David Tsosie, age 10, of Ft. Wingate, N.M., for his question:

HOW MANY YARDS OF SILK DOES A SILKWORM SPIN?

It takes many silkworms to spin enough silk to weave one yard of silken fabric. But each little grub does his very best, which is not bad at all. Actually he spins his thin, silken thread in a single strand. And its total length is about one half a mile long  which tots up to 880 yards.

In our country, a small family business may be keeping worms, rabbits or bees. In certain other countries, a popular family business is keeping silkworms. It must be a place where plenty of the right mulberry trees grow and where the weather is just right, not too hot or too cold, too damp or too dry. For these little silk spinning caterpillar insects are very fussy. Actually, people have pampered them for so long that these silkworm moths can no longer survive alone in the wild.

Tending silkworms to gather their silken threads began in China more than 4,000 years ago. Later, the idea was adopted by the Japanese, who now produce most of the world's silk. Usually the family business starts in the spring with one ounce of silkworm eggs. The eggs hatch into about 40,000 grubby little caterpillars. For the next 30 days, the famished caterpillars devour a ton of freshly picked mulberry leaves.

Then their caterpillar stage is over and each spins a long thread of superfine silk to weave a soft blanket around himself. The total crop yields about 130 pounds of these silken cocoons, which may produce 12 pounds of raw silk.

Each cocoon is a single thread, perhaps half a mile long, woven around and around in figures of eight. Inside, the pupa is changing into an adult silkworm moth. When this job is done, if something is not done to stop him, the moth will chew his way out, cutting the long thread into countless pieces, too short for weaving. so the cocoons are baked to destroy the insects inside them.

Tenderly the single threads are unwound, twisted and spun into weavable strands. It takes but a few ounces of the precious silk to make one yard of fabric  and several thousand silkworms were needed to provide the raw material.

During their busy lifetime of 30 days, the famished silkworm caterpillars are kept on trays in an airy, warm, dry room. Meals of fresh mulberry leaves must be served on time, and during his last nine days each caterpillar devours twice his weight every day.