244 



LETTER XXIII. 



MOTIONS OF INSECTS. (Imago.) 



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 convenient to divide 

 this multifarious subject ; I shall therefore consider their mo- 

 tions 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 de- 

 tain us long. The most remarkable is that of the long-legged 

 gnats or crane-flies ( Tipulce). 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. 1 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 vibration, which continued 

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

 by Aurelians cc 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. 



1 Peck in Linn. Trans, xi, 92. 



