Mayfly Species Penelomax septentrionalis

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Taxonomic Navigation -?-

Kingdom Animalia (Animals)

» Phylum Arthropoda (Arthropods)

» Class Insecta (Insects)

» Order Ephemeroptera (Mayflies)

» Family Ephemerellidae (Hendricksons, Sulphurs, PMDs, BWOs)

» Genus Penelomax

» Species septentrionalis

Pictures Below ↓

This fascinating mayfly is among the most distinctive in the Ephemerellidae family, because it has unusually long legs in both the nymphal and adult stages. The nymphs have a strikingly rugged, spindly appearance, and the adults are a strikingly deeper, amber-yellow color than other Ephemerellidae duns.

This species was overlooked in the fly-fishing literature for many years. The first details appear in Fly-Fishing Pressured Water, which states that this species (formerly called Ephemerella septentrionalis) sometimes supports hatches of Ephemerella invaria. Ernest Schwiebert's Nymphs Volume I: The Mayflies: The Major Species seconds that claim, suggesting that it generates fishable hatches which may go unnoticed due to confusion with both Ephemerella invaria and Ephemerella dorothea. However, the long legs, thin dorsal (Dorsal: Top.) stripe, and more vivid color make it easy to tell them apart upon close inspection.

Where & When

Region: East

Time Of Year (?): May through midsummer

There are records of this species from Tennessee north into Ontario and Quebec. They begin in early May near the southern end of their range, and continue into midsummer in Canada. Expect them from mid-May through early June in the popular fly fishing waters of Pennsylvania and New York, from the limestone spring creeks to the freestone Catskill and Poconos waters. Their timing coincides with the more common and similar Ephemerella invaria.

Hatching Behavior

Time Of Day (?): Late afternoon early in the season; twilight later on

Spinner Behavior

Time Of Day: Twilight

Nymph Biology

Substrate: Weedy stretches of stream

These nymphs may be most abundant in very small streams, but they are known from larger rivers as well, and I have collected them from the main stem of the Delaware.

Pictures of 3 Mayfly Specimens in the Species Penelomax septentrionalis:

Penelomax septentrionalis Mayfly Nymph

View 12 PicturesThis is surely the most distinctive-looking species in Ephemerellidae. I like the rugged, spindly look. If mayflies made movies, Penelomax septentrionalis would probably play the supervillain.

Maybe I should take a break and get something to eat.

Collected May 13, 2007 from the Delaware River in New York
Added to Troutnut.com by Troutnut on May 18, 2007

Female Penelomax septentrionalis Mayfly Dun

View 10 PicturesI'm confident this dun belongs to septentrionalis, because her legs are just too long for any other Ephemerellid, and her unusual mid-dorsal (Dorsal: Top.) stripe matches those of two easily identified nymphs I collected some miles downstream.

This really pretty mayfly was in kind of bad shape when I found it crippled on the surface, and bouncing around in my container with a bunch of green drakes didn't help.

Collected June 1, 2007 from the West Branch of the Delaware River in New York
Added to Troutnut.com by Troutnut on June 4, 2007

Penelomax septentrionalis Mayfly Nymph

View 3 Pictures

Collected May 13, 2007 from the Delaware River in New York
Added to Troutnut.com by Troutnut on May 18, 2007

Recent Discussions of Penelomax septentrionalis

Anyone know more about Ephemerella septentrionalis? 11 Replies »

Posted by Troutnut on May 18, 2007

Last reply on Jul 18, 2011 by Oldredbarn

I found about one sentence on these in Gonzo's book, and haven't seen them mentioned anywhere else in fly fishing literature. Nor is any of the scientific literature I have on them particularly interesting (just descriptions). Now that I've collected a few and see what unique-looking nymphs they've got, I'm really curious about them.

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Jargon Defined:

Dorsal: Top.

Duns: 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.

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:

Gonzales, Lloyd. 2005. Fly-Fishing Pressured Water. Stackpole Books.

Schwiebert, Ernest G. 2007. Nymphs Volume I: The Mayflies: The Major Species. The Lyons Press.