152 MISC. PUBLICATION 631, U. S. DEPT. OF AGRICULTURE 



nation of the feces, since it has been demonstrated that larvae may, on 

 occasion, seek out fresh excrement; however, others seem to be authen- 

 tic. Some records may be misidentification of other species of Tubifera 

 or related genera; nevertheless, some have been derived from reared 

 specimens. Two cases of occurrence within the vagina of a cow are 

 on record. 



Important references relating to the pathogenesis of this and related 



Figuke 91. — Tubifera tenaoc, adult female. 



species are Hall and Muir (-57), Hall (SO), and Bacigalupo and co- 

 workers (9). 



TUBIFERA DIMIDIATA (Wiedemann) 



Synonym. — EristaUs dimidiatus Wiedemann. 



Recognition Chaeactees. — Adult : This is a beelike fly with a uniformly black 

 thorax and predominantly black abdomen, which does, however, have narrow yel- 

 low apices to the segments and a pair of yellow side spots on segment 2 and some- 

 times also on segment 3. The arista has a few hairs on its basal third that are 

 longer than its diameter ; the face is shining On and around the prominence, and 

 usually with a brownish or blackish median stripe. The postalar callus is pro- 

 vided with a number of blackish hairs. The abdomen is mainly shining ; the third 

 segment has a round basal spot and an interrupted subapical band of opaque 

 black ; similar opaque areas on the second segment are more extensive, but on the 

 fourth segment only the basal round spot is present. Length, about 12 mm. 

 Larva : No satisfactory distinguishing characters can be given at present. 



Geogeaphical Disteibution. — Nearctic Region : Nova Scotia, Ontario, Quebec, 

 Alberta, Maine, New Hampshire, Vermont, Massachusetts, Rhode Island, Con- 



