Mayfly Species Hexagenia atrocaudata (Late Hexes)

A large dark species; abdomen blackish brown with olivaceous areas; outer margin of hind wing widely purplish brown; penes short, broad, bluntly pointed.

Head light red-brown; carina and frontal margin pale, vertex yellow. Eyes deep orange; very large, almost contiguous above. Pronotum blackish, median and lateral areas paler. Mesonota and metanota and pleura dark reddish to olive brown; a paler reddish median streak on mesonotum; yellowish markings on pleura below wing roots, above leg bases. Sternum deep reddish to purplish brown. Fore legs deep reddish black, middle tarsal joints a pale yellowish basally. Middle and hind legs greenish yellow; distal tarsal joint, tarsal joinings and claws purplish black. Wings hyaline; all veins blackish. Costal margin of fore wing “heavily tinged with brown in the apical half and between veins 2 and 3 in the basal half” (McDunnough). Cross veins in costo-apical space tend to anastomose; only & few cross veins in either wing are narrowly dark-margined, no conspicuous dark spots. Outer margin of hind wing with a very wide purplish black border.

Abdominal tergites dark blackish brown; 1 and 2 largely dark, only a narrow paler median line. Median yellowish olive triangular areas, widened posteriorly, on tergites 3-6; on 7 and 8, a pale median streak at anterior margin only. Pale antero-lateral triangles on tergites 3-10, separated from pale postero-lateral triangles by the blackish-brown lateral stripes, on the middle tergites. “The triangular dorsal portion of segment 10 is dull brown, edged with black and with geminate black medio-dorsal streaks” (McD.). Median triangles on sternites dark brown, the base of each extending over most of the posterior margin of the sternite; the apices attain the anterior margins. A small dark spot in the antero-lateral angle of each sternite, so that only Iateral triangles of the pale olivaceous yellow background remain. Near center of each sternite are two small pale dots, one on each side. Genitalia largely dark red-brown, with a few yellow markings; penes distinctive, being broad, short and bluntly pointed (see fig. 84). Tail joints blackish brown, each with a narrow yellow basal ring. See frontispiece. The characteristic genitalia separate this species from all others in the genus.