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.

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Skwala (Large Springfly) Stonefly Nymph Skwala (Large Springfly) Stonefly Nymph

Dorsal view of a Skwala (Perlodidae) (Large Springfly) Stonefly Nymph from the Yakima River in Washington

This Skwala nymph still has a couple months left to go before hatching, but it's still a good representative of its species, which was extremely abundant in my sample for a stonefly of this size. It's obvious why the Yakima is known for its Skwala hatch.

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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.

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Baetis tricaudatus (Blue-Winged Olive) Mayfly Nymph Pictures

Baetis tricaudatus (Baetidae) (Blue-Winged Olive) Mayfly Nymph from the South Fork Snoqualmie River in Washington

Ruler view of a Baetis tricaudatus (Baetidae) (Blue-Winged Olive) Mayfly Nymph from the South Fork Snoqualmie River in Washington The smallest ruler marks are 1 mm.

Ventral view of a Baetis tricaudatus (Baetidae) (Blue-Winged Olive) Mayfly Nymph from the South Fork Snoqualmie River in Washington

Dorsal view of a Baetis tricaudatus (Baetidae) (Blue-Winged Olive) Mayfly Nymph from the South Fork Snoqualmie River in Washington

There serrations of the gills that are supposed to characterize this species are maaaaybe visible on the sharpest edge of the gill in the middle, but I might just be imagining things. Crystal-clear images of the serrations are shown in a scientific paper using an electron microscope at about 2200x magnification, so I don't know if they're even visible under a dissecting microscope at all.

Baetis tricaudatus (Baetidae) (Blue-Winged Olive) Mayfly Nymph from the South Fork Snoqualmie River in Washington

Mouth parts, ventral view, with the labium removed

Baetis tricaudatus (Baetidae) (Blue-Winged Olive) Mayfly Nymph from the South Fork Snoqualmie River in Washington

View of the labium removed from the rest of the head, since the shape of the labial palp is an important identifying characteristic

Baetis tricaudatus (Baetidae) (Blue-Winged Olive) Mayfly Nymph from the South Fork Snoqualmie River in Washington

I took this picture to capture the markings on the pronotum, after I had removed the head to dissect mouthparts.

Baetis tricaudatus (Baetidae) (Blue-Winged Olive) Mayfly Nymph from the South Fork Snoqualmie River in Washington

There were some short, stout setae on the pedicels, a key characteristic, but I couldn't get a sharp enough photo for you to see them.

Baetis tricaudatus (Baetidae) (Blue-Winged Olive) Mayfly Nymph from the South Fork Snoqualmie River in Washington

This mayfly was collected from the South Fork Snoqualmie River in Washington on May 14th, 2022 and added to Troutnut.com by Troutnut on May 16th, 2022.

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