Mayfly Species Rhithrogena amica

A medium-sized species of the Rhithrogena anomala group; cross veins mainly brown, tails dark smoky brown.

Frontal portion of head greyish brown, vertex and median carina red-brown. Black semi-circular mark at base of antenna; fine dark hair-line between antenna and ocellus, from corner of eye. Bases of antennae pale; filament dusky, tip pale. Thoracic notum dark reddish brown; pronotum with darker shading laterally. Mesonotum may be yellow-tinged laterally. Pale spot anterior to scutellum; scutellum and all posterior portions of mesonotum blackish brown. Pleura paler than notum, more yellowish, with red-brown areas; purplish grey streak anterior to wing roots, purplish markings above and anterior to coxae. Sternum light red-brown, posterior portion of mesosternum deep red-brown. Fore legs olive brown, femur with reddish tinge; apex of femur and tibia blackish brown. Middle and hind legs yellowish; femora with reddish tinge; tarsi and apices of femora smoky brown. All femora with blackish spot at center, and usually with fine black longitudinal hair-line from base to apex. Small black spot at apex of each trochanter. Wings hyaline; basal half of fore wing may have very faint brownish tinge. Venation pale red-brown; basal costal and all of subcostal cross veins so faint as to be almost invisible; humeral cross vein red-brown, pale at costal margin. Stigmatic area opaque whitish.

Abdominal tergites dark red-brown, 2-7 with purplish tinge; apical tergites brighter red-brown, less tinged with purple; lateral margins of 9 and 10 largely yellowish. Posterior margins narrowly darker brown; pleural fold slightly paler. Traces of pale mid-dorsal line and of short submedian streaks near center of each basal and intermediate tergite; pale marks at anterior and lateral margins (prominent in R. anomala), either absent or very faint. Sternites pale red-brown, more yellowish apically, usually semi-hyaline; sternite 9 yellow, outlined narrowly in dark brown. Genitalia red-brown, including forceps base; penes very similar to R. anomala, buts slightly less outcurved at tips (see fig. 101). Tails dark olive to smoky brown, joinings narrowly darker.

Female very similar to male; head and thorax largely greenish-olive brown. Nymph blackish red-brown dorsally. Gills pale greyish. Central portion of basal and middle areas of each femur largely occupied by a large pale somewhat cross-shaped mark. Tails red-brown. This species is slightly larger and darker than the closely-allied R. anomala, and with less of a reddish tinge; the darker tails and brown cross veins also serve to distinguish it from that species. It is distinctly larger and darker than Rhithrogena fasciata, which is also a member of this group.