MOTHS. 281 



within, and when the insect is fairly out, it shuts again of 

 its own accord, like a door with spring hinges, — a circum- 

 stance which at first puzzled Eoesel not a little when he 

 saw a fine large moth in his box, and the cocoon apparently 

 in the same state as when he had put it there. Another 

 naturalist conjectures that the converging threads are in- 

 tended to compress the body of the moth as it emerges, in 

 order to force the fluids into the nervures of the wings ; 

 for when he took the chrysalis previously out of the 

 cocoon, the wings of the moth never expanded properly.* 

 Had he been much conversant with breeding insects, he 

 would rather, we think, have imputed this to some injury 

 which the chrysalis had received. We have witnessed the 

 shriveling of the wings which he alludes to, in many 

 instances, and not unfrequently in butterflies which spin 

 no cocoon. The shriveling, indeed, frequently arises from 

 the want of a sufficient supply of food to the caterpillar in 

 its last stage, occasioning a deficiency in the fluids. 



The elasticity of the cocoon is not peculiar to the em- 

 peror-moth. A much smaller insect, the green cream- 

 border-moth ( Tortrix chlorana) before mentioned (page 149), 

 for its ingenuity in bundling up the expanding leaves of 

 the willow, also spins an elastic shroud for its chrysalis, of 

 the singular shape of a boat with the keel uppermost. 

 Like the caterpillar of Pyralis strigulalis (page 172), whose 

 building, though of difterent materials, is exactly of the 

 same form, — it first spins two approximating walls of 

 whitish silk, of the form required, and when these are 

 completed, it draws them forcibly together with elastic 

 threads, so placed as to retain them closely shut. The 

 passage of the moth out of this cocoon might have struck 

 Eoesel as still more marvellous than that of his emperor, 

 in which there was at least a small opening ; while in the 

 boat cocoon there is none. We have now before us two of 

 these, which we watched the caterpillars through the pro- 

 cess of building, in the summer of 1828, and from one only 

 a moth issued, — the other, as often happens, having died in 



* Meinecken, quoted by Kirby and Spence, ill. 280. 



