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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.

Lateral view of a Female Sweltsa borealis (Chloroperlidae) (Boreal Sallfly) Stonefly Adult from Harris Creek in Washington
I was not fishing, but happened to be at an unrelated social event on a hill above this tiny creek (which I never even saw) when this stonefly flew by me. I assume it came from there. Some key characteristics are tricky to follow, but process of elimination ultimately led me to Sweltsa borealis. It is reassuringly similar to this specimen posted by Bob Newell years ago. It is also so strikingly similar to this nymph from the same river system that I'm comfortable identifying that nymph from this adult. I was especially pleased with the closeup photo of four mites parasitizing this one.
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.

Insects

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

Arthropod Class Insecta

These are pretty much always called Insects.
Nearly a million species of insects have been described by entomologists. I have left several of them off of this site, just to save time, but I've tried to include all the main aquatic insects trout eat in North America.

This site focuses on aquatic insects, of which the most important are mayflies (Ephemeroptera) and caddisflies (Trichoptera). Stoneflies (Plecoptera) come in third, a position arguably challenged by the many two-winged true flies of the Diptera order, which includes midges and craneflies. I've also included some terrestrial insects which I've found on or near trout streams. Terrestrials like ants, beetles, and grasshoppers are an important food source for trout in many places, especially during the summer months.

Aquatic insects do not live their entire lives in the water. Instead, they grow for a year (give or take quite a bit) as nymphs or larvae underwater, and then they emerge into air-breathing winged insects for a short while to mate and die. There are many variations on this theme.

The most important aquatic insects for fly fishermen are mayflies, stoneflies, caddisflies, and midges. Mayflies and caddisflies are the most discussed by angler-entomologists, because it's so useful to closely identify them. The behavior of their species guides the behavior of feeding trout, and an angler who understands the lifecycle of a particular species has the upper hand when it's hatching. This is not so important for stoneflies and midges, because their hatching behavior is less variable.
Lateral view of a Brachycentrus appalachia (Brachycentridae) (Apple Caddis) Caddisfly Adult from the West Branch of the Delaware River in New York
I captured this specimen in the same color as this photograph, during its egg-laying flight. The emergers are much lighter.
Lateral view of a Female Stenonema (Heptageniidae) (March Browns and Cahills) Mayfly Dun from the Namekagon River in Wisconsin
Artistic view of a Male Ephemerella aurivillii (Ephemerellidae) Mayfly Spinner from Nome Creek in Alaska
This spinner molted from a dun after being photographed, and the dun form is listed here as a separate specimen. I've rarely found a more cooperative and photogenic mayfly.
Dorsal view of a Rhyacophila fuscula (Rhyacophilidae) (Green Sedge) Caddisfly Larva from Mystery Creek #62 in New York
Rhyacophila (Rhyacophilidae) (Green Sedge) Caddisfly Pupa from the Long Lake Branch of the White River in Wisconsin
I collected this pupa and several like it from the same stream and on the same day as this larva. I suspect they're the same species. Every pupa I collected was in a brown casing like the one shown in one of the pictures below. I cut this pupa out of its case after a picture so you can see more details. It is close to but not fully developed.

Insects

Scientific Name
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