2T4 



ELEMENTARY ZOOLOGY 



plete metamorphosis, and their habits and instincts are, 

 as a rule, very highly specialized. The parasitic Hymen- 

 optera such as the ichneumon flies, 

 chalcid flies, etc., are stingless but 

 have usually a piercing ovipositor 

 (the sting being only a modified 

 ovipositor). The general life-history 

 of these ichneumons is as follows: 

 the female ichneumon fly, finding 

 one of the caterpillars or fly or beetle 

 larvae which is its host, settles on it 

 and either lays an egg or several 

 eggs on it, or thrusting in its ovi- 

 positor, lays the eggs in the body; 

 the young ichneumon hatching as 

 a grub burrows into the body of its 

 caterpillar host, feeding on the body- 

 tissues, but not attacking the heart 

 FIG. 77._Water-tiger, the or nervous system, so that the host 



larva of the predaceous 



water-beetle, Dyticus sp. 

 (From specimen.) 



is not soon killed ; the ichneumon 

 pupates either inside the host, or 



crawls out and, spinning a little silken cocoon (fig. 160), 



pupates on the surface of the 



body or elsewhere. 



Some of the stingless Hymen- 



optera are not parasites, but are 



gall-producers. The female with 



its piercing ovipositor lays an 



egg in the soft tissue of a leaf or FIG. 78. The plum curcutio, 



stem, and after the larva hatches ConotraMus nenuphar a 



beetle very injurious to plums. 



the gall rapidly forms. The (Photograph by M. v. Slin- 

 larval insect lies in the plant- landt) 

 tissue, having for food the sap which comes to the rapidly 

 growing gall. It pupates in the gall, and when adult 

 eats its way out. 



