Robert M. McClung, Aquatic insects and how they live, New York, William Morrow, 1970,
CADDISWORMS, THE BUILDERS
Sometimes you may see what looks like a little bundle of sticks crawling along the bottom of a stream. Pick it up, and you will discover that the bundle is really a tube, or a case, with an insect inside it. What you have is a caddisworm- the larva of an order of mothlike aquatic insects called Trichopetera, meaning “hairy wings.”
The leaf-eating caddis larva looks a lot like a caterpillar, except that it has gills on its abdomen and has no fleshy legs. It does have a pair of drag hooks at the rear end of its body. The drag hooks anchor the larva within the case.
Many Kinds of Shelters
Pratically all the caddisworms construct cases, or shelters, which they carry about with them wherever they go. The case helps to protect the soft-bodied larva from fish and other enemies.
A particular kind of caddisworm often may be identified simply by the kind of case it makes. Each species uses a specific type of building material and constructs the case in a distinctive way.
Some caddisworms build shelters like log cabins, using tiny twigs or plant stems bound together with silk. Others use leaves as their principal building material. Several of them cut leaf pieces that are rectangular or almost square, then fasten them together in successive rings. Another binds long, narrow leaf pieces together in a continuing spiral.
Some caddisworms use small pebbles to construct stone shelters. Several make smooth tapering tubes of fine sand, and one fashions its sand shelter in the shape of a spiral snail shell, about a quarter of an inch long.
Experiments with Caddisworms
You can easily keep most kinds of case-building caddisworms in small bowls or jars, and watch them while they work. Take a larva out of its case, then supply it with building material and watch it construct a new case.
Do not try to remove the larva from the front of its old case, however, for it holds onto the rear part of the case with its drag hooks very firmly. Instead, gently poke a smooth blunt probe into the rear of the case, and the larva usually humps its way out of the front as quickly as possible.
Try giving one caddisworm some of its natural building material. Then, for comparison, give another larva some different material- coloured paper, tiny beads, cellophane- and see what each will do.
If two caddisworms are put into a bowl, together with one empty case, each larva heads for the shelter and tries to occupy it. The loser then may try to dislodge the winner by entering the case from the rear. If he succeeds, the ousted larva soon tries the same thing. Many times their positions will be reversed again and again.