The eggs are deposited in a compact yellowish layer on the surface of rock, on the brinks of falls and rapids where the water is flowing swiftly. They are elongate ellipsoidal in shape, about .4 by .18 mm. As myriads of females deposit in the same place the egg patches may be conspicuous coatings of a foot or much more in diameter. When first laid they are enveloped in a yellowish white slime, which becomes darker, until finally it becomes black just before the emerging of the larvæ. The egg stage lasts a week. The larvæ (fig. 75) are black, soft skinned, somewhat cylindrical in shape, enlarged at both ends and attenuated in the middle. The posterior half is much stouter than the anterior part and almost club-shaped. The head bears two large fan-shaped organs which aid in procuring food. Respiration is accomplished by means of three so-called blood gills which are pushed out from the dorsal part of the rectum. The larvæ occur in enormous numbers, in moss-like patches. If removed from their natural habitat and placed in quiet water they die within three or four hours. Fastened to the rock by means of a disk-like sucker at the caudal end of the body, they ordinarily assume an erect position. They move about on the surface of the rocks, to a limited extent, with a looping gait similar to that of a measuring worm, and a web is secreted which prevents their being washed away by the swiftly flowing water. They feed chiefly upon algæ and diatoms. The complete larval stage during the summer months occupies about four weeks, varying somewhat with the temperature and velocity of the water. At the end of this period they spin from cephalic glands, boot-shaped silken cocoons within which they pupate. The cocoon when spun is firmly attached to the rock and also to adjacent cocoons. Clustered continuously over a large area and sometimes one above another, they form a compact, carpet-like covering on the rocks, the reddish-brown color of which is easily distinguishable from the jet-black appearance of the larvæ. The pupal stage lasts about three weeks. The adult fly, surrounded by a bubble of air, quickly rises to the surface of the water and escapes. The adults (fig. 76) are apparently short lived and thus the entire life cycle, from egg to egg is completed in approximately eight weeks. [Illustration: 76. Simulium venustum, (×8). After Garman.] In the case of _Simulium pictipes_ at Ithaca, N. Y., the first brood of adults emerges early in May and successive generations are produced throughout the summer and early autumn. This species winters in the larval condition. Most of the other species of _Simulium_ which have been studied seem to be single brooded.