Macroinvertebrate Identification Key

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.

Acari (water mites)

Can you tell the difference between a damselfly and a mayfly?

We can help. If you want to identify an aquatic macroinvertebrate you found in a stream, scroll down to use our macroinvertebrate identification key.

You can also view a photo gallery of more than 50 aquatic invertebrates.

Using the online key

The macroinvertebrate identification key is an example of a dichotomous key. At each step you choose between two mutually exclusive statements about a characteristic.

This 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 Page 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 Stroud Water Research Center’s copyrighted logo. Edits or resale of the key are not permissible without written agreements with the Stroud Center. Download the macroinvertebrate key

First, familiarize yourself with the characteristics you will be using to identify your macroinvertebrate.

Major Characteristics of Aquatic Larvae

Next, step through each characteristic, using the “go to” links to jump to the next part of the key.

Go to Page 2 Go to Page 3 Macroinvertebrate Key Page 1