376 Annals Entomological Society of America [Vol. XII, 



of the 111 nestlings died. That there were no more fatalities 

 is perhaps to be explained by the fact that more than half of 

 the thirty-three infested nests were those of comparatively 

 large birds, the Western Robin and the Oregon Towhee. 



The nest infested by the larvas of Phormia metallica Town- 

 send was that of a Western Robin and contained three nestlings. 

 When the latter took wing, twenty-six larvae were taken from 

 the nest. The larvas pupated in a few days and both larvae 

 and pup£e looked so much like those of Phormia azurea Fallen 

 that the writer was unaware that he was dealing with a new 

 fly until the adults emerged. From the facts at hand it seems 

 probable that Phormia metallica Townsend, both as larva and 

 adult, is similar in habit to that of its near relative, Phormia 

 chrysorrhea Meigen. 



The six nests infested by the larv^ of Hylemyia nidicola 

 Aldrich offered an entirely different aspect. When discovered 

 four of them contained the remains (only bones and feathers) of 

 nine, nearly full-fledged nestlings. From these four nests, 283 

 pupag were taken nearly all of which later hatched. The 

 remaining two nests infested by the larvee of Hylemyia nidicola 

 Aldrich were those of a Cliff Swallow and a Yellow Warbler and 

 contained one and five dead nestlings respectively. In these 

 two nests the larvae were still at their repast. Fifty-nine 

 larvae were picked from the outer surface of the six dead birds, 

 though many more could undoubtedly have been obtained from 

 within the nestlings. None of the six nests infested by the 

 larvae of Hylemyia nidicola Aldrich contained any living nest- 

 lings when discovered, but judging by the small number of 

 dead birds in most of the nests, it seems possible that some 

 of the nestlings may have survived. 



The larva of Hylemyia nidicola Aldrich is much smaller 

 than that of Phormia azurea Fallen and measures about 8 mm. 

 in length and 2 mm. in width when mature. It apparently 

 is not blood-sucking in habit like the larvae of Phormia azurea 

 Fallen, Phormia chrysorrhea Meigen, and other Muscidae. The 

 pupa^ measures about 5 mm. in length and 2.5 mm. in width 

 and is of a glossy, golden-brown color. 



^ It is identical in size and appearance with the seventy-one secured near 

 Berkeley, California, the preceding summer (Cf. a. The Condor, Vol. XXI, pp. 

 36-37. b. Univ. Calif. Publ. ZooL, Vol. XIX, pp. 196-197). 



