PREDACEOUS AND PARASITIC INSECTS 



47 



the dragon %, poised in air and 

 waiting to pounce on some unwary 

 gnat or fly, is predaceous. 



A parasitic insect, on the other 

 hand, usually is higWy specialized 

 for existence on some particular species 

 of host, and has reached such depend- 

 ence on its host that if the latter 

 dies before the parasite has completed 



Fig. 48. — Larva, showing 

 exit holes of parasites. 

 Original. 



Fig. 49. 



Eggs of a parasite on a cut- 

 worm. Original. 



its life round, the parasite perishes. Many parasitic insects live 

 within the bodies of their hosts. A familiar example is found in the 

 species that lays its eggs in the body of the tomato worm, the 

 parasitic grubs finally gnawing their waj^ to the surface, where they 

 spin tiny, white cocoons on the bod}^ of their host. 



For most of us, the 

 tremendous work of para- 

 sitic and predaceous spe- 

 cies in destroying insect 

 pests passes unnoticed. 

 It is brought to mind 

 when we see or hear of 

 a bad outbreak of some 

 injurious insect, and later 

 observe that the threaten- 

 ing species has suddenly grown scarce — eometimes seemingly disap- 

 peared from the face of the earth in the very localities where it 

 had been abundant. If we were to follow up such cases carefully, 

 we should find, as a rule, that as soon as the threatening species 



Fiu. 50. 



Cocoons of parasites on 

 Original. 



lar\a. 



