INSECTS BENEFICIAL AND BEAUTIFUL 249 



the white-marked tussock moth. A favorite time for the 

 Pimpla to sting her victim is while the caterpillar is spin- 

 ning its cocoon ; and if a number in this stage are placed 

 in an open window in the schoolroom, it is quite possible 

 that a Pimpla may come and show how she does her work. 

 The eggs of the Pimpla hatch into whitish larvae, which 

 feed actively and attain their growth in about four days. 



FIG. 103. TOMATO SPHINX LARVA 

 With parasites emerging ; 268 are out or in sight. (Natural size) 



They then spin slender yellowish-brown cocoons, transform 

 into pupae, and emerge in about ten days as adult ichneu- 

 mons ; so that the whole life story from egg around to egg 

 may not require more than fifteen days to be completed. 



Until recently all the four-winged parasitic insects were 

 called ichneumon flies. Now the group has been much 

 subdivided ; but since the distinctions upon which these 

 divisions have been made are mostly minute and technical, 

 we may leave them to specialists. It will be sufficient, 

 for elementary work, if we gain some clear ideas of the 

 r61e that parasitic insects play in nature. 



