HYMENOPTERA 915 



GG. Mesopleura divided by a transverse suture into an upper and 

 lower plate. Coxag very large and long ; the legs long and usually 



distinctly spinose. p. 933 PoMPiLiDiE 



DD. First abdominal segment forming a "scale" or "node" between the 

 propodeum and the gaster. Thorax with its sutures distinct, but the 

 mesothorax usually much reduced in size. p. 937 Formicid^ 



SuPERFAMiLY ICHNEUMONOIDEA 



The Ichneumon-flies and their Allies 



When the discouraged farmer sees his crops harvested before due 

 time by hordes of hungry insects, he is apt to long for a miracle to 

 remove the plague from his fields. Oftener than he dreams the miracle 

 takes place, and millions of insect pests never live to lay their eggs 

 for another brood. Such miracles are most frequently wrought by 

 members of a large group of insects, which is commonly known as 

 the parasitic Hymenoptera, and by the tachina-fiies discussed in the 

 chapter treating of the Diptera. 



Although some of these insects are external parasites, most of 

 them live within the bodies of their hosts, within which they pass 

 their entire larv^al existence. Their presence in this strange situation 

 is due to the fact that the parent lays her eggs within or upon the 

 body of the victim. When the egg is laid upon the body of the 

 victim the larva as soon as it hatches bores its way into the body. 

 So in either case the young parasite is in the midst of suitable food. 

 It is probable that the parasite feeds at first only on the blood of 

 its host; hence the parasitized insect is not destroyed at once, but 

 lives on with the parasite within it, which gradually attains its growth. 

 Finally, the parasitized insect perishes; and from the larva that has 

 been noiu-ished in its body there is developed a winged creature, 

 which in turn lays its eggs in other victims. Frequently a parasitic 

 insect lays several eggs within a single victim, so that a number of 

 parasites may be developed within the body of a single insect. Each 

 species of these parasites infests only certain insects, each insect hav- 

 ing, to a great extent, its peculiar parasites. 



It has been proposed recently to term these insects that eventually 

 kill their victims parasitoid instead of parasitic, on the ground that 

 they are not true parasites but "extremely economic predators." 

 (See Wheeler ('23), page 46). In the preparation of this work, it has 

 seemed best to continue the use of the term parasite in the broad 

 sense in which it is generally used by entomologists. 



The parasitic Hymenoptera does not constitute a natural division 

 of the order but includes representatives of several superfamilies, of 

 which the Ichneumonoidea is one. 



The Ichneimionoidea is the largest of the superfamilies of the 

 Hymenoptera, except the Chalcidoidea, including hundreds of genera 

 and many thousand species. All of the species are parasitic; eggs, 

 larvae, pupae, and even adult insects are infested by them; and mem- 

 bers of nearly all of the orders of insects are subject to their attacks. 

 They are therefore, of extremely great economic importance. 



