With a seine or dip net, you can gather Baetis nymphs or adults and use the following descriptions of the mayfly's stages to identify them onstream.

Baetis nymphs swim to the surface during an emergence.

Nymphs. Baetis nymphs live in fast-moving water and are found in and around aquatic vegetation. Spring emergences begin when water temperatures pass through the mid- to high 40s F. and approach the low 50s.

The nymphs are streamlined insects that swim like minnows. They have three tails with a shorter center tail (some species have no center tail) and antennae two times longer than the width of their heads. Nymphs have single gill plates on their abdominal segments, and their bodies are tan, olive, or dark olive-brown. Size: #16-22.

Male Baetis have large, cylindrical eyes.

Duns. Male duns are best identified by their large, cylindrical, upturned eyes. Both the male and female have tiny, elliptical hind wings (some groups have none), two tails, and pale to dark-gray wings. Their bodies are light to dark olive, olive-brown, or olive-gray. Size: #16-22.

Spinners. Spinners also have large, cylindrical, upturned eyes. They have small or no elliptical hind wings, two tails, and clear wings. Their bodies are pale olive-tan to dark brown. Size: #16-22.

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