24 LETTERS ON ENTOMOLOGY. 
Mr. Smeathman tells us, that the Termites will 
in a few weeks destroy and carry away the trunks 
of large trees, without leaving a particle behind ; 
and in places where two or three years before 
there has been a populous town, if the inhabit- 
ants have abandoned it, there will be a very thick 
wood, and not a vestige of a post to be seen. 
You may easily imagine that if these kinds of 
insects, though so useful in some cases, were 
permitted to increase very much, we should 
not have even a gate or a post; but they are 
kept in due bounds by the number of enemies 
which make them their prey. Some are in- 
sectivorous only in the larva state, others only in 
the perfect state, others in both states, and others 
in all three. The parasitical insects feed upon 
the living creature, and only destroy it when 
they attain their full growth ; the imparasitical 
ones are those which prey upon dead insects, or 
kill them. The most beneficial of the latter race 
are those which devour the aphides or plant- 
lice. The larva of a beautiful fly is one which 
has a pair of long crooked mandibles perforated, 
and serving instead of a mouth; with these it 
sucks the aphides without mercy, and the in- 
dividuals of one species even clothe themselves 
in the skins of their victims. Another grub, 
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