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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
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.

Dorsal view of a Setvena wahkeena (Perlodidae) (Wahkeena Springfly) Stonefly Nymph from Mystery Creek #199 in Washington
As far as I can tell, this species has only previously been reported from one site in Oregon along the Columbia gorge. However, the key characteristics are fairly unmistakable in all except for one minor detail:
— 4 small yellow spots on frons visible in photos
— Narrow occipital spinule row curves forward (but doesn’t quite meet on stem of ecdysial suture, as it's supposed to in this species)
— Short spinules on anterior margin of front legs
— Short rposterior row of blunt spinules on abdominal tergae, rather than elongated spinules dorsally
I caught several of these mature nymphs in the fishless, tiny headwaters of a creek high in the Wenatchee Mountains.
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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Great Speckled Spinners

This common name refers to only one species. Click its scientific name to learn more.

Mayfly Species Siphloplecton basale

These are often called Great Speckled Spinners.
Sadly, the largest mayflies of the early season come in small quantities. Siphloplecton basale matches the impressive size of the Ephemera drakes which follow two months later, but it does not match their numbers. It is common on one of my favorite rivers to see ten to fifteen of these elegant drakes dancing over a riffle in the early Spring. They are difficult to miss in the air, but on the water that quantity cannot get the trout or the angler excited.

There are rumors of fishable Siphloplecton days, but I know none of the details. They might be locally important in places angler-entomologists have yet to visit in the prime months, an unsung local treasure like Baetisca laurentina.
Lateral view of a Male Siphloplecton basale (Metretopodidae) (Pseudo-Gray Drake) Mayfly Dun from the Namekagon River in Wisconsin
This one hatched on the same April Saturday that I saw the first Hendricksons of the season.
Lateral view of a Male Siphloplecton basale (Metretopodidae) (Pseudo-Gray Drake) Mayfly Spinner from the Namekagon River in Wisconsin
I went to great comical lengths to swipe this spinner from the air with a little aquarium net I carry with me while I'm fishing. Siphloplecton basale spinners fly fast and high over the riffles, and there are never very many of them, so they're difficult to catch.
Siphloplecton basale (Metretopodidae) (Pseudo-Gray Drake) Mayfly Nymph from unknown in Wisconsin
This nymph has double front tarsal claws and double gills on the first three abdominal segments.

Great Speckled Spinners

Scientific Name
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