Lateral view of a Male Baetis (Baetidae) (Blue-Winged Olive) Mayfly Dun from Mystery Creek #43 in New York

Blue-winged Olives
Baetis

Tiny Baetis mayflies are perhaps the most commonly encountered and imitated by anglers on all American trout streams due to their great abundance, widespread distribution, and trout-friendly emergence habits.

We were lucky to be able to fish through this storm as it skirted around us to the north, giving us just enough clouds to prompt a BWO hatch but keeping the lighting at a safe distance.

From Slough Creek in Wyoming

Stream photos

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Ephemerella mucronata Mayfly Nymph Ephemerella mucronata Mayfly Nymph

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.

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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.

Troutnut is a project started in 2003 by salmonid ecologist Jason "Troutnut" Neuswanger to help anglers and fly tyers unabashedly embrace the entomological side of the sport. Learn more about Troutnut or support the project for an enhanced experience here.

Specific collection sites for Micrasema

The specific collection location data from this map were pulled from the Global Biodiversity Information Facility (GBIF) website under the Creative Commons license. Data there come from a variety of sources, some of which are populated by hobbyists. Both the precision of the location and accuracy of the identification could be low. This map is not an authoritative scientific source, nor an exhaustive list of everwhere this taxon is found, but it should be good enough for anglers. Click each marker on the map for more information about that report, including a link to more details on GBIF.

There are 3029 reported locations for this taxon in the database. Only randomly selected 2000 have been shown here to avoid overloading your browser. Reloading the page will again choose a random 2000.

Blue-winged OlivesBaetis

Specific collection sites for Micrasema

Specific collection sites for Micrasema

Blue-winged Olives
Baetis