Mayfly Species Ephemerella invaria (Sulphur)
Taxonomic Navigation -?-
Kingdom Animalia (Animals)
» Phylum Arthropoda (Arthropods)
» Class Insecta (Insects)
» Order Ephemeroptera (Mayflies)
» Family Ephemerellidae (Hendricksons, Sulphurs, PMDs, BWOs)
» Genus Ephemerella (Hendricksons, Sulphurs, PMDs)
» Species invaria (Sulphur)
Common Names
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
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.Habitat: Almost anywhere, but best near fast runs and riffles.
Water Temperature: 52-60°F
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. Habitat: Riffles
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.Substrate: Many types, but gravel is preferred
Environmental Tolerance: Unlike Ephemerella subvaria, invaria is very tolerant of a wide range of conditions.
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.43 Mayfly Specimens in the Species Ephemerella invaria:
Ephemerella invaria (Sulphur) Mayfly Spinner
View 12 Pictures
View 12 PicturesRegion: Upper Midwest
Collected Jun 3, 2005
Added May 25, 2006
Ephemerella invaria (Sulphur) Mayfly Spinner
View 12 Pictures
View 12 PicturesRegion: Upper Midwest
Collected Jun 3, 2005
Added May 25, 2006
Ephemerella invaria (Sulphur) Mayfly Nymph
View 8 PicturesThis small Ephemerella invaria nymph was at least a month away from emergence.
View 8 PicturesThis small Ephemerella invaria nymph was at least a month away from emergence.Region: Catskills
Collected Apr 19, 2006
Added Apr 21, 2006
2 Streamside Pictures of Ephemerella invaria Mayflies:
View Full Size
This Ephemerella invaria sulphur dun got stuck in its shuck (
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).
View Full SizeHere's an underwater view of the pupal shucks of several already-emerged Brachycentrus numerosus caddisflies.
In this picture: Mayfly Species Ephemerella invaria (Sulphur).
The underside of a freshly emerged Ephemerella invaria dun.
In this picture: Mayfly Species Ephemerella invaria (Sulphur).
In this picture: Mayfly Species Ephemerella invaria (Sulphur).
15 Underwater Pictures of Ephemerella invaria Mayflies:
There's a large Ephemerella subvaria nymph in the top left.
In this picture: Insect Order Trichoptera (Caddisflies), Mayfly Species Ephemerella invaria (Sulphur), and Mayfly Species Ephemerella subvaria (Hendrickson).
In this picture: Insect Order Trichoptera (Caddisflies), Mayfly Species Ephemerella invaria (Sulphur), and Mayfly Species Ephemerella subvaria (Hendrickson).
The mayfly and stonefly nymphs in this picture blend in extremely well.
In this picture: Mayfly Species Ephemerella invaria (Sulphur) and Insect Order Plecoptera (Stoneflies).
In this picture: Mayfly Species Ephemerella invaria (Sulphur) and Insect Order Plecoptera (Stoneflies).
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