242 PARASITES OF FLIES 



in the head. Two flies were very heavily infected. In one of 

 these twenty-three worms were present in the head and two in 

 the thorax, and in the other four worms were present in the 

 proboscis, eight in the thorax and ten in the head. 



The flies do not seem to be affected in any way by the 

 presence of the worms. 



(C) Parasites of the larvcB. 



Certain hymenopterous four-winged flies are accustomed to 

 frequent excreta, especially cow dung, in order to lay their eggs 

 in one of the many species of maggots that live there. Minute 

 forms, belonging to the sub-family Figitincu of the gall-fly family 

 Cynipidcs, are parasitic upon other insects, and also in dipterous 

 maggots. Some members of this group, F. antJioviyiarnm and 

 F. scjitellaris, have actually been bred from the larvai of house- 

 flies, and it is probable that others are parasitic on them. 



A number of species belonging to the super-family Clialci- 

 doidea, also live in the larvae of flies. " In the family Pteromalidcs 

 there is a genus Spalangia, which seems practically confined to 

 dipterous larvae. One species, Spalangia niger, was found by 

 Bouche to lay its eggs in the pupae of the house-fly, and to issue 

 in April and May. The larvae of the Spalangia are spindle- 

 formed and white, almost transparent, and are to be found in the 

 autumn in the puparia of the house-fly, where they destroy the 

 pupjE " (Howard, 191 1, p. 89). 



Howard also states that San ford observed a species named 

 S. imisccE in the pupae of house-flies, and that Stenoinabis 

 viuscariiDi has also been recorded from house-fly pupae. He also 

 quotes the interesting observations of Girault and Sanders, of the 

 University of Illinois, who obtained a species called Nasonia 

 brevicornis from the pupae of various flies. " It is a minute, dark, 

 metallic, brassy-green fly, with clear wings and a rather stolid 

 serious temperament. Girault and Sanders state that it heeds 

 external influences very slightly, and quietly and persistently 

 gives its whole attention to reproduction. They found that both 

 sexes crawled rapidly. The female is able to fly ; but the 

 favourite means of locomotion appears to be crawling. The 



