The Black Flies and Buffalo Gnats 



which the following account is condensed. The adults occur in 

 the early part of May or at the beginning of the first continuous 

 warm we.ither in the spring. The eggs are deposited on rocks 

 over which the water is flowing. The flies hover in little swarms 

 a foot or two above the rock, rapidly flying back and forth, and 

 occasionally darting down and depositing their eggs beneath 

 the water on. the flat surface of the rock. The batch of eggs 

 becomes at least a foot or more in diameter and is distinctly 

 observable at some distance on account of the light yellowish 

 color. When the water is very shallow and its velocity slight 

 the flies sometimes crawl over the surface of the rock and deposit 

 eggs without flying. Only a small proportion of the eggs pro- 

 duce larvae. The larvae hatch about eight days after the eggs are 



laid and in this stage the in- 

 sect may be found at any 

 season of the year, in summer 

 as well as in winter, and it is 

 in this stage that it hibernates. 

 The larvae die in three or four 

 hours when placed in quiet 

 water. Fastened to the rock 

 by the anal end of the body 

 they assume an erect position 

 and move the head around 



Fig. 72. Simulium invenustum, female. Occasionally with a circling 

 (From U. S. Dept. Agr.) motion. 



They may release themselves and as they grow larger they 

 sometimes allow themselves to be washed into deeper water, 

 holding by a thread which they spin as they go. The thread is 

 spun from the mouth but is attached along the side of the body 

 to the different segments. Sometimes a large cluster of larvae 

 will cling to the same thread which they can ascend in much the 

 same manner as do spiders. Not much food is taken in the 

 winter time. During the summer the length of the larval life is 

 about four weeks, varying with the temperature and the velocity 

 of the water. When full grown the larva spins its cocoon, firmly 

 attaching it to the rock and also to adjacent cocoons. The length 

 of the pupal stage is about three weeks. Over-wintering larvae 

 transform to pupae about the I2th of April, the first flies appearing 

 on the 2d of May. The newly issuing fly surrounded by a 



