I was snorkeling in shallow water in a small lake in central Massachusetts today, and saw an interesting creature. What caught my eye was that a small section of the sandy gravel on the lake bottom was moving. It scooted forward about an inch (2.5 cm) and stopped. Then it did it again. I picked it up gently and turned it over to investigate. It was about 3/4 of an inch (2 cm) long and about 1/2 an inch (1 cm) wide. It was made of grains of sand and gravel glued together. Attached underneath was a small tube. The creature who lived in the tube had withdrawn and couldn’t be seen, but I knew what it was: the larvae of one of over 4,000 species of caddisflies. Most caddisfly larvae construct houses, which they use for disguise and protection. Each species uses characteristic materials and design. The resulting shelters range from a small tube of reed or grass, to houses constructed out of sand in the shape of a snail shell. Other caddisflies actually glue tiny snail shells together. Most caddisfly larvae graze on algae and other plant material. Eventually, they leave the water and metamorphose into a somewhat moth-like adult. Caddisflies are, in fact, related to butterflies and moths. The pictures below show some of the diversity of caddisfly larvae homes. Unfortunately, none looks quite like the one I saw, and I didn’t have a camera, but a couple show homes constructed of gravel.

Caddisflies are often used in evaluating the health of streams. Most species are not tolerant of pollution or silted water, so to find a healthy collection of caddisflies in a stream is a good sign.

What I find most amazing about caddisflies is that they are able to construct such clever, effective and attractive homes with such a tiny brain. Incredible.

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