164 HYMENOPTEEA (SAWFLIES). 



Ichneumon and Saw-flies (Hymenoptera-terebrantia). 



The Ichneumonidm (fig. 77, 5) and the Tenthredinidoe are the 

 two families to be considered here. The former are entomo- 

 phagous — that is, parasitic in the larvae of other insects — and 

 with a stalked abdomen and projecting ovipositor in the female. 

 The chief families are — 



(i) The Pteromalidce, whose larvae are parasitic in various 

 insect larvae and ova, and even in other parasites ; 



(ii) The Braconidm, which attack caterpillars and beetle- 

 larvae ; and 



(iii) The IchneumonidcB, which attack all larvae. 



The ova laid by these various insects hatch into little grubs, 

 which gradually devour their host, but not until they and their 

 host have nearly reached maturity, when they pupate either 

 within or external to their prey. The little yellow cocoons we 

 often see in abundance around the larvae of the Large Cabbage- 

 White (Pieris brassicce) in the autumn are the cocoons of one of 

 the Braconidae, Microgast&r g'lomeratus, which aids so much in 

 destroying these noxious larvae on our cabbages. 



Ichneumonidae vary much in size : some are microscopic, 

 while others are quite large. All, however, are equally bene- 

 ficial, and worthy of our protection. 



The Hessian-fly is largely parasitised by these insects ; so are 

 Aphides. We can nearly always find some dead plant-lice on 

 every tree — pearly looking bodies, often with a minute round 

 hole, showing where the Ichneumon has escaped. 



The Sawflibs and Wood-wasps. 



Sawflies and Wood-wasps are phytophagous, with sessile ab- 

 domen, the larvae resembling. caterpillars in the former group. 



(1) The Sawflies or Tenthredinidoe have a sessile abdomen, 

 with short saw-like borer of a complex structure, which is only 

 exserted during egg-laying. The mandibles are well formed, but 



