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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 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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Mayfly Genus Anthopotamus (Golden Drakes)

These mayflies have something for everyone. For the angler, they offer a chance to fish large dry flies to a rise on midsummer evenings when little else is on the water. To the entomologist they are interesting for their unique placement mid-way between the burrower and crawler groups of nymphs. Another curious characteristic is that the eyes of the adults are the same size in both genders; this is very unusual in mayflies.

Where & when

Time of year : Late June through August

Preferred waters: Mostly medium to large rivers

See the individual species pages for distribution and timing details. Anthopotamus distinctus is the main species in the East, and Anthopotamus myops is more common in the Midwest.

In 99 records from GBIF, adults of this genus have mostly been collected during June (48%), July (34%), and August (12%).

In 34 records from GBIF, this genus has been collected at elevations ranging from 618 to 5003 ft, with an average (median) of 3133 ft.

Genus Range

Hatching behavior

Time of day : Throughout late evening, peaking at dusk, sometimes after dark on hot days.

Habitat: Slow to medium water

Water temperature: 65-70°F

These mayflies emerge fairly quickly, but they may linger on the surface for a while as their wings dry, making dun patterns the imitation of choice. They can make some commotion which is worth imitating if a still pattern does not work.

Caucci and Nastasi in Hatches II say that the duns begin hatching when the temperature drops below 70°F in the evenings. However, in Matching the Hatch, Ernest Schwiebert reports a hatch when the water temperature was a steamy 78°F. The trout are unlikely to respond at such times.

Spinner behavior

Time of day: Twilight to late night

Ted Fauceglia writes in Mayflies that the best trout activity associated with these spinner falls happens well after dark. This is the only mention of fishing to the spinners that I've found.

Nymph biology

Current speed: Slow to Medium

Substrate: Detritus over sand, gravel, or silt

Environmental tolerance: They have an unusually high tolerance for warm, shallow water.

The nymphs of this genus are the unique representatives of a transitional step between the crawler nymph group and the burrower nymphs. They don't dig U-shaped burrows into the sediment like Ephemeridae nymphs do, but they do settle down into indentations in the detritus.

They become active on the bottom shortly before emerging, and fishing nymph imitations before the hatch may reward the angler.

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Mayfly Genus Anthopotamus (Golden Drakes)

Genus Range
Common Name
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