Subject: Nest Glob in Birch Tree?
Location: Moss Beach, CA, USA
January 8, 2016 3:50 pm
Dear Bugman,
I just discovered this thing in our birch tree. I went up a ladder and took a photo. It is about 4″-5″ tall and about 3″-4″ wide. It looks like it was made with leaves and fibers wrapped around something which are now decayed and attached with little stringy bits at the top and to some small branches. I can’t see an entrance anywhere, but it was up high so I couldn’t see the very top. I haven’t seen any activity going in or out. We are about a block and a half from the ocean, if that helps. I don’t want to cut it down in case it is something that is not harmful. But if it IS harmful, I want it off of there before something creepy, bitey and stingy emerges!
Signature: Christine

Polyphemus Moth Cocoon

Polyphemus Moth Cocoon

Dear Christine,
If you had been located in the Eastern portion of the U.S., we would have been in doubt of the identity of your cocoon, but since the Luna Moth is not a western species, by the process of elimination, we believe this is the cocoon of a Polyphemus Moth.  The caterpillar constructs the cocoon by spinning silk around leaves from the food plant, and sometimes the cocoon remains on the tree and sometimes it falls to the ground when the leaves fall.  We were not certain if birch was a food plant for the Polyphemus Moth, but according to the Auburn University Entomology and Plant Pathology site:  “The larva feeds on the foliage of many species of trees, including oak, maple, basswood, beech, butternut, walnut, birch, yellow-poplar, sassafras, ash, willow, elm, and sycamore. ” 

About fifteen minutes ago I sent a photo of a nest in our birch tree.  I think I may have figured it out.  I started searching a different way and found photos of Giant Silk Moth nests which look very like what is in our birch tree.  Some photos show  holes from a woodpecker and I want your opinion on an idea I have.  I would love to see the moth emerge and was thinking of placing a protective netting  cage around it so it still gets moisture and the cold air it needs and then closely monitor it.  It would be sad if a woodpecker found it and ate the yummy moth inside!
Signature: Christine

Hi again Christine,
A protective netting will help keep out large predators, but you will have to remain diligent and check for emergence on a daily basis.  You might be better off letting nature take its course.

Hello Mr. Marlos,
Thank you for responding so quickly.  I am a housewife and am at home most of the time; the birch tree is just 15′ from our front door and I feed the birds out in the garden.  I can keep a close eye on it.  Maybe I can fashion something with a door so if there is a day when I will be gone for a long time, I can keep it open and hope for the best.  I found a website dedicated to raising them and I now have a pretty good idea of how best to keep it safe, but when it hatches, let it go about its mothy business!  I hope I can get some nice photos!
Thank you,

Location: Moss Beach, California

3 Responses to Polyphemus Moth Cocoon

  1. Ben says:

    Assuming Christine’s measurements are accurate, and based on what I see as more of a spindle shape, I think it’s more likely this is a Cecropia moth cocoon!

  2. Ben says:

    Oops, missed that it was found in California. Possibly Hyalophora euryalus?

    • bugman says:

      Thanks Ben,
      We based the ID on the incorporation of the leaf into the cocoon and the birch food source. Since the cocoon was up a tree a bit, we did not place too much emphasis on the measurements which seem too big to us.

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