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LETTER XXIII. 
MOTIONS OF INSECTS. (Jmago.) 
Il. 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- 
yenient 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 gnats or crane-flies ( Tipule). 
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 
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 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, catled b 
Aurelians “ The large skipper” (Hesperia sylvanus), when it alights, whic 
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- 
ba 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. 
2 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. 
