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Mayfly Species Ephemerella invaria (Sulphur Dun)

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This species, the primary "Sulphur" hatch, stirs many feelings in the angler. There is nostalgia for days when everything clicked and large, selective trout were brought to hand. There is the bewildering memory of towering clouds of spinners which promise great fishing and then vanish back into the aspens as night falls. There is frustration from the maddening selectivity with which trout approach the emerging duns--a vexing challenge that, for some of us, is the source of our excitement when Sulphur time rolls around.

Ephemerella invaria is one of the two species frequently known as Sulphurs (the other is Ephemerella dorothea). There used to be a third, Ephemerella rotunda, but entomologists recently discovered that invaria and rotunda are a single species with an incredible range of individual variation. This variation and the similarity to dorothea make matching this hatch exceptionally tricky.

As the combination of two already prolific species, this has become the most abundant of all mayfly species in Eastern and Midwestern trout streams.  

Where & When


Regions: East, Midwest

Time Of Year (?): May-June

The invaria hatch begins in early May in Pennsylvania. The Catskills peak in late May and early June, while mid-June is best in the Adirondacks and the northern fringe of the Upper Midwest.

Good fishing from this hatch usually lasts about two weeks in a particular location.

Hatching Behavior


Time Of Day (?): Flexible based on weather. Generally mid-afternoon at first and later as the season progresses.

Habitat: Almost anywhere, but best near fast runs and riffles.

Water Temperature: 52-60°F
Ephemerella invaria nymphs drift for some time just below the surface as they begin to emerge, and these floating nymphs cause rises to the surface which may fool the angler into thinking the trout are taking duns.

Emergence itself takes quite a while, making emerger patterns more important for this hatch than for most. This importance is heightened by the lower availability of the fully formed duns. These duns take to the air more quickly than most of their Ephemerella kin, but anglers should still be prepared to imitate them if need be.

Spinner Behavior


Time Of Day: Dusk

Habitat: Riffles
Duns typically molt and return to the water as spinners within one day. The females drop their eggs in mid-air and are not exposed to trout until they fall spent (Spent: The wing position of many aquatic insects when they fall on the water after mating. The wings of both sides lay flat on the water. The word may be used to describe insects with their wings in that position, as well as the position itself.)--if they fall spent (Spent: The wing position of many aquatic insects when they fall on the water after mating. The wings of both sides lay flat on the water. The word may be used to describe insects with their wings in that position, as well as the position itself.) at all.

Knopp & Cormier write in Mayflies: An Angler's Study of Trout Water Ephemeroptera that the males seldom fall spent (Spent: The wing position of many aquatic insects when they fall on the water after mating. The wings of both sides lay flat on the water. The word may be used to describe insects with their wings in that position, as well as the position itself.) on the water and the females only fall sometimes. Ted Fauceglia's Mayflies says both genders fall spent (Spent: The wing position of many aquatic insects when they fall on the water after mating. The wings of both sides lay flat on the water. The word may be used to describe insects with their wings in that position, as well as the position itself.) on the water. This disagreement mirrors the confusion I've felt about this species on the stream; the spinners are generally unpredictable, but they can provide excellent fishing.

Nymph Biology


Current Speed: Usually medium to fast, sometimes slow

Substrate: Many types, but gravel is preferred

Environmental Tolerance: Unlike Ephemerella subvaria, invaria is very tolerant of a wide range of conditions.

These are among the most adaptable of mayflies, thriving in many types of habitat. They inhabit warmwater streams as well as cold and are found up and down the channel in riffles, pools, and runs. They are most prolific in deep, gravel-bottomed riffles.

In the days and hours before the hatch these nymphs become especially active, so their imitation is especially useful. They clamber to better emergence sites where they rest in plain view of both trout and photographers (see my underwater photos). They also make apparent "practice runs" to and from the surface in the manner of Ephemerella subvaria.

The nymphs are a little bit difficult to recognize because they their base color ranges from brown to olive and they're adorned with many possible color patterns. Anglers should be prepared with imitations in brown and olive, hook sizes 12 through 16.

Ephemerella invaria Fly Fishing Tips


Take extra care during emergence to figure out if the trout are feeding on floating nymphs, emergers, or duns, and what size Sulphur they are taking. The invaria duns can be hook size 14 or 16. The possibility of confusing them with the smaller Ephemerella dorothea adds to the Sulphur challenge. Remember that the solution to this puzzle may vary from fish to fish, and you should switch flies or switch fish quickly if what you're trying isn't working.

Pictures of 46 Mayfly Specimens in the Species Ephemerella invaria:

Specimen Page:1234...6
Male Ephemerella invaria (Sulphur Dun) Mayfly DunMale Ephemerella invaria (Sulphur Dun) Mayfly Dun View 6 Pictures
Collected May 25, 2007 from the Little Juniata River in Pennsylvania
Added to Troutnut.com by Troutnut on June 4, 2007
Ephemerella invaria (Sulphur Dun) Mayfly NymphEphemerella invaria (Sulphur Dun) Mayfly Nymph View 8 PicturesThis small Ephemerella invaria nymph was at least a month away from emergence.
Collected April 19, 2006 from the Beaverkill River in New York
Added to Troutnut.com by Troutnut on April 21, 2006
Male Ephemerella invaria (Sulphur Dun) Mayfly SpinnerMale Ephemerella invaria (Sulphur Dun) Mayfly Spinner View 12 Pictures
Collected June 3, 2005 from the Teal River in Wisconsin
Added to Troutnut.com by Troutnut on May 24, 2006
Specimen Page:1234...6

