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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 Allocapnia (Little Snowflies)

Allocapnia granulata is the most abundant Capniidae species in the East.

Where & when

In 615 records from GBIF, adults of this genus have mostly been collected during March (29%), February (26%), January (20%), December (11%), and April (10%).

In 82 records from GBIF, this genus has been collected at elevations ranging from 125 to 4856 ft, with an average (median) of 3182 ft.

Genus Range

Discussions of Allocapnia

Little Black Stonefly pics
12 replies
Posted by Adirman on Apr 14, 2018 in the species Allocapnia granulata
Last reply on Apr 21, 2018 by Martinlf
Hey guys, went out on the Neversink for awhile today and had a look around, saw a lot of little dark flies, may be the little black stone fly? Hard to tell cuz looked like Caddis too. Looks like about a size 16? Any pics of available of this species would be great.


Thanks

Start a Discussion of Allocapnia

References

Stonefly Genus Allocapnia (Little Snowflies)

Taxonomy
16 species (Allocapnia brooksi, Allocapnia frisoni, Allocapnia fumosa, Allocapnia illinoensis, Allocapnia jeanae, Allocapnia loshada, Allocapnia malverna, Allocapnia mohri, Allocapnia oribata, Allocapnia peltoides, Allocapnia recta, Allocapnia simmonsi, Allocapnia tennessa, Allocapnia vivipara, Allocapnia warreni, and Allocapnia wrayi) aren't included.
Genus Range
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