Super Bowl Mayfly

March brown dun showing the distinctive mottled coloring on its wings and uniform body color.

March brown nymph (Rhithrogena). The flat shape clearly shows it’s a clinger. Also note the large overlapping gills along the side of the abdomen. They help the nymph hold on to the substrate in fast water.

Ameletus dun. Markings on the wing resemble those of the March brown. A key difference is the dark stripe-like markings seen on the abdomen of the Ameletus dun. Color of the March brown is a uniform brown.

Ameletus nymphs are slender fast swimmers, very different from the flat clinger nymph of March browns (Rhithrogena).

Super Bowl Sunday wasn’t exactly when I expected to see a mayfly at my doorstep.  But when I opened my door to let Jim Schollmeyer of “Fly Tier’s Benchside Reference” fame in for a Super Bowl gathering he handed me a film canister with a nice mayfly dun inside.

“It showed up on my patio window this morning,” he said.  “Looks like the March Browns may have started hatching already.”

When I first looked at it in the canister it certainly looked like a Western March Brown or Rhithrogena morrisoni (Family Heptageniidae). With the Super Bowl about to start, however, I decided to put off a closer look until the next day.

The next morning I set up camera gear for some photos of the year’s first March Brown.  When I began taking a really close look at this handsome mayfly through the camera’s macro lens, however, I saw some things that didn’t look quite right.  By the end of the photo shoot I new this wasn’t a March Brown, and a quick look at it through my microscope confirmed that indeed this mayfly was a Brown Dun or Ameletus sp. (Family Ameletidae).

The brown mottled wings, size (roughly a size 14 if matching with a dry fly), and early spring emergence, all make the Ameletus an easy mayfly to confuse with the March Brown. A few subtle differences however, help distinguish one from the other.  The most obvious characteristic to look for is the dark horizontal bands on the abdominal segments of the Ameletus dun.  March Brown duns have no such dark bands.  The wing venation also differs between the two, but wing venation is a confusing subject, and one I’ll have leave for another blog.

Nymphs of Ameletus and March Browns are even easier to distinguish. The torpedo shape of Ameletus nymphs clearly mark them as swimmers. Propelled by their long tails, they dart through the water like little fish. March Brown nymphs on the other hand are oval and flat, and as such are classified as mayfly clingers, which swim awkwardly at best.

In terms of fishable hatches, March Browns tend to produce the better results. For one thing Ameletus nymphs typically crawl out onto streamside rocks where the duns emerge. This reduces their availability to trout. If abundant, however, Ameletus can produce some descent fish feeding, either on the nymphs swimming towards shore to crawl out, or on duns that get blown or washed off rocks back into the water. Were trout feeding on Ameletus on Super Bowl Sunday? I’m afraid I have no idea!

The Harrop Dun shown here is a great dry fly style for imitating March Browns and Ameletus duns.