DIPTERA 



303 



antennas (Fig. 522). The antennas are rarely longer than the head and 

 thorax, and composed of short, broad, and closely-pressed-together seg- 

 ments (Fig. 523). 



The adult flies are generally black 

 and red, sometimes yellow or wholly 

 black. They are most common in early 

 spring; which has suggested the name 

 March-flies ; but some occur later in the 

 season, and even in the autumn. 



The larvae vary in habits; some species feed on 

 decaying matter, while others attack the roots of growing plants, especially 

 of grass. They have ten pairs of spiracles, which is a rather large number, 

 although there are other insects that have as many. The pupae are usually 

 free. 



The subfamily, Scatopsince, includes a few species of minute black 

 flies which are from -^ to -^s oi an inch in length. Most of the known 

 larvae live in excrement. 



Fig. 523. — Antenna 

 of Bibio. 



Fig. 522. — Bibio. 



Family Simuliid^e 



The Black-flies 



The common name, black-flies, given to the members of this family is 

 not distinctive, for there are many species of other families that are of 

 this color. It is like the word blackberry; some blackberries are white, 

 and not all berries that are black are blackberries. 



In this family the body is short and stout ; the thorax is much arched, 

 giving the fly a humpbacked appearance (Fig. 524); and the legs are 

 comparatively short. The antennae are scarcely longer than the head and 

 are eleven- jointed ; the segments are short and closely pressed together 

 (Fig. 525); they are clothed with fine hairs. The ocelli are absent. In 

 the male the eyes are very large and contiguous, and divided; the upper 

 half of each has the facets very much larger than the lower, from which 



they are distinctly divided by a 

 horizontal line. In the female, the 

 eye facets are of almost uniform 

 size ; and the two eyes are widely 

 separated. 



The larvae are aquatic; and 

 usually live in swiftly-flowing 

 streams, clinging to the surface of 

 rocks in rapids or on the brinks of 

 falls. They sometimes occur in 

 such large numbers as to form a moss-like coating over the rocks. 

 There is a disk-like sucker fringed with little hooks at the caudal end 

 of the body by means of which the larva clings to the rocks; and 

 just back of the head there is a fleshy proleg which ends in a similar 

 sucker fringed with hooks (Fig. 526). Respiration is accomplished 

 by means of blood-gills. The head bears two large fan-shaped organs, 

 which aid in procuring food. The food consists chiefly of algae and dia- 

 toms. 



When full-grown the larva spins a cocoon within which the pupal 



Fig. 324. — Sitnu- 

 lium. 



Fig. 525. 



Fig. 526. — Head 

 of larva. 



