How To: Hunt for Creek Critters

Biologists call the squiggly, little creepy-crawlies living in a stream “benthic macroinvertebrates.” And though they may be a mouthful to say, they’re fun to catch, and they offer clues about the health of a stream.

Say What?

“Benthic” refers to creatures that live at the bottom of the stream. “Macro” means they’re big enough to see with the naked eye. And “invertebrate” describes animals that lack a backbone.

Heads Up!

Always get an adult’s permission before wading into a stream.

Here's What You Need

• Aquarium dip net or kitchen sieve
• White ice cube tray
• Tweezers
• Magnifying glass
• Rubber boots or wading shoes

Here's What You Do

• Find a riffle. This is an area where shallow water tumbles over rocks. The water picks up oxygen as it splashes. Because all creatures need oxygen, lots of macroinvertebrates live in riffles.
• Set your net. Place your dip net or sieve in the riffle and stand upstream.
• Do the benthic boogie. Shuffle your feet in the stream gravel and scrub rocks with your hands. This will dislodge creatures clinging to the rocks, and some of them will flow into your net.
• No riffle? No problem. Search along the stream bank where plant roots dangle into the water. Place your dip net downstream from a root mat and kick water through the roots to dislodge creatures hiding inside.
• Sort your catch. Use tweezers to gently pick macroinvertebrates out of your net. Place them in a white ice cube tray filled with water from the stream. Use the Creepy-Crawly Guide to identify what you’ve caught.
• Set them free. When you’re done observing your catch, return the creatures to the place where you collected them.

Creepy-Crawly Guide

Pollution Sensitive

• Stonefly
• Caddisfly
• Hellgrammite
• Riffle beetle
• Gilled snail

Somewhat Sensitive

• Dragonfly
• Scud
• Crane fly
• Mussel
• Crayfish

Not Sensitive

• Aquatic worm
• Leech
• Black fly
• Midge fly
• Pouch snail

Join a Stream Team!

If you love good fishing, clean water, or simply splashing around in a stream, join a Stream Team! As part of the team, you’ll pitch in to pick up litter, test water to make sure it’s clean, or help with many other fun activities to protect your local waterway. To learn more, wade over to mostreamteam.org.

Caddisfly in the Coal Mine

Some macroinvertebrates are so sensitive to pollution that they live in only the cleanest of streams. Others can handle a little pollution, but not much. And some aren’t that sensitive to pollution and will survive in everything from pristine to filthy water.

If you catch lots of pollution-sensitive macroinvertebrates, your stream is probably healthy. But if all you find are critters that aren’t sensitive to pollution, your stream may need a clean-up.