142 



NATURAL HISTORY OF INSECTS. 



first gnaw their way out of the larva or pupa in which they 

 live, and then each one spins a cocoon around its body; some- 

 times they spin a mass of flossy silk, and then crawl into this 

 and there spin their cocoons. Occasionally only one parasitic 

 larva lives in a larva or pupa, but sometimes several dozen 



Fig. 333. 



inhabit one and the same pupa or larva. When the egg was 

 deposited in the body of a larva, the larva sometimes passes to 

 the pupa stage before the parasitic Ichneumon-fly issues. 



Fig. 334. 



The Chalcis-flies form another group of insects which live 

 parasitical in the egg, the Iarva3, or the pupae of other insects; 

 they are very small, and their wings are provided with but few 

 veins (Figs. 333 and 334). They live principally in the eggs 

 of other insects, and many kinds infest various kinds of Scale- 

 insects and Plant-lice. 



Another class of parasitic insects are the Tachina-flies (Fig. 

 230). These flies attach their white eggs to the bodies of cater- 

 pillars, etc., and the larvae which hatch from these eggs gnaw 



