Piece of worsted yarn

Mary R. Berenbaum, Ninety-nine Gnats, Nits and Nibblers, Ill. John Parker Sherrod, Urbana & Chicago, University of Illinois Press, 1989, p. 185.

Caddisworms are caterpillar-like aquatic insects that construct an assortment of portable cases in whic to house and protect themselves. The word «  caddis » is derived from a Middle English term referring to bits and piece of worsted yarn. Caddisworms are more likely to use stones, sand, pebbles, or twigs to construct their houses and use silk to hold it all together.

The cases are so distinctive that caddisworms can be recognized and identified by the case alone. For example, micro-caddisflies (in the family Hyrdroptilidae) make tiny cases like purses (only in their later instars) that average a quarter-inch in length. The Phryganeidae, or large caddisflies (the largest of the group), make cylindrical cases up to two inches long with sticks and leaves in a spiral arrangement. The Limnephilidae are called the log caddisworms because of their habit of using sticks and leaves in crosswise construction to build a case, although some members of the family, marching to a different drummer, construct horn-shaped cases out of tiny bits of sand and shell painstakingly plastered together with strands of silk. And some psychomyiids make subterranean fallout shelters by lining burrows in the sand of stream bottoms with a cementlike substance. Then there are the philopotamids, which spin long fingerlike tubes out of silk. Mosty in keeping with the Halloween spirit, however, are the Helicopsychidae ; tese caddisworms arrange tiny sand grains into a helical case that’d a dead ringer for a snail shell.