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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 Ephemerella mucronata (Ephemerellidae) Mayfly Nymph from the Yakima River in Washington
This is an interesting one. Following the keys in Merritt R.W., Cummins, K.W., and Berg, M.B. (2019) and Jacobus et al. (2014), it keys clearly to Ephemerella. Jacobus et al provide a key to species, but some of the characteristics are tricky to interpret without illustrations. If I didn't make any mistakes, this one keys to Ephemerella mucronata, which has not previously been reported any closer to here than Montana and Alberta. The main character seems to fit well: "Abdominal terga with prominent, paired, subparallel, spiculate ridges." Several illustrations or descriptions of this holarctic species from the US and Europe seem to match, including the body length, tarsal claws and denticles, labial palp, and gill shapes. These sources include including Richard Allen's original description of this species in North America under the now-defunct name E. moffatae in Allen RK (1977) and the figures in this description of the species in Italy.
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 Hesperophylax (Silver Striped Sedges)

These are very large caddisflies, up to 1.3 inches long as adults.

Where & when

Time of year : Emergence in summer, egg-laying in fall

In 248 records from GBIF, adults of this genus have mostly been collected during July (23%), August (21%), June (18%), September (13%), May (12%), and October (6%).

In 139 records from GBIF, this genus has been collected at elevations ranging from 3 to 31496 ft, with an average (median) of 6289 ft.

Genus Range

Hatching behavior

Time of day : Nighttime

Prior to emergence the pupae gather on certain bolders, which concentrates their emergence into specific feeding lanes. They are just the sort of large insect that nocturnal trout like to eat.

Hesperophylax Fly Fishing Tips

LaFontaine notes in Caddisflies that the adults are worth imitating, and they make a good searching pattern, but he does not give specifics about their behavior.

Specimens of the Caddisfly Genus Hesperophylax

1 Female Adult
1 Larva

Start a Discussion of Hesperophylax

References

Caddisfly Genus Hesperophylax (Silver Striped Sedges)

Taxonomy
Species in Hesperophylax
Hesperophylax designatus
1
1
Species in Hesperophylax: Hesperophylax designatus
5 species (Hesperophylax alaskensis, Hesperophylax consimilis, Hesperophylax magnus, Hesperophylax minutus, and Hesperophylax occidentalis) aren't included.
Genus Range
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