LETTERS ON ENTOMOLOGY. 143 
seen a great number on a vine, in the green- 
house, of an oblong shape. The male is a beau- 
tiful little fly, the body, head, and legs of which 
are of a deep red ; the wings are very large in 
proportion, semi-transparent and whitish, with a 
border of bright red, which is their greatest or- 
nament. On the tail, which is long and pointed, 
are two white filaments twice as long as the 
wings. It is singular that there should be so 
striking a difference between individuals of the 
same species, but it is not the only instance ; the 
glow-worm is a similar one. 
I should have told you that they change their 
skins or rather shells, but in a different manner 
from other insects. They make various move- 
ments and contortions, which split the outer 
surface into thin transparent laminae or flakes, 
which fall off; but as they are extremely slow 
in their motions, this takes a long time to per- 
form. 
The Cochineal insect, the Kermes, or Coccus 
Bapkica, are of this species ; but Reaumur calls 
them false Gall insects, from some differences 
peculiar to them. The Cochineal, which is one 
of the greatest objects of commerce in Mexico, 
and is cultivated in that country alone, feeds on 
a plant known by the names of opuntia, Indian 
