This is the rule with all
Promethea cocoons I ever have seen. Polyphemus selects a cluster
of leaves very frequently thorn, and weaves its cocoon against
three, drawing them together and spinning a support the length of
the stems, so that when the leaf is ready to fall the cocoon is
safely anchored. When the winter winds have beaten the edges from
the leaves, the cocoon appears as if it were brown, having three
ribs with veins running from them, and of triangular shape.
Angulifera spins against the leaves but provides no support and so
drops to the ground. Luna spins a comparatively thin white case,
among the leaves under the shelter of logs and stumps. Io spins so
slightly in confinement that the pupa case and cast skin show
through. I never have found a pupa out of doors, but this is a
ground caterpillar.
Sometimes the caterpillar has been stung and bad an egg placed in
its skin by a parasite, before pupation. In such case the pupa
is destroyed by the developing fly. Throughout one winter I was
puzzled by the light weight of what appeared to be a good Polyphemus
cocoon, and at time for emergence amazed by the tearing and
scratching inside the cocoon, until what I think was an Ophion
fly appeared.
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