BIOLOGICAL NOTES ON BLOODSUCKING FLIES 225 



and animals, Sambon considered Simulium as the carrier of pellagra, 

 but his theory has not been substantiated. Jobbins-Pomeroy has given 

 quite a full treatment of the life history of several species of this genus, 

 and Malloch has presented a classification of our American forms. The 

 larvae breed usually in swift-flowing water. 



The eggs are small, rather triangular or ovoid objects, and somewhat 

 yellowish in color after a few days. They are laid in masses on grass 

 blades, or leaves, or on stones and other forms of debris at the surface 

 of the water or under the surface. The egg stage varies in each species 

 according to the temperature, but in Jobbins-Pomeroy's studies of five 



Fig. 43. Larva of a buffalo gnat, Simulmm. (Jobbins-Pomeroy.) 



species, the incubation period ranged from 7 to 13 days. A single female 

 may lay from 500 to 1500 eggs according to published claims. 



The larvae are invariably aquatic, and are quite characteristically 

 marked by the possession of two large appendages on the head in front 

 of the antennae, which are provided with fans of long hairs. These fans 

 serve to brush food particles into the mouth of the larva (fig. 43). 



The mesothorax is provided with a single retractile proleg armed at 

 its apex by a circular row of short booklets or spines. This pseudopod 

 with its sucker is used by the larva in attaching itself to objects. A simi- 

 lar but larger sucker-like disk is situated on the caudal extremity of the 

 larvtT. Respiration takes place through rectal gills located dorsally to 

 the caudal sucker. These gills are retractile into the rectum, but are 



