Lateral view of a Female Hexagenia limbata (Ephemeridae) (Hex) Mayfly Dun from the Namekagon River in Wisconsin

Hex Mayflies
Hexagenia limbata

The famous nocturnal Hex hatch of the Midwest (and a few other lucky locations) stirs to the surface mythically large brown trout that only touch streamers for the rest of the year.

Stream photos

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Female Hydropsyche (Spotted Sedge) Caddisfly Adult Female Hydropsyche (Spotted Sedge) Caddisfly Adult

Lateral view of a Female Hydropsyche (Hydropsychidae) (Spotted Sedge) Caddisfly Adult from the Columbia River in Washington

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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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Male Baetis tricaudatus (Blue-Winged Olive) Mayfly Spinner Pictures

Some notes from identifying this specimen under the microscope:

1. The hind wing has three longitudinal veins, but the third is faint, short (about half the length of the wing), and close to the wing margin.
2. Then antenna is brown fading into white at the tip, and the base is ringed with white.
3. The joints of the tarsal segments on the middle and hind leg have fine black markings.

It was also collected in association with a female spinner.

Lateral view of a Male Baetis tricaudatus (Baetidae) (Blue-Winged Olive) Mayfly Spinner from Silver Creek in Idaho

Ruler view of a Male Baetis tricaudatus (Baetidae) (Blue-Winged Olive) Mayfly Spinner from Silver Creek in Idaho The smallest ruler marks are 1 mm.

Male Baetis tricaudatus (Baetidae) (Blue-Winged Olive) Mayfly Spinner from Silver Creek in Idaho

Ventral view of a Male Baetis tricaudatus (Baetidae) (Blue-Winged Olive) Mayfly Spinner from Silver Creek in Idaho

Dorsal view of a Male Baetis tricaudatus (Baetidae) (Blue-Winged Olive) Mayfly Spinner from Silver Creek in Idaho

The antennae: brown, fading to white at the tip, with the base ringed with white.

Male Baetis tricaudatus (Baetidae) (Blue-Winged Olive) Mayfly Spinner from Silver Creek in Idaho

This view of the hind wing, seen through the forewing (which makes it a bit confusing), shows some of the 3rd longitudinal vein right along the bottom edge extending about half-way through the wing.

Male Baetis tricaudatus (Baetidae) (Blue-Winged Olive) Mayfly Spinner from Silver Creek in Idaho

Black markings around the tarsal joinings of the hind leg.

Male Baetis tricaudatus (Baetidae) (Blue-Winged Olive) Mayfly Spinner from Silver Creek in Idaho

This mayfly was collected from Silver Creek in Idaho on September 4th, 2020 and added to Troutnut.com by Troutnut on September 18th, 2020.

Discussions of this Spinner

Baetis bicaudatus

12 replies

Posted by Taxon on Nov 7, 2020

Last reply on Nov 12, 2020 by Millcreek

Hi Jason-

I believe this male imago to be Baetis bicaudatus.

Baetis adult species IDs?

Posted by Troutnut on Nov 6, 2020

Last reply on Nov 6, 2020 by Troutnut

Does anyone here know any decent resources for identifying adult Baetis? I haven't found much.

This specimen sure seems to nicely fit the original description of Baetis alius adults. But I can't find very precise descriptions (let alone a key) for flavistriga and tricaudatus, both of which are other likely options given the location.

These made for a good fishable hatch on Silver Creek, so it sure would be nice to know what they are.

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