The Ichneumon Fly. 581 
the Ichneumon or Mangouste destroys the crocodile in 
the East. The tip of the abdomen of the females is 
armed with an ovipositor, visible in some species, though 
not in others ; and this instrument, though so fine, is 
able to penetrate through mortar and plaster. The 
female fly uses it to deposit her eggs in the body of 
other insects when in the egg, caterpillar, or pupa state ; 
so that the young as soon as they are hatched may fesd 
upon the caterpillar, penetrating to its very entrails. 
These larva?, however, contrive to suck out the nutri- 
tious juices of their prey without attacking its vitals ; for 
the caterpillar continues to live for a long time, so as to 
afford them food till they have attained their full size. It 
is not uncommon to see caterpillars fixed upon trees, as if 
they were sitting upon their eggs ; when it is afterwards 
discovered that the larvae, which were within their bodies, 
have spun their threads, with which, as with cords, the 
caterpillars are fastened down, and so perish miserably. 
" A friend of mine," says Dr. Derham, " put about 
forty large caterpillars, collected from cabbages, on some 
bran and a few leaves in a box, and covered it with 
gauze to prevent their escape. After a few days we saw, 
from the backs of more than three-fourths of them, about 
eight or ten little caterpillars of one of the Ichneumon 
flies come out and spin each a small cocoon of silk ; and 
in a few days the large caterpillars died." 
The Ichneumons performed great service in the j'ears 
1731 and 1732, by multiplying in the same proportion as 
the caterpillars, and their larvae destroyed more of these 
destructive creatures than could any efforts of human 
industry. 
They are found of all sizes, suitable to the various 
insects they are parasitic upon, and in their ceaseless 
rummaging about in every hole and corner, millions of 
destructive larvae are discovered and destroyed by them, 
which would otherwise have reached maturity, and left 
a progeny to renew their ravages in the ensuing summer. 
Even those larvae which feed in concealment are readily 
discovered by the Ichneumons destined to live upon 
them, and the farmer is often made aware of the presence 
of his enemies by observing the activity of his friends. 
