A bundle of crossed sticks

J.T. Lloyd, The Biology of the North American Caddis Fly Larvae, Cincinnati, Bulletin of the Lloyd Library, 1921.

Perhaps the larvae, or caddis-worms — known also as « stick- worms » — are more familiar to the average layman than the winged adults. Almost every child has seen a bundle of crossed sticks jerkily drawn about through the water by an insect .  with only head and legs projecting. Not all cases, however, are of the cross-stick type, and not all are so familiar to the layman. There are portable cases in almost endless variety of form, and made of almost every material to be found in the water, and there are many larvae that make no portable cases, but live in silken tubes, awaiting animal prey or plancton to become entrapped in their catching nets. A few caddis-worms make no cases at all, but crawl free among the stones. Whether the caddis-worms construct portable cases, or silken tubes, or make no cases until almost time for pupation, they all secrete a glue, or silk, through openings.