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Promethea Pupae Parasitized

12-21-15 promethea cocoon 257Although a lack of snow makes tracks difficult to find, there are other, more permanent, animal signs such as bird nests and cocoons that are visible this time of year. Among the more obvious is the cocoon of the Promethea Moth – a giant silk moth. When the time for pupating arrives the Promethea caterpillar selects a leaf and strengthens its attachment to the tree by spinning silk around the petiole of the leaf as well as the branch it grows on (to assure that it doesn’t fall off the tree). With more silk it rolls the leaf up into a tube and then proceeds to spin its cocoon inside the rolled-up leaf, leaving a valve-like structure at the top of the cocoon through which the adult moth exits in the spring.

Unfortunately for silk moths, many are parasitized by flies and wasps (there are nearly 100 natural parasites that affect the 24 species of silk moths east of the Mississippi River). Frequently flies or wasps lay their eggs in silk moth caterpillars and then develop inside them. Eventually the fly or wasp larva secretes a substance that causes the caterpillar to pupate, at which time the fly or wasp also pupates and then exits the moth pupa and cocoon (see exit hole in smaller photo), causing the death of the moth pupa. Silk moth populations are decreasing, in part as a result of these parasitoids. Among others, a non-native parasitic tachinid fly, Compsilura concinnata, is wreaking havoc on silk moths.

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8 responses

  1. Marilyn

    I feel very sad for the silk moth.

    December 21, 2015 at 8:49 am

  2. I always look out for Promethea and Cecropia moth cocoons during the late fall and winter. Usually I spot 45 or 50 of them at least. This season so far I have seen NONE. I wonder why. I miss them.

    December 21, 2015 at 8:59 am

    • Where do you live? 45 or 50 – that’s amazing!

      December 21, 2015 at 6:23 pm

      • the thriving moth metropolis of Adamant, VT – town of Calais.

        December 21, 2015 at 9:53 pm

  3. Kathryn

    It’s a very hard life for small creatures. Poor moth.

    December 21, 2015 at 9:17 am

  4. Cindy

    Wow! The life and death battles going on all around us and most of us have no idea! Thank you.

    December 22, 2015 at 7:39 am

  5. peggy longley

    Our farm once produced silk and I wonder if this northern clime species can be raised to produce silk?????

    December 27, 2015 at 6:47 pm

    • That’s fascinating, Peggy. I don’t know the answer to your question, but I think the introduced silkworm feeds on mulberry, which grows here.

      December 28, 2015 at 3:23 pm

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