270 



BENEFICIAL INSECTS. 



already living in the body of a caterpillar ; we then have one ichneumon 



parasitic upon another, a 

 singular phenomenon, which 

 checks the too great increase 

 of the beneficial insects 

 (fi g. 3 2 3) . Ichneumon s al so 

 lay their eggs in such small 

 insects as aphides, and even 

 in the eggs of insects. 

 One species lays its eggs in 

 the eggs of the moth-borer 

 of sugarcane and the eggs 

 of many insects are thus 

 destroyed. 



Besides the ichneumons, 

 there are the parasitic flies, 

 a large group of Diptera 

 which behave very similarly 

 to the ichneumons. These 

 flies (fig. 325) resemble 

 house-flies and are common 

 in the fields. They lay 

 their eggs on caterpillars, 



and other insects, the maggot that hatches destroying the caterpillar. 



As in other flies, the full grown 



maggot forms a brown seed-like 



pupa (fig. 324) usually coming 



out of the caterpillar before it 



does so. A species of parasitic 



fly lays its eggs on the Bombay 



Locust and another on the Bed 



Cotton Bug. 



As a rule every species of 



parasite is found only on one or 



a few insects. The parasite 



T?Tf3. Q9f\ 



of the Cotton Stem-borer is not ' 



. , __ ., The parasite of the maggot of the Bice btem 



the same as that or the Moth- jiy. (Magnified.) 



borer of sugarcane. Parasites 



that we rear from distinct insects are usually distinct themselves, though 

 the same parasite may be found in two species of insects which are 

 very much alike. Every abundant caterpillar and very many beetle 



FIG. 325. 



Fly whose maggot is a parasite on leaf-eating 



caterpillars. (Magnified.) Pupa 



beloiv, natural size. 



