Having attained full growth, the worm is ready to spin its cocoon. It
loses its appetite, shrinks nearly an inch in length, grows nearly
transparent, often acquiring a pinkish hue, becomes restless, seeks
a quiet place or corner, and moves its head from side to side in an
effort to find objects on which to attach its guy lines within which
to build its cocoon. The silk is elaborated in a semi-fluid condition
in two long, convoluted vessels or glands between the prolegs and
head, one upon each side of the alimentary canal. As these vessels
approach the head they grow more slender, and finally unite within the
spinneret, a small double orifice below the mouth, from which the silk
issues in a glutinous state and apparently in a single thread.
[Illustration: COCOON BEGUN--SILKWORM CAN STILL BE SEEN.]
The color of the worm’s prolegs before spinning indicates the color the
cocoon will be. This varies in different species, and may be a silvery
white, cream, yellow, lemon, or green.
[Illustration: COMPLETED COCOON.]
~WHEN THE SILKWORM’S WORK IS DONE~
When the worm has finished spinning, it is one and a quarter inches
long. Two days later, by a final molt, its dried-up skin breaks at the
nose and is crowded back off the body, revealing the chrysalis, an oval
cone one inch in length. It is a light yellow in color, and immediately
after molting is soft to the touch. The ten prolegs of the worm have
disappeared, the four wings of the future moth are folded over the
breast, together with the six legs and two feelers, or antennæ. It soon
turns brown, and the skin hardens into a tough shell. Nature provides
the cocoon to protect the worm from the elements while it is being
transformed into a chrysalis, and thence into the moth.
[Illustration: MOTHS EMERGING FROM COCOONS.]
With no jaws, and confined within the narrow space of the cocoon, the
moth has some difficulty in escaping. After two or three weeks the
shell of the chrysalis bursts, and the moth ejects against the end of
the cocoon a strongly alkaline liquid which moistens and dissolves
the hard, gummy lining. Pushing aside some of the silken threads and
breaking others, with crimped and damp wings the moth emerges; and the
exit once effected, the wings soon expand and dry.
[Illustration: COCOONS FROM WHICH THE MOTHS HAVE EMERGED.]
The escape of the moth, however, breaks so many threads that the
cocoons are ruined for reeling, and consequently, when ten days old,
all those not intended for seed are placed in a steam heater to stifle
the chrysalis, and the silk may then be reeled at any future time.
The moths are cream white in color. They have no mouths, but do have
eyes, which is just the reverse of the case of the worm. From the time
it begins to spin until the moth dies, the insect takes no nourishment.
The six forward legs of the worm become the legs of the moth. Soon
after mating the eggs are laid.
The male has broader feelers than the female, is smaller in size, and
quite active. The female lays half her eggs, rests a few hours, and
then lays the remainder. Her two or three days’ life is spent within a
space occupying less than six inches in diameter.
One moth lays from three to four hundred eggs, depositing them over an
even surface. In some species a gummy liquid sticks the eggs to the
object upon which they are laid. In the large cocoon varieties there
are full thirty thousand eggs in a single ounce avoirdupois. It takes
from twenty-five hundred to three thousand cocoons to make a pound of
reeled silk. Do you wonder that, centuries ago, silk was valued at its
weight in gold?
Growers of silk in the United States, by working early and late every
day during the season, which lasts from six to eight weeks, could
scarcely average fifteen cents for a day’s labor of ten hours. Silk,
once regarded as a luxury, is now considered a necessity.
[Illustration: HOW THE COCOON IS UNWOUND