Blog & Latest Updates
Fly Fishing Articles
Insects by Common Name

Trout Streams & Rivers
Trout Pictures
Underwater Pictures

Desktop Backgrounds
Stream & Bug Videos
Image Use Pricing

Chocolate Duns

Mayflies

Caddisflies

Stoneflies

Scientific Names

Match	Scientific Name
	Eurylophella
	Eurylophella bicolor
	Ephemerella needhami
	Ephemera simulans

Like most common names, "Chocolate Dun" can refer to more than one taxon. They're previewed below, along with 8 specimens. For more detail click through to the scientific names.

Mayfly Genus Eurylophella

These are often called Chocolate Duns.

None of the species in this genus are recognized as significant hatches. Nevertheless, I have found their nymphs in my samples in many streams in both the East and Midwest.

Eurylophella temporalis (Chocolate Dun) Mayfly Nymph

View 9 Pictures

Collected June 5, 2005 from in
Added to Troutnut.com by on May 25, 2006

Male Eurylophella (Chocolate Duns) Mayfly Dun

View 5 Pictures

Collected June 14, 2005 from in
Added to Troutnut.com by on May 26, 2006

Male Eurylophella (Chocolate Duns) Mayfly Spinner

View 10 Pictures

Collected June 4, 2005 from in
Added to Troutnut.com by on May 24, 2006

See 19 more specimens...

Mayfly Species Eurylophella bicolor

These are often called Chocolate Duns.

According to the Leonards in Mayflies: An Angler's Study of Trout Water Ephemeroptera , this species and Eurylophella bicolor are the two most likely hatches for fly fishermen to encounter in Michigan. Based on my sampling, it seems other species may be more prevalent elsewhere.

Mayfly Species Ephemerella needhami

These are very rarely called Chocolate Duns.

This small and slightly noteworthy mayfly appears during the finest hours of the year. Ernest Schwiebert describes an Ephemerella needhami day in Matching the Hatch:

"It was a wonderul morning, with a sky of indescribable blue and big, clean-looking cumulus clouds, and the water was sparkling and alive. You have seen the water with that lively look; you have also seen it dead and uninviting in a way that dampens the enthusiasm the moment you wade out into the current."

I have not fished a needhami emergence, but the exquisite nymphs show up often (though never abundantly) in my samples.

Ephemerella needhami (Little Dark Hendrickson) Mayfly Nymph

View 6 PicturesI photographed three strange striped Ephemerella nymphs from the same trip on the same river: this one, a brown one, and a very very striped one. I have tentatively put them all in Ephemerella needhami for now.

Collected June 9, 2005 from in
Added to Troutnut.com by on May 26, 2006

Ephemerella needhami (Little Dark Hendrickson) Mayfly Dun

View 7 PicturesSee the comments for an interesting discussion of the identification of this dun.

Collected June 1, 2007 from in
Added to Troutnut.com by on June 4, 2007

See 7 more specimens...

Mayfly Species Ephemera simulans

These are very rarely called Chocolate Duns.

The Brown Drakes are a favorite hatch of many in the Midwest, and they make a good showing on localized waters across the country. They are usually the first in a series of big drakes which bring large trout to the surface at twilight and into the early hours of the night.

Ephemera simulans (Brown Drake) Mayfly Nymph

View 10 Pictures

Collected January 31, 2004 from in
Added to Troutnut.com by on January 25, 2006

Male Ephemera simulans (Brown Drake) Mayfly Dun

View 2 Pictures

Collected July 11, 2009 from in
Added to Troutnut.com by on June 27, 2011

Male Ephemera simulans (Brown Drake) Mayfly Spinner

View 7 Pictures

Collected June 2, 2005 from in
Added to Troutnut.com by on May 24, 2006

See 12 more specimens...

Jargon Defined:

Dun: Mayflies have two adult stages. They first emerge from the water as duns (scientifically known as the subimago stage). They then molt into the spinner (imago) stage, in which they mate and die. Sometimes the word "dun" is confusingly used to refer to a brownish gray color in fly tying materials.

Emergence: The transformation of a nymph or pupa into the adult winged stage of an insect. The term may refer to the emergence of an individual, or the daily or yearly event in which all individuals of a species emerge.

Nymphs: The juvenile, underwater stages of mayflies, stoneflies, dragonflies, and damselflies and other aquatic insects whose juvenile stages are covered by hard exoskeletons. The word can also refer to the fishing flies which imitate these creatures, in which case it is used as a blanket term for flies imitating any underwater stage of an invertebrate (except for crayfish and leeches).

Useful References:

Knopp, Malcolm and Robert Cormier. 1997. Mayflies: An Angler's Study of Trout Water Ephemeroptera . The Lyons Press.

Schwiebert, Ernest G. 1955. Matching the Hatch. MacMillan Publishing Company.