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LETTER XXIII. 



MOTIONS OF INSECTS. Umago.-) 



III. The motions of insects in their perfect or imago state are various, 

 and for various purposes ; and the provision of organs by which they are 

 enabled to effect them is equally diversified and wonderful. It will be con- 

 venient to divide this multifarious subject ; I shall therefore consider their 

 motions under two principal heads : — motions of insects reposing — and 

 motions of insects in action ; — and this last head I shall further subdivide 

 into motions whose object is change of place, and sportive motions. 



The first of these, motions of insects reposing, will not detain us long. 

 The most remarkable is that of the long-legged gn ats or crane- flies ( TipulcB), 

 When at rest upon any wall or ceiling, sometimes standing upon four legs, 

 and sometimes upon five, you may observe them elevate and depress their 

 body alternately. This oscillating movement is produced by the weight 

 of their body and the elasticity of their legs, and is constant and uninter- 

 rupted during their repose. Unless it be connected with the respiration 

 of the animal, it is not easy to say what is the object of it. Moths when 

 feehng the stimulus of desire, or under alarm, set their whole body into a 

 tremor.^ A living specimen of the hawk-moth of the willow being once 

 brought to me, upon placing it upon my hand, after ejecting a milky fluid 

 from its anus, it put its wings and body in a most rapid vibration, which 

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

 Aurelians " The large skipper " (Hespeiia sijlvanus), 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. But- 

 terflies, when standing still in the sun, as you have doubtless often ob- 

 served, 



" Their golden pinions ope and close ; " 



thus, it should seem, unless this motion be connected with their respi- 

 ration, alternately warming and cooling their bodies. You have probably 

 noticed a very common little fly, of a shining black, with a black spot at 

 the end of its wings (^Seioptera vibrans~). It has received its trivial name 



1 Peck in Linn. Trans, xi. 92. 



* Meigen considers this as an Ortalis ; but its peculiar habit of constantly vi- 

 trating its wings indicates a distinct genus ; especially as the habit is not confined 

 to a single species. 



