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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 Pycnopsyche guttifera (Limnephilidae) (Great Autumn Brown Sedge) Caddisfly Larva from the Yakima River in Washington
This specimen appears to be of the same species as this one collected in the same spot two months earlier. The identification of both is tentative. This one suffered some physical damage before being photographed, too, so the colors aren't totally natural. I was mostly photographing it to test out some new camera setting idea, which worked really well for a couple of closeups.
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 Species Callibaetis montanus (Speckled Duns)

Where & when

In 1 records from GBIF, adults of this species have been collected during July (100%).

Species Range

Physical description

Most physical descriptions on Troutnut are direct or slightly edited quotes from the original scientific sources describing or updating the species, although there may be errors in copying them to this website. Such descriptions aren't always definitive, because species often turn out to be more variable than the original describers observed. In some cases, only a single specimen was described! However, they are useful starting points.

Female Spinner

Body length: 6 mm
Wing length: 8 mm

A brownish yellow species; cross veins of fore wing few in number; marginal intercalaries occur singly; male not known.

“Body discolored; notum testaceous, irrorated on each side with brown ochre, and traversed lengthwise by a median brown-ochreous stripe intersected by a light yellowish line” (Eaton). Legs “somewhat of a dull light Vandyke brownish-grey, stippled or irrorated minutely and densely in the femora with very light burnt umber brown”; tarsal joinings similar in color; distal joints of the tarsi darkened, claws black. Wings vitreous; cross veins of fore wing few in number, intercalaries single. Costal vitta light raw-umber brown in color, occupying the costal, subcostal and “next adjoining spaces,” and widened at the base of the wing; this band varies in intensity apically and in the basal costal space. Veins similar in color, except the basal costal cross veins, which are whitish. 6 or 7 cross veins before the bulla; beyond it “about 7 rudimentary and 7 well-defined simple and almost straight” cross veins. Tails white; joinings and basal joints yellowish.

Start a Discussion of Callibaetis montanus


  • Needham, James G., Jay R. Traver, and Yin-Chi Hsu. 1935. The Biology of Mayflies. Comstock Publishing Company, Inc.

Mayfly Species Callibaetis montanus (Speckled Duns)

Species Range
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