Caddisfly is any of a large group of mothlike insects that live in and around water. Adult caddisflies have two pairs of wings that extend over their abdomens like a tent when at rest. Fine, hairlike structures cover the wings. Most adults have brownish or grayish coloring and grow up to about 11/4 inches (3 centimeters) long.
Adult caddisflies are weak flyers that become most active at night. They have poorly developed mouthparts. Instead of eating solid food, they sip water, plant juices, or honeydew (a liquid produced by certain insects).
Caddisfly larvae (young) resemble caterpillars. They live mainly in lakes, rivers, and other bodies of fresh water, absorbing oxygen through threadlike gills on their abdomens. A few species live on land. Unlike the adults, the larvae consume solid food. Most species eat plants or scavenge for meat. These species build portable protective cases in which to live. To make the cases, they glue together sticks, stones, leaves, or sand grains with a silklike substance produced in their bodies. Some caddisflies spin silklike webs or tunnels in the water that both provide shelter and trap prey.
Caddisfly larvae serve as food for fish and other water animals. People often use the larvae as fishing bait. Most caddisflies are sensitive to polluted water, and biologists use them to assess water quality.
