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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.

Dorsal view of a Skwala (Perlodidae) (Large Springfly) Stonefly Nymph from the Yakima River in Washington
This Skwala nymph still has a couple months left to go before hatching, but it's still a good representative of its species, which was extremely abundant in my sample for a stonefly of this size. It's obvious why the Yakima is known for its Skwala hatch.
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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Caddisfly Genus Frenesia (Dot Wing Winter Sedges)

Where & when

Time of year : Late September through February, peaking in November or December

In 73 records from GBIF, adults of this genus have mostly been collected during October (30%), November (21%), September (14%), August (10%), July (8%), June (7%), and May (5%).

In 4 records from GBIF, this genus has been collected at elevations of 164, 299, 1100, and 3609 ft.

Genus Range

Hatching behavior

Time of day : Late morning or afternoon

Pupae emerge from the shallows on warm days, and are the most important stage of this species. They can be very important because few other insects are around at the same time of year.

Egg-Laying behavior

The egg-laying females are not known to be important.

Larva & pupa biology

Diet: Decaying plant matter

Environmental tolerance: Prefers cold water

Start a Discussion of Frenesia


Caddisfly Genus Frenesia (Dot Wing Winter Sedges)

Species in Frenesia: Frenesia difficilis, Frenesia missa
Genus Range
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