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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 Female Sweltsa borealis (Chloroperlidae) (Boreal Sallfly) Stonefly Adult from Harris Creek in Washington
I was not fishing, but happened to be at an unrelated social event on a hill above this tiny creek (which I never even saw) when this stonefly flew by me. I assume it came from there. Some key characteristics are tricky to follow, but process of elimination ultimately led me to Sweltsa borealis. It is reassuringly similar to this specimen posted by Bob Newell years ago. It is also so strikingly similar to this nymph from the same river system that I'm comfortable identifying that nymph from this adult. I was especially pleased with the closeup photo of four mites parasitizing this one.
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.
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Al514's profile picture
Central New York

Posts: 142
Al514 on Sep 17, 2007September 17th, 2007, 2:29 pm EDT
What is the biggest mayfly species in the North East? I was at a 7 to 8 acre pond tonight that holds some nice trout, and I swear I saw some spinners about size 8 or 6! I had to do a double-take to make sure it was a mayfly! I didnt have my camera, so no pictures but Ill try and get some soon. It looked dark brown and around 2, possibly 3 inches in length.
Al514's profile picture
Central New York

Posts: 142
Al514 on Sep 17, 2007September 17th, 2007, 2:32 pm EDT
Ok, so I originally thought it was Hex, but I didn't think they were that big. After looking at the pictures on here, I'm sure it was a Hex.
Taxon's profile picture
Site Editor
Plano, TX

Posts: 1311
Taxon on Sep 17, 2007September 17th, 2007, 3:45 pm EDT
There are only three mayfly genera with really large mayflies, which I would describe as being in excess of 1" in length, as measured from the front of head to end of abdomen, exclusive of tails.

These are Ephemera, Hexagenia, and Litobrancha, all burrowers in family Ephemeridae. Of those three genera, only Hexagenia are found in ponds.
Best regards,
Roger Rohrbeck
Troutnut's profile picture
Bellevue, WA

Posts: 2758
Troutnut on Sep 17, 2007September 17th, 2007, 7:17 pm EDT
At this time of year, it was probably a different species of Hex, like Hexagenia atrocaudata. Check out the pics of that one on this site and see if they match a little closer still.
Jason Neuswanger, Ph.D.
Troutnut and salmonid ecologist

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