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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.

Dorsal view of a Grammotaulius betteni (Limnephilidae) (Northern Caddisfly) Caddisfly Larva from the Yakima River in Washington
This is a striking caddis larva with an interesting color pattern on the head. Here are some characteristics I was able to see under the microscope, but could not easily expose for a picture:
- The prosternal horn is present.
- The mandible is clearly toothed, not formed into a uniform scraper blade.
- The seems to be only 2 major setae on the ventral edge of the hind femur.
- Chloride epithelia seem to be absent from the dorsal side of any abdominal segments.
Based on these characteristics and the ones more easily visible from the pictures, this seems to be Grammotaulius. The key's description of the case is spot-on: "Case cylindrical, made of longitudinally arranged sedge or similar leaves," as is the description of the markings on the head, "Dorsum of head light brownish yellow with numerous discrete, small, dark spots." The spot pattern on the head is a very good match to figure 19.312 of Merritt R.W., Cummins, K.W., and Berg, M.B. (2019). The species ID is based on Grammotaulius betteni being the only species of this genus known in Washington state.
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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