46 
current of the stream. * * * * When frightened they 
drop into the water, suspended to the substance to which they had 
been attached by means of a fine delicate thread, in a similar man¬ 
ner to many land larvae. They can ascend this thread, but it is 
very easily broken by the action of the water. * * * * 
Fig. 21. The Black-fly, Simulium venustum , pupa and cocoon, lateral and dorsal aspects 
A, adult emerging. (From H. Garman.) 
The pupae, as well as larvae, perish in water of a temperature 
warmer than that of the stream. * * * * I was en¬ 
abled to obtain the perfect insect by keeping pupae in a covered 
box in the current of the stream. A day or two previous to emerg¬ 
ing from the water, the pupa loosens itself from the case or 
“pouch” by a gentle wriggling motion from side to side. When 
it becomes free it rises to the surface of the water, and the fly 
gradually draws itself out of a slit the entire length of the pupa. 
The legs are the last to appear. The fly rests on the surface of 
the water until its wings expand and dry. This process usually 
takes a minute of time—sometimes more or less. Thev leave the 
j 
water just before sunset, and will then be found flying among 
low herbage near the bank of the stream. * * * There 
have been a succession of broods this summer. During the wann 
season, a period of two months elapses between the egg and per¬ 
fect forms. They were a week or ten days as eggs, four weeks 
as larvae, and about three weeks as pupae. * * * At the 
present time (Oct. 18th) there are large quantities of minute 
larvae on the leaves of the water-cress.” 
Fig. 22. The Bluck-fly. Simulium venustum, pupa, three-quarters’ view 
X 15. 
