8 LETTERS ON ENTOMOLOGY. 
mentioned by Ulloa, common in Popayan, called 
coy a, or coyba, the venom of which is so malig- 
nant, that if it is only crushed on the skin, it 
penetrates the flesh and raises large tumours, 
which are soon followed by death; it is de- 
scribed as much smaller than a bug. 
As to the fly tribe, you will not deny their 
power of becoming a real plague. What would 
you think of any large animal coming to attack 
you with a tremendous apparatus of knives and 
lancets issuing from its mouth ? Yet the horse- 
fly, and many others which have instruments 
resembling all kinds of murderous weapons, at- 
tack you, and, forming a siphon or pump of 
them, suck your blood with the greatest voracity. 
Of all these little torments, the gnat species is 
the worst. They may be truly said to have their 
sting in the mouth, since the pain and swelling 
of the bite show that they inject poison. This 
weapon is composed of five pieces besides the 
sheath, some of which appear simply lancets, 
while others are barbed like a bee's sting, and 
are adapted both for making the wound, and 
forming a siphon to draw out the blood. 
Although with us, they are rather teasing 
than absolutely injurious, yet when they come 
in great numbers they are a true plague. In the 
