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Lateral view of a Female Hexagenia limbata (Ephemeridae) (Hex) Mayfly Dun from the Namekagon River in Wisconsin
Hex Mayflies
Hexagenia limbata

The famous nocturnal Hex hatch of the Midwest (and a few other lucky locations) stirs to the surface mythically large brown trout that only touch streamers for the rest of the year.

Ventral view of a Hydropsyche (Hydropsychidae) (Spotted Sedge) Caddisfly Larva from the Yakima River in Washington
With a bit of help from the microscope, this specimen keys clearly and unsurprisingly to Hydropsyche.
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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Scuds

Scuds are not insects but small crustaceans, sometimes called freshwater shrimp, and in some streams they are a primary food source for trout. They grow quickly and can survive in a variety of habitats, but they are most prolific and important to trout in slow, weedy spring creeks. Unlike most aquatic insects, they never "hatch" into a dry form.


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

Arthropod Order Amphipoda

These are pretty much always called Scuds.
Scuds can be an extremely important trout food source. They are often the most abundant aquatic macroinvertebrate in their habitat.

They are crustaceans so they don't go through the same life-cycle complications as aquatic insects. They start out as small scuds, grow to be big scuds, and die. The most significant family to anglers is Gammaridae with the species of the Gammarus genus heading up the list. The smaller Hyalella species of the Talitridae can also be important.

Though they all share the same silhouette, they can come in a surprising variety of sizes and colors. They run from size 8 to as small as you wish to imitate. The most common colors are olive or tan, though they can be found with yellow or gray base colors as well. Shading is often illusive to describe with highlights of pink, orange, green and even blue at times. It pays for anglers to notice both size and color differences in the waters they fish.
A freshwater amphipod (scud). Tiny crustacean common to many freshwater environments

Dorsal view of a Amphipoda (Scud) Arthropod Adult from Salmon Creek in New York

Scuds

Scientific Name
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