Mayfly Species Stenacron gildersleevei (Light Cahills)

A large species of interpunctatum group (now a synonym of Stenacron interpunctatum); abdominal tergites largely purplish black; fore tarsus shorter than or about as long as tibia, basal joint almost 1/2 of second.

Head reddish yellow; usually a continuous black transverse stripe across face below antenna, from inner corner of eye (in one paratype, no continuous stripe, but black dash below antenna, black spot on carina). Antennal filament dusky, tip paler. A black spot on each side of vertex; a small reddish median spot; dark shading along median line and posterior margin. Pronotum largely purplish black in median area, including posterior margin; lateral areas yellowish, margined laterally and posteriorly with faint dusky lines; a wide black oblique mark on each side. A short black transverse streak at base of fore coxa. Mesonotum reddish brown; a darker median stripe, distinctly purplish black in anterior and posterior portions, including scutellum; antero-lateral and postero-lateral margins of mesonotum, and a median black triangle occupying most of metanotum, also blackish; above root of hind wing, a rather large yellow spot. Pleura yellowish, tinged with reddish brown; purplish black markings above leg bases and anterior and posterior to middle and hind coxae; no prominent oblique streaks anterior to legs, as in S. canadense (now a synonym for Stenacron interpunctatum). Sternum yellowish.

Legs yellowish; femora deeper yellow; tarsi often tinged with smoky. Wide median and apical purplish black bands on all femora (may be fainter on hind leg). Apex of fore tibia blackish; apical portion of each tarsal joint deeper smoky; apices of middle and hind tibiae, and tarsal joinings, narrowly dark brown; distal tarsal joints deep smoky apically. Basal fore tarsal joint almost 1/2 the length of the second; in one specimen, however, as short as in S. canadense (now a synonym of Stenacron interpunctatum). Fore tarsus relatively short, usually about as long as tibia (may be slightly shorter). Wings hyaline, but with faint milky tinge. Longitudinal veins of costal margin yellowish, others amber to light reddish brown. Cross veins purplish black; those of basal costal border narrowly margined as usual; at bulla, 2 or 3 in radial space connected by a black dash. A faint brownish stain in stigmatic area, extending around tip of wing. Veins in anal region of fore wing, and in posterior half of hind wing, finer and paler; outer margin of hind wing narrowly dusky.

Abdominal segments 1-6 and base of 7, semi-hyaline, pale yellowish white; tergites largely occupied by a wide median purplish black area, leaving only the lateral areas and very narrow submedian streaks pale. Posterior margins and mid-dorsal line deeper in color; diffuse spiracular marks are present, but often fused with the dark median area so as to be indistinct. A purplish black transverse streak on each side of mid-ventral line of basal and middle sternites, on posterior margin; on basal segments, a diffuse purplish grey triangle extends backward obliquely from this dark streak. Segments 8-10, and apical portion of 7, opaque, deep yellow, tergites often shaded with reddish brown; posterior margins and median line on 8 and 9 blackish, with faint lateral shading; 10 pale except for faint median and submedian streaks and a narrow dark mark on posterior margin at median line. Genitalia yellowish to pale reddish brown; penes much as in S. frontale (now a synonym of Stenacron interpunctatum). Tails pale yellowish; joinings opaque; on some specimens, basal joinings faintly brownish. Female larger than male, somewhat paler, but with same dark markings; abdominal tergites deep red-brown. Dorsal view of abdomen of nymph shown in fig. 92. This species is very similar to S. canadense (now a synonym of Stenacron interpunctatum) in the imago stage; apparently distinguished by the relatively shorter fore tarsus with slightly longer basal joint; lack of prominent dark oblique streaks on pleura; paler tails with less conspicuous joinings; more definite mid-ventral markings. The size is slightly larger; the penes show slight differences. Distinguished from ohioense (now a synonym of Stenacron interpunctatum) as indicated under that species.