Shawn Knox, age 12, of Sioux City, Iowa, for his question:

Does a caddisfly build itself a home?

In its youthful larva stage, the caddisfly does indeed build itself a home. The average adult insect somewhat resembles a brown moth with extra long, skinny antenna and thin wings that can be folded to her sides. She is rated as an aquatic insect because her egg, larva and pupa stages of life are spent in the water. Our 200 or so native caddisfly species build their remarkable personal homes in ponds and streams.

The caddisfly larva seems to be constructed from the front part of an ant and the long wormy part of a caterpillar. The caterpillar section is covered with feathery little threads that act as gills to extract dissolved oxygen from the water. However, the remarkable body is rarely exposed for interested humans to observe. For the caddisfly larva is a spinner of silken thread. In most species, this is used to construct some sort of protective shell.

The shape and durability of the structure varies. One species builds a portable home with gritty fragments woven into the silken threads. It is a hollow tube of protective armor. Sometimes the larva stuffs his wormy tail inside it and sometimes he carries the whole thing around on his back. Another species cuts up leaves and weaves them into a tube shaped husk. One species uses grains of sand to construct a fancy spiral shaped abode that resembles a snail shell. The narrow.end of the structure is sealed with a fine silken net, which allows flowing water to wash dissolved oxygen over the gills.

One group of caddisfly larvae does not build shells or portable homes. Most of them use their silk to weave nets to trap the tiny aquatic creatures and morsels of waterweed on which these insects feed. One species favors the lower level near the bottom of a stream. The silken net is spread between two rocks and works like a spider web, except that it is not sticky.

Several species weave a funnel shaped web with the wider end placed facing upstream, a clever trick that reduces the need to forage for food. The flowing water washes a variety of edible items right into the pantry. In all species the larvae may live several months before graduating to the pupa stage.

Those that build portable homes spend their sleeping pupa period inside their protective shells. When the remodeling job of metamorphosis is completed, they chew their way out of the shells and wriggle to the surface. There the pupa cases crack apart and the adult caddisflies fly off into their airy environment.

The adults fly by night and survive only long enough to prepare eggs for the next generation. After mating, the female lays 1,000 or so small pale eggs at the edge of a stream or pond. Some species fly low and drop their eggs into the water. The winged parents die after a few days, leaving the future of their species to their aquatic offspring.