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Macroinvertebrate Identification Key

Amphipoda (scuds)

Click image to view a photo gallery of aquatic macroinvertebrates.

Macroinvertebrates are animals without a backbone that can be seen with the naked eye. These bottom-dwelling animals include crustaceans and worms but most are aquatic insects. Beetles, caddisflies, stoneflies, mayflies, hellgrammites, dragonflies, true flies, and some moths are among the groups of insects represented in streams. Macroinvertebrates are an important link in the food web between the producers (leaves, algae) and higher consumers such as fish.

Visit the Stroud Center’s Leaf Pack Network® website to learn about a simple experiment that uses tree leaves and aquatic insects to determine the health of your local stream.

Using the Macroinvertebrate Key

If you want to identify an aquatic macroinvertebrate you found in a stream, scroll down to use our identification key. Our key is an example of a dichotomous key — at each step you choose between two mutually exclusive statements about a characteristic. The key starts with the choice between “jointed legs” and “no jointed legs.” After you make that choice you move to the next pair of choices in the key. Follow the page reference (e.g. “Go to Slide 3”) to jump to the next part of key. Continue until you arrive at an identification.

Terms of Use

Users are free to print and duplicate this key for education purposes always maintaining the Stroud Center’s copyrighted logo. Edits or resale of the key are not permitted without a written agreement with Stroud Water Research Center. Email educationprograms@stroudcenter.org for more information.

We have changed the way we offer downloads of the macroinvertebrate identification key. You may have reached this page because you were looking for the old images. If so, please read the Terms of Use above and then click on the image to download the complete key.

Cover image of the Identification Guide to Freshwater Macroinvertebrates

Click on the image to download the key.