A silkworm is not a worm; it is the caterpillar of a moth called Bombyx Mori.

The caterpillar of the silkworm makes its cocoons of a much stronger silk than the ordinary caterpillars that we see in our yards and gardens.  This discovery was made thousands of years ago by the Chinese.  The Chinese wove the silk from the cocoons into beautiful soft materials.  Over the years, the silk farmers let the caterpillars that made the largest cocoons, to turn into moths.  The moths then laid eggs and the eggs hatched out more caterpillars  making even bigger cocoons.  Over the centuries, the size of the cocoon has increased and silkworm cocoons are now much bigger than the cocoons of other caterpillars.  At least half a mile of continuous thread may come from one cocoon.

The silk farmers keep the silkworms in large, shallow wooden trays in a warm room and they are fed every day.  If they are fed from fresh mulberry leaves the silk is the best.

The glands near the caterpillar's mouth produce the silk. The soft, sticky silk is pushed out like toothpaste squeezed from a tube.  When it reaches the air it hardens.  The caterpillar then attaches the strand to a twig or leaf while it is still sticky and then wraps the strand round and round its body using its mouth and twists its body about until it is inside a cocoon of silk.    Each layer is glued together and the whole thing becomes hard and strong.  The caterpillar then turns into a pupa inside its cocoon.  The silk farmers bake most of the cocoons but some are saved so that they can turn into moths.  The cocoons are put into hot water to soften the glue that they produce and the strand is unwound by special machines, which twist several of them into long threads of silk ready to be woven into lengths of silk material.