Western Green Drake

Drunella doddsii

Introduction 2

Two species - Drunella grandis and Drunella doddsi - are both also known as green drakes, or western green drakes.

Key Identification Characters - nymph 2

  1. D. grandis: Body shape rectangular and robust with well developed paired spine-like tubercles on top of head and abdominal segments 2-9.
    D. doddsi: Body less rectangular and more oval in shape, no tubercles. Underside of abdomen with obvious pad of fine hairs.

  2. Three tails.
  3. Body length of mature nymphs (excluding tails) 12-16mm.
  4. Body color brown or dark olive to almost black.

Similar nymphs: 2

The size and overall shape of D. grandis and D. doddsi make them quite distinct. Small and immature D. doddsi nymphs could be mistaken for PMD nymphs, but the obvious pad of fine hairs on the underside of the abdomen is unique to D. doddsi. The large tubercles on the head and abdomen of D. grandis help distinguish this species from other Ephemerellidae.

Key Identification Characters - adult: 2

  1. Three tails.
  2. Large robust body from bright green to olive-brown with yellowish segment bands on abdomen.
  3. Hind wings with distinct rounded costal angulation (hump on leading edge).
  4. Wing color pale gray to dark gray (duns), clear (spinners).
  5. Body length 12-16mm.

Similar Winged Mayflies: 2

If you see a large robust mayfly with a green to olive-brown body, large dark gray wings, and three tails, there is little doubt you are looking at either D. grandis or D. doddsi. These two species look quite different as nymphs, but the duns and spinners will be next to impossible to separate without a microscope and good key. If duns or spinners are collected, check for nymphs or their empty shucks. They can help determine which adult you collected. Two smaller species - Drunella flavilinea and D. coloradensis duns- look very similar to Green Drake duns, but are clearly smaller (7-12mm) and slightly darker in color.

Habitat & Distribution 2

Green Drake nymphs occur in a variety of stream types and sizes, but almost always in riffles or runs with moderate to fast currents and large rock substrate. Unlike PMDs that are widely distributed and abundant throughout the West, Green Drakes, while widely distributed, will occur in large numbers in one stream but be quite sparse in another stream nearby.
In Oregon the distribution of Green Drakes is similarly spotty. They occur widely throughout the State, but their abundance varies considerably from one stream to another or even in different sections of the same stream. The Metolius River for example, has a large population of Green Drakes from Wizard Falls hatchery downstream, but above that area they are rare or absent.

Life Cycle - Emergence: 2

Dun emergence occurs in the surface film or a short distance below it, usually from mid-morning to mid-afternoon. Duns escaping the nymphal shuck underwater rise to the surface and break through the surface film and then ride the surface until their wings are functional. After molting to the spinner stage, spinners mate in the air, and then lay their eggs. Good spinner falls can occur from early to mid morning or late afternoon to evening depending on weather conditions.
Green Drakes are univoltine (one generation per year), and emergence can spread out over over a two to four week period.
Oregon Emergence Period: mid May - late June

Metolius: Good emergence from mid May - mid June
McKenzie: Spotty emergence, mostly on the upper river, from late May to late June.
Necanicum/Nehalem: Spotty emergence from late May to end of June?

Sources and Credits

  1. (c) Jerry Schoen, all rights reserved, uploaded by Jerry Schoen
  2. (c) Jerry Schoen, some rights reserved (CC BY-SA)

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