66 THE LIFE-STORY OF INSECTS [CH. 



to the presence of the larva by forming a character- 

 istic growth, the gall, pathological but often regular 

 and shapely, in whose hollow chamber the grub 

 lives and eats. Ichneumon-flies and their allies pierce 

 the skin of caterpillars and other insect-larvae, laying 

 their eggs within the victims' bodies, which their 

 grubs proceed to devour internally. Some very small 

 members of these families are content to lay their 

 eggs within the eggs of larger insects, thus obtaining 

 rich food-supply and effective protection for their 

 tiny larvae. In Platygaster and other genera of the 

 family Proctrotrypidae, M. Ganin (1869) showed the 

 occurrence of hypermetamorphosis somewhat like 

 that already described as occurring among the Oil- 

 beetles (Meloidae). The larva of Platygaster is at 

 first rather like a small Copepod crustacean, with 

 prominent spiny tail-processes; after a moult this 

 form changes into the legless grub characteristic of 

 the Hymenoptera, among which larvae even approach - 

 ing the campodeiform type are very exceptional. 

 The species of Platygaster pass their larval stages 

 within the larvae of gall-midges. 



Wasps, bees and ants, have the ovipositor of the 

 female modified into a sting, which is often used tor 

 the purpose of providing food for the helpless grubs. 

 Thus the digging wasps (Sphegidae and Pompilidae) 

 hunt for caterpillars, spiders, and other creatures 

 which they can paralyse with their stings, and bury 