2 Streamside Pictures of Ephemerella invaria Mayflies:

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This Ephemerella invaria sulphur dun got stuck in its shuck trying to emerge. This isn't exactly a "natural" pose for a photograph, but it kind of shows what an emerger pattern could look like. In this picture: Mayfly Species Ephemerella invaria (Sulphur Dun). From the Neversink River in New York.
This Ephemerella invaria sulphur dun got stuck in its shuck (
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Here's an underwater view of the pupal shucks of several already-emerged Brachycentrus numerosus caddisflies.
Here's an underwater view of the pupal shucks of several already-emerged Brachycentrus numerosus caddisflies.
Shuck: The shed exoskeleton left over when an insect molts into its next stage or instar. Most often it describes the last nymphal or pupal skin exited during emergence into a winged adult.) trying to emerge. This isn't exactly a "natural" pose for a photograph, but it kind of shows what an emerger pattern could look like.

In this picture: Mayfly Species Ephemerella invaria (Sulphur Dun).
StateNew York
LocationNeversink River
Date TakenMay 20, 2007
Date AddedJun 5, 2007
AuthorTroutnut
CameraPENTAX Optio WPi
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The underside of a freshly emerged Ephemerella invaria dun. In this picture: Mayfly Species Ephemerella invaria (Sulphur Dun). From the Neversink River in New York.
The underside of a freshly emerged Ephemerella invaria dun.

In this picture: Mayfly Species Ephemerella invaria (Sulphur Dun).
StateNew York
LocationNeversink River
Date TakenMay 20, 2007
Date AddedJun 5, 2007
AuthorTroutnut
CameraPENTAX Optio WPi

15 Underwater Pictures of Ephemerella invaria Mayflies:

Underwater Photo Page:123
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Some large Ephemerella mayfly nymphs cling to a log. In the background, hundreds of Simuliidae black fly larvae swing in large clusters in the current. In this picture: Mayfly Species Ephemerella subvaria (Hendrickson), Mayfly Species Ephemerella invaria (Sulphur Dun), and True Fly Family Simuliidae (Black Flies). From the Namekagon River in Wisconsin.
Some large Ephemerella mayfly nymphs cling to a log. In the background, hundreds of Simuliidae black fly larvae swing in large clusters in the current.

In this picture: Mayfly Species Ephemerella subvaria (Hendrickson), Mayfly Species Ephemerella invaria (Sulphur Dun), and True Fly Family Simuliidae (Black Flies).
StateWisconsin
LocationNamekagon River
Date TakenMar 20, 2004
Date AddedJan 25, 2006
AuthorTroutnut
CameraOlympus C740UZ
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There's a large Ephemerella subvaria nymph in the top left. In this picture: Insect Order Trichoptera (Caddisflies), Mayfly Species Ephemerella invaria (Sulphur Dun), and Mayfly Species Ephemerella subvaria (Hendrickson). From the Namekagon River in Wisconsin.
There's a large Ephemerella subvaria nymph in the top left.

In this picture: Insect Order Trichoptera (Caddisflies), Mayfly Species Ephemerella invaria (Sulphur Dun), and Mayfly Species Ephemerella subvaria (Hendrickson).
StateWisconsin
LocationNamekagon River
Date TakenMar 20, 2004
Date AddedJan 25, 2006
AuthorTroutnut
CameraOlympus C740UZ
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The white blotches on this rock are Leucotrichia caddisfly cases, and the wispy tubes are cases made by a type of midge. In this picture: Caddisfly Species Leucotrichia pictipes (Ring Horn Microcaddis), Mayfly Species Ephemerella invaria (Sulphur Dun), and True Fly Family Chironomidae (Midges). From the Namekagon River in Wisconsin.
The white blotches on this rock are Leucotrichia caddisfly cases, and the wispy tubes are cases made by a type of midge.

In this picture: Caddisfly Species Leucotrichia pictipes (Ring Horn Microcaddis), Mayfly Species Ephemerella invaria (Sulphur Dun), and True Fly Family Chironomidae (Midges).
StateWisconsin
LocationNamekagon River
Date TakenMar 24, 2004
Date AddedJan 25, 2006
AuthorTroutnut
CameraOlympus C740UZ
Underwater Photo Page:123

Recent Discussions of Ephemerella invaria

Aw Shucks 10 Replies »
Posted by Martinlf on May 19, 2009
Last reply on Jul 24, 2009 by Martinlf
OK, this is going to seem like a major duh experience for some of you, but the other night I found a sulphur spinner on the door of a bathhouse in a campground I was staying at. Looking for other bugs I then saw a pale nymph shuck on the door. I was totally confused. A nymph this far from the stream? Was this some alien bug? Looking closer I noticed that the shape was too slender for a nymph and that the wing pads were more like little protruding pockets--and it hit me. Spinner shuck. I knew that mayflies molted to produce a spinner, but I had thought the shuck would be more insubstantial--something that would be flimsy and lack form. This was so cool, and at the same time I felt so silly for thinking it could somehow have been a nymph shuck. It's the first spinner shuck I've seen, but I assume that I'll start seeing them everywhere now, like a new word you learn. Anybody else have a spinner shuck story?
ReplyHatching Sulphur
Posted by Martinlf on Oct 14, 2008
Click on "40 more specimens" and scroll down for one photo.
Reply
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