June, 1912.] AlDRICH : BlOLOGY OF WESTERN EpHYDRA. 83 



The shores of the lake everywhere are more or less covered with 

 windrows of puparia, which frequently form dark ridges that can be 

 seen for a long distance. One of my half-tones (PI. VIII, Fig. 8) 

 shows the little bay on the north side, where the cutoff reaches the 

 Point from the east. Here considerable drift accumulates, and the 

 fly puparia form a mass filling the water close to shore, and a foot 

 or more deep above the water for some distance ; all the dark color 

 in the water and along the edge is simply a collection of millions of 

 puparia. The other half-tone of this subject is PI. VIII, Fig. 9, which 

 shows the shore on the south side of the railroad looking west. Here 

 also the broad dark margin of the water is composed of puparia. 

 Fig. 3 shows a small cluster of puparia held together by the diverging 

 branches of the anal tubes. Fig. 4 is a small mass of puparia taken 

 from a dry windrow on the beach near Garfield in 1908. 



Adults. — The adults are found on the surface of the water all 

 over the lake, but along the beaches they gather in large numbers, 

 probably because they emerge there from the windrows of puparia 

 that wash up. On July 31, 1908, I visited the shore near Garfield, 

 at the south end of the lake. Near the rocks which come down to 

 the edge of the water at the county line, I waded in and investigated 

 the flies. At that time the surface of the water from the shore out 

 for a distance of about eighteen feet was perfectly covered with the 

 adult flies. They made a black belt along the beach that was visible 

 for several miles, or as far as the shore line could be seen. They 

 were crowded closely together, and when disturbed by my near 

 approach they would rise only a few inches and immediately settle 

 again. They extended up the beach a few feet above the water also, 

 so the average width of the mass was over 20 feet. I thought that 

 there were more than 25 flies to the square inch ; in fact, double that 

 seems a small estimate. The minimum estimate would give about 

 370,000,000 flies to the mile of beach. 



In bathing at Saltair, I heard one bather say to his companion, 

 '' Don't go near those piles, you'll get covered with gnats." This was 

 in allusion to E. gracilis, which I found on examination was present 

 in large numbers, but as I could see it on the surface of the water 

 everywhere it did not seem especially bad about the piles. There 

 is occasional complaint about " gnats " by the bathers, but the flies 



