274 



The Orders of Insects 



close together. The trochanters have two segments. The females are 

 provided with ovipositors which in some cases are several times as long 

 as the body ; by means of these they lay their eggs in the bodies of 

 caterpillars. The forms with exceptionally long ovipositors, such as 

 Rhyssa (fig. 151), prey upon wood-boring grubs; this species lays her 

 eggs in the burrows of Sirex on whose grubs her larvse feed as 

 external parasites; in most cases, however, the ichneumon maggots 

 feed internally on the juices of their victims. Over 6000 species of 

 IchneumonidjE are already known, and the family is distributed in all 

 parts of the world (158, 159)- 



Braconidae. — The BraconiJa are a large family, closely allied to the 

 Ichneumonidse, but distinguished by having only a single cell on the 

 fore-wing between the cubitals and the second posterior cell. The 



Fig. 151. — Rhyssa persuasoria (Linn.), Europe, female ovipositing. From 

 Riley, Insect Life, vol. i (U.S. Dept. Agr.). 



larvse live like those of the Ichneumons, and the range of the family 

 is equally wide (158 b). 



Chalcididae. — The Chalddlda are a very large family of small 

 Hymenoptera distinguished from all the preceding families of 

 Petiolata by their elbowed feelers, which have from seven to thirteen 

 segments. The pronotum is partially free and does not reach back to 

 the insertion of the fore-wings. The neuration is very simple ; a 

 single thick nervure runs from the base of the wing to the costa, 

 giving off at its termination a very short branch. The trochanters 

 are divided. The Chalcididse are frequently of brilliant metallic 

 colours ; over 4000 species have already been described and they 

 occur in all parts of the world. The eggs are laid in galls, or in nests 

 of the higher Hymenoptera so that the larva may feed on the 



