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Lateral view of a Male Baetis (Baetidae) (Blue-Winged Olive) Mayfly Dun from Mystery Creek #43 in New York
Blue-winged Olives

Tiny Baetis mayflies are perhaps the most commonly encountered and imitated by anglers on all American trout streams due to their great abundance, widespread distribution, and trout-friendly emergence habits.

Lateral view of a Psychodidae True Fly Larva from Mystery Creek #308 in Washington
This wild-looking little thing completely puzzled me. At first I was thinking beetle or month larva, until I got a look at the pictures on the computer screen. I made a couple of incorrect guesses before entomologist Greg Courtney pointed me in the right direction with Psychodidae. He suggested a possible genus of Thornburghiella, but could not rule out some other members of the tribe Pericomini.
27" brown trout, my largest ever. It was the sub-dominant fish in its pool. After this, I hooked the bigger one, but I couldn't land it.
Troutnut is a project started in 2003 by salmonid ecologist Jason "Troutnut" Neuswanger to help anglers and fly tyers unabashedly embrace the entomological side of the sport. Learn more about Troutnut or support the project for an enhanced experience here.

Mayfly Species Heptagenia culacantha

This species is not known to be important to anglers. It is noteworthy for its relatively recent discovery, its large size, and the striking coloration of its nymphs and duns. They are sometimes called Tiger Mayflies.

This is the largest species of Heptagenia on the continent, and it's also one of the largest in the entire Heptageniidae family. Nymphs and adult females have been collected with bodies up to a size of 19.5mm, a little over 3/4" long.

Where & when

Time of year : May to early June

Preferred waters: Large rivers

In the paper announcing its discovery, this mayfly was reported only from two very large rivers in New York and Pennsylvania, the Delaware and the Susquehanna. The authors first discovered the nymphs and duns in the Susquehanna near Three Mile Island, PA in 1980, and in 1982 they found more nymphs which they raised into eight spinners. They later figured out that several specimens collected from the Delaware and Susquehanna in 1974 belonged to this new species.

This mayfly is very hard to find, even for experts who know where to look. The discovering scientists wrote, "rarely was more than one nymph found on the underside of the same rock." Their attempt to find more specimens in 1981 was unsuccessful. However, the species seems to still be around. The Mayflies of the United States geographic database shows additional records from far northeastern New York and south-central Pennsylvania.

Delaware River fishing guide Paul Weamer of Border Water Outfitters found and photographed a female Heptagenia culacantha dun in 2005, and his photos are posted and discussed in a "name that mayfly" contest on the Fly Fisherman magazine forum. Heptagenia flavescens was incorrectly suggested, but it wasn't far off the mark: Evans (1985) mentions that it is Heptagenia culacantha's closest relative.
Species Range

Nymph biology

Substrate: Underside of large rubble and boulders

Environmental tolerance: Known mainly from a fairly warm trout river and a warmwater river

The nymphs are supposed to be strikingly colored yellow with brown markings. The scientific description brings to mind a color pattern similar to the Perlidae (golden stoneflies).

Specimens of the Mayfly Species Heptagenia culacantha

1 Male Dun
1 Male Spinner

Discussions of Heptagenia culacantha

Added more Heptagenia culacantha info
12 replies
Posted by Troutnut on Dec 19, 2006
Last reply on Feb 8, 2012 by Entoman
I went to the entomology library today and photocopied the 1985 paper that first described this curious species. I've updated the culacantha page with this information.
Link to pictures of H. culacantha
2 replies
Posted by Troutnut on Oct 20, 2006
Last reply on Oct 4, 2007 by Troutnut
Many thanks to user Softhackle for digging up this link. I knew about the thread from back when it started, but I wasn't able to find it when I went back to look last night. Good work!

Fly Fisherman Magazine forum topic with two pictures of a H. culacantha dun.

I've added the species to the "live" part of the database and put up a rudimentary page where I can compile any more information we find.
Does anyone know anything about Heptagenia culacantha?
8 replies
Posted by GONZO on Oct 19, 2006
Last reply on Apr 18, 2007 by Konchu
This is a shot in the dark, but I'm trying to track down descriptive information about a rather rare "mystery mayfly." Heptagenia culacantha was identified in 1985 (Evans, Botts, & Flowers). About all I have right now is a tease from the Journal of the New York Entomological Society--"This infrequently taken species, one of the largest and most striking North American heptageniids, is known only from Pennsylvania and New York."

The reason I'm so interested is that I believe I encounter a fishable hatch of these mayflies every season on one of my favorite PA brook trout headwaters. If that conjures a picture of fishing to 6-7" dinks, you'll need to double those numbers to appreciate how special this stream really is. Add to that an image of the fish rising to these beautiful "mystery mayflies" that hatch in the evening, following a day-long emergence of Dark Green Drakes (Litobrancha recurvata)!

It is such a special event that it is one of the very few things that can pull me away from fishing my favorite Olive Morning Dun hatch (Drunella lata, nee cornuta). Help!

Start a Discussion of Heptagenia culacantha


  • Evans, J.L., Botts, W.F. Jr. and R.W. Flowers. 1985. A new Heptagenia (Ephemeroptera: Heptageniidae) from the Susquehanna and Delaware Rivers from eastern North America. Annals of the Entomological Society of America 78: 5-7.

Mayfly Species Heptagenia culacantha

Species Range
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