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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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Stonefly Genus Isoperla (Stripetails and Yellow Stones)

This is a very common trout stream stonefly genus. It is also huge, with sixty species scattered over the entire continent. Though anglers usually call them Little Yellow Stones or Yellow Sallies, the scientific common name for this genus is Stripetail. The latter is probably better to use as not all of them are necessarily little or yellow.

Where & when

In 510 records from GBIF, adults of this genus have mostly been collected during May (33%), June (30%), April (17%), and July (14%).

In 335 records from GBIF, this genus has been collected at elevations ranging from 26 to 11430 ft, with an average (median) of 1909 ft.

Genus Range

Specimens of the Stonefly Genus Isoperla

5 Adults
3 Male Adults
1 Female Adult
8 Nymphs

Start a Discussion of Isoperla

References

Stonefly Genus Isoperla (Stripetails and Yellow Stones)

Taxonomy
34 species (Isoperla bellona, Isoperla conspicua, Isoperla cotta, Isoperla coushatta, Isoperla davisi, Isoperla decepta, Isoperla decolorata, Isoperla distincta, Isoperla emarginata, Isoperla extensa, Isoperla francesca, Isoperla frisoni, Isoperla grammatica, Isoperla gravitans, Isoperla irregularis, Isoperla jewetti, Isoperla katmaiensis, Isoperla lata, Isoperla longiseta, Isoperla major, Isoperla maxana, Isoperla mohri, Isoperla namata, Isoperla nana, Isoperla orata, Isoperla ouachita, Isoperla petersoni, Isoperla phalerata, Isoperla punctata, Isoperla richardsoni, Isoperla sagittata, Isoperla slossonae, Isoperla szczytkoi, and Isoperla transmarina) aren't included.
Genus Range
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