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 feed 

 upon the caterpillar, penetrating to its very entrails. 

 These larvae, 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 Iarva3, 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 years 

 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 

 ",f his enemies by observing the activity of his friends. 



