LIFE HISTORY OF BLACKFLIES 



479 



an inch) in length and the largest of them scarcely exceed one- 

 fifth of an inch. 



Life History. Unlike the mosquitoes and midges, blackflies 

 breed in running water and few streams flow too swiftly for 

 them. The eggs are laid in large masses, up to many thousands 

 in number, by a number of 

 females. The eggs (Fig. 221A), 

 which are elliptical and yellowish 

 and have a peculiar slimy coat- 

 ing, are deposited by some spe- 

 cies on leaves or blades of grass 

 which are occasionally licked by 

 running water, the weight of 

 the eggs sufficing to submerge 

 them; other species dart into 

 the water and deposit directly 

 on the slimy surfaces of sub- 

 merged stones or twigs. The 

 author found a favorite breed- 

 ing place of the blackflies in 

 the woods of Northern Ontario 

 (species undetermined) to be on 

 the slimy boards of old lumber 

 chutes over which water was 

 constantly flowing. It requires 



at least a Week for the eggS to FIG. 221. Developmental stages of 



hatch blackflies. A, egg of Simulium venu- 



_ . _ . stum; B, larva of S. bracteatum; C, pupa 



The larva (Fig. 22 IB) as SOOn ( m pup al case) of S. venustum; all much 



as hatched attaches itself by a enlarged, not drawn to same scale; 



an. g., anal gills; ant., antenna; dev. g. 



SUCker at the posterior end OI the fil M developing gill filaments of pupa; 



body to a stone or other sub- 

 merged object. As expressed 

 by Alcock, " one of the most 

 characteristic attitudes of the 

 larva is to sit upright on the end of its tail, to use the lan- 

 guage of the poets of the daily press, with its mouth fans 

 standing out from its head like a pair of shaggy ears." The 

 " mouth fans," which are very delicate and elegant, are used 

 for sweeping microscopic particles into the mouth as they are 

 brought by the running water. The stump of a leg on the 



g. fil., gill filaments; m. f., mouth fans; 

 p. c., wallpocket-like pupal case; post. 

 s., posterior sucker. (A, after Meczni- 

 kow from Jobbins-Pomeroy, others 

 after Jobbins-Pomeroy.) 



