The typical cocoon of the species
is that spun on a fence or outbuilding, not the slender work on
the alders or the elaborate quarters of the bridge. On a board
the process is to cover the space required with a fine spinning
that glues firmly to the wood. Then the worker takes a firm grip
with the anal props and lateral feet and begins drawing out long
threads that start at the top, reach down one side, across the
bottom and back to the top again, where each thread is cut and
another begun. As long as the caterpillar can be seen through
its work, it remains in the same position and throws the head
back and around to carry the threads. I never thought of
counting these movements while watching a working spinner, but
some one who has, estimates that Polyphemus, that spins a cocoon
not one fourth the size of Cecropia, moves the head a quarter
of a million times in guiding the silk thread. When a thin webbing
is spun and securely attached all around the edges it is pushed
out in the middle and gummed all over the inside with a liquid glue
that oozes through, coalesces and hardens in a waterproof covering.
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