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

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.

Dorsal view of a Amphizoa (Amphizoidae) Beetle Larva from Sears Creek in Washington
This is the first of it's family I've seen, collected from a tiny, fishless stream in the Cascades. The three species of this genus all live in the Northwest and are predators that primarily eat stonefly nymphs Merritt R.W., Cummins, K.W., and Berg, M.B. (2019).
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 Genus Ameletus (Brown Duns)

Where & when

Preferred waters: Streams of all sizes

Altitude: Up to 11,000 feet

There are many Ameletus species in the United states, but only two are regarded as significant: Ameletus velox in the West and Ameletus ludens in the East. Neither one constitutes a widespread superhatch, but they can be very abundant locally.

In 114 records from GBIF, adults of this genus have mostly been collected during June (32%), May (22%), July (18%), April (12%), and August (8%).

In 326 records from GBIF, this genus has been collected at elevations ranging from 13 to 11037 ft, with an average (median) of 1152 ft.

Genus Range

Hatching behavior

These mayflies emerge sporadically by crawling out of the water as nymphs.

Nymph biology

Ameletus nymphs are very fast swimmers. They are occasionally mistaken (especially in early instars) for some species in the Baetidae family, having roughly similar body shape and coloration. They are easily separated under close inspection based on gill coloration and prominent mouth parts. As mature nymphs their large size and intense maculation (the scientific common name for this family in some circles is Painted Minnow nymph) make them much easier to differentiate from others.

Specimens of the Mayfly Genus Ameletus

3 Male Duns
5 Male Spinners
2 Female Spinners
15 Nymphs

Discussions of Ameletus

Brown Dun hatch/swarm time?
10 replies
Posted by Konchu on Apr 25, 2009 in the species Ameletus ludens
Last reply on Apr 29, 2009 by Troutnut
Has anyone else watched a Brown Dun hatch or swarm? If so, what time of day did you see it, and how long did it last?

I came upon a woodland swarm late this evening. I thought I saw mating occurring higher above the stream. This would mean that parthenogenesis is not necessarily happening in "my" stream. I watched for awhile, but got distracted (venomous snake). I hope to catch it (the hatch, not the snake) again tomorrow night and note the egg-laying behavior and possibly nab some male adults for science. There's a range of nymph ages, so I should be OK, weather permitting.

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Mayfly Genus Ameletus (Brown Duns)

Genus Range
Common Name
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