Epeorus pleuralis

Adult: Adults of the genus Epeorus are identified by their flat bodies, lack of any transverse suture (= a horizontal line dividing the top view of the thorax into an anterior portion and the posterior portion) on the thorax (= the mid-section between the wings), broad hindwings without dark markings at the farthest ends, and presence of two distinct tails (also in the genus Ironodes but all other mayflies have three). All Epeorus adults also possess heart-shaped femoral (= third leg segment; the part closest to the body) markings. Legs are otherwise dark brown. E. pleuralis is generally dark brown but paler beneath. Males have crystalline forewings with dark brown veins and a faint hue of sepia at the margins. The head is reddish-brown with darker embellishments and eyes are darker brown and large. There is a faint scarlet color at the roots of the antennae. The pronotum (= space between the eyes) is nearly as long as it is broad and is colored dark reddish-brown with front and sides straight but hind margin convex and angles obtuse. The dorsal surface of the abdomen is medium brown in the middle with occasional pale areas laterally (without any black marks). Total length: 1.18-1.97 inches (30-50 mm); forewing: 0.28-0.51 inches (7-13 mm).|Similar Species: The E. pleuralis species group includes E. fragilis, E. frisoni, E. namatus, and E. pleuralis. Differentiating these should only be attempted by experienced observers. Wings are usually swept backwards at a rakish angle unlike the upright wings of other early emerging mayflies like Ephemerella subvaria. The abdomen of the E. vitreus group has black markings on the posterior margins of the tail. On E. frisoni, the otherwise white tail has faint yellowish shading over the last one third and the genitals have hook-like projections (at the tip of the tail) extending upwards. E. fragilis is very similar but is smaller (generally < 0.27 inches, or < 6.8 mm) with the top surface of the tail pale yellowish-brown or pale yellowish-white and having faint dark brown on the posterior margin (unlike E. pleuralis which has a mostly medium brown tail with paler areas laterally).|Nymph: Nymphs of Epeorus are identified by their flat bodies and distinct two tails (also in the genus Ironodes, but all other mayflies have three). Epeorus nymphs also possess heart-shaped femoral (= third leg segment; the part closest to the body) markings, large, plate-like gills along the sides of the abdomen, and a dense row of hairs on the front margin of the head. The larva is a dark olive-brown and almost flat, with eyes set on top of the head. Wing pads are dark brown and legs mottled olive-brown. Large, light gray, overlapping plate-like gills extend along the sides. Nymphs have gills on abdominal segments 1 and 2. The first pair of abdominal gills is greatly enlarged and generally extends fully under the body and meet in the middle. Total length: 0.35-0.51 inches (9.00-13.00 mm) but generally > 0.39 inches (9.85 mm) (males larger than females).|Similar Species: The pleuralis species group includes Epeorus fragilis, Epeorus frisoni, Epeorus namatus, and Epeorus pleuralis. Differentiating these should only be attempted by experienced observers. Larvae of the pleuralis species group are generally characterized by having the lamellae (= gill filaments) of gill 1 greatly enlarged anteriorly, whereas the first gill of the vitreus species group are not enlarged and look similar to the remaining gills. The E. vitreus group has paired spots marked along the upper surface of the abdomen that the E. pleuralis group lacks. Also, the third segment (i.e. the one closest to the body) of each leg is blunt where it connects to the second segment as opposed to sharp as in the E. vitreus group.

This species ranges from the Appalachians of Georgia and South Carolina to the Maritime Provinces of eastern Canada and as a glacial relict as far west as Indiana.

Quill gordon nymphs have an unusual habit of gathering en masse on the downstream side of certain objects in the stream prior to emergence. It is a cool water species found in fast flowing water with gravel bottoms and is restricted in the southern portions of its range to cooler environments such as cold mountain streams and spring-fed brooks.

The quill gordon spends most of its one-year life cycle in larval form before the nymphs hatch and rise to the surface as fully formed adults ready to fly. Once the hatch is triggered by several consecutive days of ideal water temperature, it carries a sort of momentum. The subimagos (= dun, or stage that emerges from the water) complete transformation underwater, on the stream bottom, unlike most mayflies. The entire process takes about 1-2 hours. They continue to hatch almost every day, regardless of weather, until they are all done. After emerging, the subimagos may ride the surface for a long time and make several attempts at flight before getting airborne. The quill gordon is one of the earliest mayflies to emerge in eastern streams. Emergence time depends on water temperature. It occurs in central Appalachian streams in early April and moves into southern Pennsylvania in mid-April. By early May it is going strong in the Catskills, and it lingers through the rest of May in the Adirondacks and New England. Emergence time is generally early March to early June in Kentucky, mid-April to mid-May in Michigan and Wisconsin, throughout all of May in Great Lakes drainages as well as New England and the Adirondacks, late April to early June in Maine, extending to mid-June in the cooler Catskills, mid-April to mid-August in Ontario, late March to late April in New Jersey.