Victor Dorsen, age 12, of Longview, Wash., for his question:

WHAT IS USED TO MAKE A COCOON?

A cocoon is a protective covering that encloses the pups of many insects. The mature larva prepares the cocoon as a shelter around itself. Inside the cocoon, the larva changes to a pupa and eventually transforms into an adult insect. The chief substance of most cocoons is silk.

Among the insects that spend part of their lives in cocoons are ants, wasps, bees and moths. Spiders spin silk cocoons around their eggs to protect them.

But all cocoons are not made of silk. Often the larva produces other substances from which it builds a cocoon. It may also use hairs from its own body, wood pulp, earth or grains of sand. Some creatures use little or no silk in constructing their cocoons.

Most moth caterpillars (larvae) form cocoons. But many pass the pupal stage in the soil without a protective covering.

A few butterfly caterpillars make only flimsy cocoons.

Perhaps the best known cocoon is that of the domestic silkworm, which supplies most commercial silk. Some tussah silk obtained in India comes from the cocoons of large emperor moths.

Most moth caterpillars build their cocoons in inconspicuous places. They may choose a place under loose boards, beneath the bark of a tree or among dead leaves or trash.

Ceropia, Promethea and Cynthia moth larvae build large cocoons that they fasten to tree twigs. These can easily be found in the winter when the trees are bare.

The pupae of most moths spend the winter inside the cocoon. But the larva of many other kinds of moths does not change into a pupa until spring. The wooly bear caterpillar, the larva of the tiger moth, builds its cocoon in the spring. Still other kinds pass the winter in the egg stage or as partly grown larvae.

Every butterfly goes through four stages of life: egg, larva (caterpillar), pupa and adult.

A few days after a female lays butterfly eggs on a plant leaf, the larvae or caterpillar starts to form. After the caterpillar grows large enough, it breaks out of the shell. The eggs of some butterfiles hatch in a few days, but others take months.

The caterpillar or larva has a head and a long jointed body made up of 12 parts called segments. It grows fast, shedding its skin four or five times as it becomes larger and larger.

After it has reached full growth the larva finds a place to turn into a pupa, its next stage of life. It is at this stage that the cocoon is formed.

In the cocoon, the pupa does not eat and is almost completely inactive. But inside the shell, the greatest changes of the whole process of metamorphosis take place. The structures of the caterpillar change to those of the butterfly. These changes sometimes may take place in less than 10 days, but usually take longer. Many kinds of butterflies spend the winter in the pupas stage. They may be pupae for six or eight months or more.