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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 Glossosoma (Glossosomatidae) (Little Brown Short-horned Sedge) Caddisfly Larva from the Yakima River in Washington
I caught this tiny larva without a case, but it seems to key pretty clearly to to Glossosomatidae. From there, the lack of sclerites on the mesonotum points to either Glossosoma or Anagapetus. Although it's difficult to see in a 2D image from the microscope, it's pretty clear in the live 3D view that the pronotum is only excised about 1/3 of its length to accommodate the forecoxa, not 2/3, which points to Glossosoma at Couplet 5 of the Key to Genera of Glossosomatidae Larvae.
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.

Taxonomic Keys for Aquatic Invertebrate Identification

Taxonomic Keys for Aquatic Invertebrate Identification

The taxonomic keys on this website are adapted from a variety of books and scientific papers, and they represent the combined hard work of hundreds of entomologists over many decades. I claim no credit for creating them in most cases, only arranging them in a more user-friendly format and adding some illustrations. These keys only cover North American taxa. If you're new to keys, see my Introduction to Taxonomic Keys.

High-level keys

Mayfly keys

Mayfly family keys to genus

This list includes keys to genus for all North American mayfly families.

Adult stage (male spinners)
Nymph stage

Mayfly genus keys to species

Only a small number of keys all the way to species are online yet, but that's an ongoing project.

Adult stage (male spinners)
Nymph stage

Caddisfly keys

Caddisfly family keys to genus

This list includes keys to genus for all North American caddisfly families.

Adult stage
Larval stage

Stonefly keys

Stonefly family keys to genus

This list includes keys to genus for all North American mayfly families.

Adult stage
Nymph stage

Stonefly genus keys to species

Only a small number of keys all the way to species are online yet, but that's an ongoing project.

Adult stage
Nymph stage

True fly keys (midges, etc.)

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