of pure silk, are not content 

 with a single coating, but actually envelop themselves in another, open on 

 one side, and very much resembling a cloak ; whence Reaumur called them 

 " Teignes a fourreau a manteau" What is very striking in the construc- 

 tion of this cloak is, that the silk, instead of being woven into one uniform 

 close texture, is formed into numerous transparent scales overwrapping each 

 other, and altogether very much resembling the scales of a fish. 2 These 

 mantle-covered cases, one of which I once had the pleasure of discovering, 

 are inhabited by the larva of a little moth apparently first described by Dr. 

 Zincken genannt Sommer, who calls it Tinea paUiatella? 



Various substances besides silk are fabricated into habitations by other 

 larva?, though usually joined together either with silk or an analogous 

 gummy material. Thus Diurnea? lichenum forms of pieces of lichen a 

 dwelling resembling one of the turreted Helices, many of which I observed 

 in June, 1812, on an oak in Barham. The larva of another moth, which 

 also feeds upon lichens, instead of employing these vegetables in forming 

 its habitation, composes it of grains of stone eroded from the walls of 

 buildings upon which its food is found, and connected by a silken cement. 

 These insects were the subject of a paper in the Memoirs of the French 

 Academy 4 , by M. de la Voye, who, from the circumstance of their 

 being found in great abundance on mouldering walls, attributed to them 

 tfie power of eating stone, and regarded them as the authors of injuries 

 proceeding solely from the hand of time ; for the insects themselves are 

 so minute, and the coating of grains of stone composing their cases is so 

 trifling, that Reaumur observes they could scarcely make any perceptible 

 impression on a wall from which they had procured materials for ages. 5 



1 Goeze, Natur. Menschenleben und Vorsehung. Anderson's Recreations, ii. 409. 

 See above, p. 8. 



2 Reaum. iii. 206. 5 Germar's Mag. fur Entomologie, i. 40. 

 4 x. 458. 5 Reanm. iii. 183. 



S 3 



