Hendrickson
Ephemerella subvaria
DUN (SUBIMAGO) 10
Size: Body size: 8-12 mm (males slightly smaller than females)
Body: Grey-brown to tan-brown; females generally lighter than males
Wings: Large hind wings; uniform medium grey
Tails: Three tails (all same size)
Dun/Spinner Look Alikes 10
Quill Gordons (Epeorus pleuralis), while slightly smaller and daintier, resemble E. subvaria duns and spinners. They can readily be distinguished from one another by the number of tails (only two on the former). Hendrickson adults may also be confused with those of the genus Leptophlebia (the Black Quill), which is also an early season hatch (but far less often encountered than the Hendrickson). The Black Quill can be distinguished from the Hendrickson by the presence of a middle tail that is noticeably shorter than the outer filaments. Also note the distinct wing venation on the Black Quill that is not evident on the Hendrickson.
HABITAT & DISTRIBUTION 10
Ephemerella subvaria is a common, often abundant, mayfly on many northeastern trout streams. The nymphs inhabit well-oxygenated riffles and runs, from which they emerge in the late spring. The nymphs are said to avoid areas of fluctuating water temperatures.
LIFE CYCLE - EMERGENCE 10
Hendricksons are among the first mayflies to hatch each spring, often following the Quill Gordons (Epeorus pleuralis) by only a few weeks. In central New England, hatching may begin as early as April and go on for several weeks, sometimes into early June, dependent on weather conditions. The nymphs emerge by swimming to the surface where they will writhe to free themselves of their nymphal shuck. Emergers and newly hatched duns may ride on the water’s surface for some distance, making for easy and enticing quarry for feeding trout. Information relating to the behavior and importance of the spinners to the fly angler is conflicting. While most sources suggest that females drop their eggs to the water from high in the air, minimizing their importance as fish food until they drop spent in the later evening, a few sources suggest that the females do lay their eggs while laying on the water.
Massachusetts: April into early June, depending on weather and water temperatures.
NYMPH 10
Size: 8-11 mm.
Body: Rounded in cross section (not flattened); color olive brown, red brown, to black brown, often with lighter band across abdomen.
Legs: Light brown/tan with darker brown banding.
Tails: three tails.
Nymph Look Alikes 10
Ephemerella subvaria nymphs are easily confused with those of Ephemerella invaria (Sulphur or Pale Evening Dun). Only E. subvaria has the distinct banding on the abdomen, but this does not occur on all individuals. E. subvaria nymphs are usually also larger when fully mature.
SPINNER (IMAGO) 10
Size: Body size: 8-12 mm (males slightly smaller than females)
Body: Dark reddish-brown
Wings: Large hind wings; hyaline (clear) wings
Tails: Three tails (all same size)
Distribution 11
occurs (regularly, as a native taxon) in multiple nations
Sources and Credits
- (c) Jerry Schoen, some rights reserved (CC BY-NC-ND), http://www.flickr.com/photos/79718069@N00/7401583612
- (c) Bob Henricks, some rights reserved (CC BY-SA), https://www.flickr.com/photos/aquaticinsects_of_central_virginia/13157656185/
- (c) Jerry Schoen, some rights reserved (CC BY-NC-ND), http://www.flickr.com/photos/79718069@N00/8346835387/
- (c) Bob Henricks, some rights reserved (CC BY-SA), https://www.flickr.com/photos/aquaticinsects_of_central_virginia/13157772543/
- (c) Susan Elliott, some rights reserved (CC BY-NC), uploaded by Susan Elliott
- (c) Stroud Water Research Center, some rights reserved (CC BY), http://www.boldsystems.org/archive/image.php?id=bold.org/272332
- (c) Stroud Water Research Center, some rights reserved (CC BY), http://www.boldsystems.org/archive/image.php?id=bold.org/272493
- (c) Stroud Water Research Center, some rights reserved (CC BY), http://www.boldsystems.org/archive/image.php?id=bold.org/272494
- (c) Stroud Water Research Center, some rights reserved (CC BY), http://www.boldsystems.org/archive/image.php?id=bold.org/599536
- (c) Jerry Schoen, some rights reserved (CC BY-SA), http://www.inaturalist.org/guide_taxa/35362
- (c) NatureServe, some rights reserved (CC BY-NC), http://eol.org/data_objects/28962609
