222 American Midland Naturalist Monograph No. 3 



a prominent tubercle; claspette filament (Cl-F) about three-fourths as long as 

 stem, slender, sickle-shaped. Basis tyle (Bs) about three and one-half times as 

 long as broad, nearly straight, conical, narrowly rounded at apex, clothed with 

 long and short setae and numerous large scales; basal lobe (B-L) inconspicu- 

 ous, represented by a small slightly raised darkly pigmented area covered by a 

 dense patch of setae; apical lobe absent. Diitistyle (Ds) about two-thirds as 

 long as basistyle, evenly curved, not expanded medially, glabrous except for a 

 few setae near apex; terminal claw (Ds-C) slender, about one-fifth as long as 

 basistyle. 



LARVA. (Fig. 122). — Head slightly broader than long. Antenna less than 

 half as long as head, slightly curved, spinose; antennal tuft small, 2 to 3- 

 branched, inserted at middle of shaft. Head hairs: Preantennal (A) 3 to 4- 

 branched; lower (B) and upper (C) single; postclypeal (d) small, usually 

 2 to 3-branched; sutural (e), trans-sutural (f), and supraorbital single. Comb 

 of eighth segment of many scales in a patch; individual scale fringed apically 

 with subequal spinules. Siphon slightly less than twice as long as wide; pecten 

 of numerous teeth extending nearly to tip of siphon, the last 3 or 4 teeth 

 widely spaced; subventral tuft multiple, barbed, inserted within the pecten. 

 Anal segment about as long as wide, with the dorsal plate extending halfway 

 down the sides; lateral hair single or double; dorsal brush consisting of a long 

 lower caudal hair and a shorter multiple upper caudal tuft on either side; 

 ventral brush well-developed, confined to the barred area; gills 4, about three 

 times as long as the anal segment. 



DISTRIBUTION. — Southern Canada; United States; Mexico (87); and 

 Central America (54). Southern States: Arkansas (30); Missouri (70); 

 North Carolina (166); Tennessee (170); Virginia (52). Other States: Ari- 

 zona, Connecticut and District of Columbia (52); Maine (137); Maryland 

 and Massachusetts (52); Minnesota (131); New Hampshire (52); New Jer- 

 sey (77); New Mexico and New York (52); Oklahoma (159); Pennsylvania 

 (52); Rhode Island (99); Texas (108) ; Vermont (90); Wisconsin (48). 



BIONOMICS. — The females of A. atropalpus are active biters and frequently 

 annoying near rocky streams along which they breed. Carpenter (30) found 

 adults, both males and females, resting during the daytime under rock ledges 

 near their breeding places on Petit Jean Mountain in Arkansas in 1938, and 

 several females were taken biting during daylight hours in the same area. Owen 

 (131) states that females of this species feed freely on man in Minnesota 

 when encountered but were never observed far away from their breeding places. 

 Owing to the limited number of suitable breeding places, the species is never 

 extremely abundant and only troublesome locally. 



The larvae are usually found throughout the summer in overflow pools in 

 rock holes along mountain streams, but may also be taken on occasions in rain- 

 filled depressions in rocks some distance from such streams. Although the 

 larvae are slow in development, the species is several-brooded in warmer cli- 

 mates. The eggs are laid singly above the water level and are apparently firmly 

 attached to the rock so as to withstand winter floods. Larvae were collected 



