Winifred & Cecil Lubell, In a Running Brook, Ill. Winifred Lubell, Chicago, Rand McNally, 1968, p. 22-24.
The case builders
Odds and ends of bits of sticks and stones ! That’s what they looked like to us when we first saw them on the bed of the brook. But we were quite wrong.
They’re caddis cases-protective covering built by the caddis insect which live under water until it is full grown and can fly. At first these cases seem to be only bits of trash, but when you examine them closely you see they have all been neatly glued together-piece to piece, stick to stick, stone to stone, and tiny stick to tiny stone.
You find them under the rocks. They are hollow inside and they fit the caddis like a mummy case, but more loosely. The insect can crawl in and out, and water can flow through, bringing food and oxygen.
They are many types of caddis insects and they are all skillful case builders. They use many different materials, depending on what part of the brooks they live in, and what building materials they find there.
Many of them have sharp mouth parts with which to cut building materials into small rectangular pieces, and all of them produce a sticky substance which they use to glue all the oddds and ends of pieces togeher into a solid case.
Some use sticks ans stones. Some use leaves and grass bits of bark, straw, and pine needles. One type sticks together the shells of tiny snails and clams. Another makes a case out of sand grains which looks so much like a snail shell that it fools you unless you examine it with a magnifying glass. Others make cases of silk that they spin as spiders do. Some build stone corrals, often with compartments where they live together. These are the bright green caddisworms.
The case protects the caddis from other insects and also from the tug of the current in the brook. Where the curent is strong, you find the cases weighted down with small stones. Often there are dozens of them stuck to the sides and bottoms of big rocks to keep them from being washed downstream.
When the current is not so powerful, as in the meadow brook, the cases are usually built of lighter materials such as leaves, bits of stems, and grains of sand. Then the case is light enough so the caddis can poke the front of its body out of the tube and drag the case behind it with its strong, hooked forelegs. It makes you think of a small tractor pulling, a huge log and it’s a strange sight to see these bits of sticks suddently come to life and move around jerkily on the bed of the brook.
Inside the case is an underwater insect that looks a good deal like a worm, but it’s not really a worm at all. It’s the larva, or early stage in the life of an insect, which later changes into a caddis fly with wings and is often mistaken for a moth.
The name larva is an inetresting term because it comes from a Latin word meaning « mask ». A mask is something that conceals, and in a way the winged caddis fly really is « concealed » in the wingless caddis larva. To emerge, it must go through metamorphosis-like the mayfly, but with an extra stage called the pupa. As it grows bigger, in stages, it often has to abandon the old case, which has become too small for its body, and it then constructs a new case to fit.