This winter
I spotted a large cocoon near the top of a birch tree outside my window. It remained attached to a twig through wind
and rain until one day, strong winds finally broke the twig. Naturally I went outside looking for it and
it must have been my lucky day. Not only
did I find it, but I also found an old cocoon with the emergence hole.
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| I glued the cocoon by its penduncle to a branch by my porch. I hope I will be lucky enough to see the moth emerge. |
These large
cocoons are produced by a very large silk moth, the polyphemus moth, Antheraea polyphemus. Caterpillars spin a cocoon connected to a
twig by a sturdy silk attachment called a penduncle. When it is time for the moth to emerge from
its silk case, it must secrete an enzyme (cocoonase) to soften the end of the
thick cocoon. Then, using spurs on its
thorax, the moth turns inside the cocoon in a circular pattern to create an opening.
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| On the left is an old cocoon showing the emergence hole created by the moth. |
The adult emerges
in late afternoon to dry and expand its wings in preparation for an evening
flight to search for a mate. Females
release pheromones to attract a male.
Once mated, the female begins laying eggs and continues to lay eggs for
several nights. These moths only produce
one brood a year. Caterpillars hatch and
spend the rest of the summer eating leaves. Oak, willow, birch, cherry and hickory are among the caterpillar host plants. When fall arrives, they will pupate and overwinter in their sturdy cocoon.
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| Polyphemus moth |
The beautiful
polyphemus moth has a wingspan of four to six inches, with large eyespots. They also have large, feathery antennae. With no mouthparts for feeding, they only
live a few days.
