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LETTER XXIII. 



MOTIONS OF INSECTS. {Imago.) 



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

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

 enabled to eflect them is equally diversified and wonderful. It will be 

 convenient 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 sub- 

 divide 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 gnats or crane-flies {Tip- 

 ula). 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 uninterrupted 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 feeling 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 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 vibra- 

 tion, which continued more than a minute, when it flew away. A butter- 

 fly, called by Aurelians " The large skipper" (Hcspcria sylvanus), when 

 it aliglits, 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 arc merely those of parts. Butter- 

 flies, when standing still in the sun, as you have doubtless often observed, 



" Their golden pinions ope and close ; •' 



thu^. it should seem, unless this motion be connected with their respiration, 

 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 (Scioptera vibrans'^). It has received its trivial name 

 (yibrans) 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 arc very active with their antenna?, though their 

 bodies are at rest. I remember one evening attending for some time to 

 the proceedings of one of those caseworm-flies (Lepiocerus) , that are 



» Peck in Linn. Trans, xi. 92. 



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

 wings indicates a distinct genus ; especially as the habit is not confined to a single species. 



