BENEFICIAL INSECTS. 405 



keeping down green-fly, &c., and may often be found amongst these 

 pests. 



The most important parasite insects belong to the order Hymen- 

 optera, and the following concise account of the families which may 

 be considered as beneficial is taken from Professor Carpenter's work 

 on ' Insects, their Structure and Life ' : — 



"Ichneumonidae.— The Ichneumonidai or Ichneumon -flies are an 

 exceedingly large family. The feelers are straight, long, and many- 

 jointed, tapering towards the tip ; three ocelli are always present on 

 the crown. The wings have for the Hymenoptera a complex neura- 

 tion ; a distinguishing character is the presence of two cells between 

 the cubitals and the second posterior cell (at the anal angle of the 

 fore-wing). Earely wings are quite absent. The stalk of the elongate 

 hind-body is attached to the lower or hinder of the first abdominal 

 segment, which is very large, while the metathorax is relatively short, 

 so that the middle and hind pairs of legs are inserted 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 : l)y means of these they lay their eggs in the bodies of cater- 

 pillars. The forms with exceptionally long ovipositors, such as 

 lihyssa, prey upon wood-boring grubs : this species lays her eggs in 

 the burrows of Sirex, on whose grubs her larvae feed as external 

 parasites. In most cases, however, the Ichneumon maggots feed in- 

 ternally on the juices of their victims. Over 6000 species of Ichneu- 

 monidse are already known,, and the family is distributed in all parts 

 of the world. 



" Braconidae. — Tlie Braconiclce are a large family, closely allied to 

 the Iclineumonida', but distinguished by having only a single cell on 

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

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

 is equally wide. 



" Chalcididse. — The Clialcidida' are a very large family of small 

 Hymenoptera, distinguished from all the preceding families of Petio- 

 hda 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 Chalcididge are frequently of brilliant metallic 



