Green Scene Blog: Why care about the caddisfly?


Dear readers, this post is by Rose Brown, who heads up StreamWatch. As such, she’s well acquainted with some of the inhabitants of our landscape that may have escaped your notice. Here, she makes an introduction.

If you’re driving around the Rivanna watershed this spring, you might spot some StreamWatch volunteers monitoring our local streams. When you’re crossing a bridge, peek down at the stream and look for happy people in waders, holding a net or maybe some tweezers. They’re out there catching and counting the insects and other critters that live on the bottom of the streams because the bugs that we find help to tell the story of how healthy our streams are.

A lot of the bugs that we monitor live their larval stage in the stream and then emerge as flying adults—like dragonflies, damselflies, and mayflies. Another example is the caddisfly. Caddisfly larvae have been making their living on the bottom of the streams for almost 200 million years. Some caddisfly larvae walk around scraping food from the rocks, some shred leaves, some set up a net to catch food in the current, and others hunt smaller invertebrates.

Caddisflies do their best to blend into the bottom of the stream, to avoid becoming someone else’s meal. Some caddisflies even build tiny cases that they carry around as protection. Some make cases of rocks, sand, sticks, or pine needles. Some use leaves that they have cut into precise squares or circles with their mouths. Some cases are built like a horizontal tube-shaped log cabin, others are triangular in shape, and some are made with perfect tiny pieces of gravel that are glued so strongly together that you can’t smash them with your fingers or tweezers … not that you should try! It takes casemakers about a month to build their little homes, and they require constant upkeep.

Caddisflies, along with mayflies and stoneflies, are particularly sensitive to pollution in their environment, so they are our primary indicators of water quality. When we’re out sampling a stream, we’re always pleased when we find these delicate, complex, ancient critters.

To learn more about caddisflies and some of the other invertebrates that we monitor, visit our site.