MOTIONS OF INSECTS. 301 



a tremor a . A living specimen of the hawk-moth of the 

 willow being once brought me, upon placing it upon my 

 hand, after ejecting a milky fluid from its anus, it put 

 its wings and body into a most rapid vibration, which 

 continued more than a minute, when it flew away. A 

 butterfly, called by Aurelians " The large skipper," 

 (Hesperia Sylvanus,) when it alights, which it does very 

 often, for they are never long on the wing, always turns 

 half-way round ; so that, if it settles with its head from 

 you, it turns it towards you. 



Others of the motions in question are merely those of 

 parts. Butterflies, when standing still in the sun, as you 

 have doubtless often observed, 



" Their golden pinions ope and close ; " 



thus, it should seem, unless this motion be connected 

 with their respiration, alternately warming and cooling 

 their bodies. You have probably noticed a very com- 

 mon little fly, of a shining black, with a black spot at 

 the end of its wings (Seioptera vibrans b ). It has receiv- 

 ed its trivial name (vibrans) from the constant vibration 

 which, when reposing, it imparts to its wings. This 

 motion also, I have reason to think, assists its respiration. 

 Some insects when awake are very active with their 

 antennae, though their bodies are at rest. I remember 

 one evening attending for some time to the proceedings 

 of one of those case worm-flies (Leptocerus), that are re- 

 markable, like certain moths, for their long antenna?. It 

 was perched upon a blade of grass, and kept moving 



9 Peck in Linn. Trans, xi. 92. 



b Meigen considers this as an Ortalis ; but its peculiar habit of con- 

 stantly vibrating its wings indicates a distinct genus : especially as 

 the habit is not confined to a single species. 



