160 SAWFLIES, ICHNEUMON-FLIES, WASPS, ETC. 



as Gall-flies, more or less resembling the one figured;: 

 but they are not mentioned for special attention now, 

 but merely to notice their existence. 



Fig. 124. — Spangle-galls on Oak-leaf ; ditto, magnified. 



The families of the Parasite Wasp-flies are im- 

 portant to us, as a means of keeping the increase of 

 other insects in check. 



One division of these is that of the Ichneumon 

 Flies {IchneumonidcE) . These are much like the 

 Ichneumon parasite of the Corn Sawfly. They are 

 lightly-made insects, with a longish body and abdo- 

 men ; long legs ; a small head with long horns, often 

 having a ring of white on them ; and an ovipositor, 

 sometimes short, sometimes long, and often perma- 

 nently extended like a large and long sting. With 

 this they insert their eggs, for the most part into the 

 grubs of other insects, but sometimes into their eggs, 

 and occasionally into the chrysalids ; and those kinds 

 furnished with long ovipositors pierce with them 

 through bark or solid wood, and thus insert their 

 eggs into Beetle grubs, or whatever their selected 

 victim may be, which, although out of sight, their 

 instinct tells them is within, ready to act as food to 

 their maggots ; and thus they give us help which 

 nothing else affords. 



In the case of Corn-ears which are infested by 

 Aphides, many of the Aphides, instead of being of the 



