ICHNEUMONIDiE. 193 



palpi are three to four-jointed. The abdomen is inserted im- 

 mediately over the hind pair of trochanters, and usually consists 

 of seven visible segments. The fore-wings have one to three 

 subcostal (cubital) cells. 



The larva is a soft, fleshy, cylindrical, footless grub, the 

 rings of the body being moderately convex, and the head rather 

 smaller than in the foregoing families. The eggs are laid by 

 the parent either upon the outside or within the caterpillar, or 

 other larva, on which its young is to feed. When hatched it 

 devours the fatty portions of its victim which dies gradually of 

 exhaustion. The ovipositor of some species is very long, and 

 is fitted for boring through very dense substances ; thus Mr. 

 Bond, of England, observes that Rliyssa persuasoria actually 

 bores through solid wood to deposit its eggs in the larvae of 

 Sirex ; the ovipositor is worked into the wood like an awl. 

 "When about to enter the pupa state the larva spins a cocoon, 

 consisting in the larger species of an inner dense case, and a 

 looser, thinner, outer covering, and escapes as a fly through 

 the skin of the caterpillar. The cocoons of the smaller genera, 

 such as Cryptus and Microgaster, may be found packed closely 

 in considerable numbers, side by side, or sometimes placed up- 

 right within the body of caterpillars. 



The Ichneumon-flies are thus very serviceable to the agricul- 

 turist, as they must annually destroy immense numbers of cat- 

 erpillars. In Europe over 2,000 species of this family have 

 been described, and it is probable that we have an equal num- 

 ber of species in America ; Gcrstaecker estimates that there 

 are 4,000 to 5,000 known species. 



The Ichneumons also Y>vey on certain Coleoptera and Il3anon- 

 optera, and even on larvoe of Phryganidce^ vdnch live in the 

 water. In Europe, Pimpla Fairmairii is parasitic on a spider, 

 Clubione holosericea, according to Laboulbene. Boheman 

 states that P. ovivora lives on a spider, and species of Pimpla 

 and Heraiteles were also found in a nest of spiders, according to 

 Gravenhorst. Bouche says that Pimpla rufata devours, during 

 winter and spring, the eggs of Aranea diadema, and Ratzburg 

 gives a list of fourteen species of Ichneumons parasitic on 

 spiders, belonging to the genera Pimpla, Pezomachus, Ptero- 

 malus, Cryptus, Hemiteles, Microgaster, and Mesochorus. Mr. 

 13 



