THE CHALCIS FLIES 



(Super-family Clialcidoidea.) 



This group of parasitic Hymenoptera is probably the largest 

 in number of species of any of the corresponding Hymenopterous 

 groups. It is a well defined and well limited group structurally 

 speaking and comprises undoubtedly many thousands of species. 

 Only a small proportion of the species have as yet been described. 

 As a rule the insects are so small that they attract no attention from 

 the average collector and the paucity of our specific knowledge 

 of the group possibly arises from this fact. The writer was the 

 first entomologist in America to undertake the systematic study of 

 the Chalcidoidea and he and his colleague, Mr. Ashmead, have 



had the field practically to 

 themselves for the past 20 

 years. In the course of this 

 time, however, we have 

 described many hundreds 

 of species and have learned 

 many interesting facts about 

 the strange life histories and 

 relationships with other in- 

 sects, many more of which 

 remain to be noted by care- 

 ful observers. Almost all 

 of the forms are truly parasitic, the exceptions being certain gall- 

 making species belonging to the genus Isosoma and its allies and 

 possibly the seed inhabiting species of the genus Megastigmus. 

 Nowhere in nature is there a more marked example of the co- 

 relation between structure and habits than occurs in this family. 

 This co-relation descends to the relation between the parasites and 

 their hosts so that it is possible for an experienced person on 

 seeing a new species of Chalcis fly to tell precisely what kind of 

 an insect it will be found to be parasitic upon. For example, the 



56 



Fig. 29. — Pachyneuron micans, How. 

 (Author's illustration.) 



