What's That Bug? does not endorse extermination

Cocoon with raised circular bumps
March 28, 2010
Hello Bugman, from across the pond. I spotted this cocoon, attached to a branch of a 2 year old Hebe, and can’t find out what it is. It’s about the size of my thumb, but fatter – completely secured along it’s length to the branch, and looking very solid. The small circles on the outside are almost like little hatched eggs – these have confused me, as whatever is inside would have had to crawl in after making them, rather than spinning a cocoon around itself? It is as if it needed extra armour. Inside is something which is filling the whole cavity, and looking a bit furry 🙂
Luigi
Surrey, South East England

Rusty Tussock Moth Cocoon and Eggs

Hi Luigi,
This is a most interesting situation.  Before we saw your location was England, we were certain that this must be a Cecropia Moth Cocoon.  It is actually a Small Emperor Moth Cocoon, Saturnia pavonia, which can be viewed on the Moths and Butterflies of Europe and North Africa website.   Eggs are typically laid in neat rings around the twigs of the food plant, and it seems like the moth that emerged from this cocoon was a female and she laid her eggs on her own cocoon.  We are going to contact Bill Oehlke with this unusual situation and he may request permission to post the photos on his own website.

Rusty Tussock Moth Cocoon and Eggs

Correction:  Rusty Tussock Moth Eggs and Cocoon
March 28, 2010
Hello,
These are not the eggs of a saturniid but rather the rusty tussock moth (Lymantriidae: Orgyia antiqua), which is native to Europe but is now found throughout North America and elsewhere.  It is typical of this species and a number of other tussock moths for the eggs to be deposited right on the female’s cocoon, because the females are flightless.
There is a photo similar to these in my new book, “Tracks & Sign of Insects and Other Invertebrates,” which I think y’all might enjoy.  There is some information about it here: http://www.northernnaturalists.com/invert_tracks.html
Cheers,
Charley

Ed. Note:
We found a matching photo on Wikipedia.

Thank you so much for your reply – that’s really interesting.  I’ve just had another look at it, and there is definitely something still inside the cocoon, so the moth has not yet emerged (I see that the UK flight time starts in mid-April).  I haven’t noticed any larvae of the kind, and no larvae damage to the plant (a Hebe). I wonder if something else entirely has laid its eggs on this cocoon?

What's That Bug? does not endorse extermination

3 Responses to Rusty Tussock Moth Cocoon and Eggs from England

  1. Hello,

    These are not the eggs of a saturniid but rather the rusty tussock moth (Lymantriidae: Orgyia antiqua), which is native to Europe but is now found throughout North America and elsewhere. It is typical of this species and a number of other tussock moths for the eggs to be deposited right on the female’s cocoon, because the females are flightless.

    There is a photo similar to these in my new book, “Tracks & Sign of Insects and Other Invertebrates,” which I think y’all might enjoy. There is some information about it here: http://www.northernnaturalists.com/invert_tracks.html

    Cheers,

    Charley

  2. darlene R says:

    I live in Northern California and was dewebbing the school when I found 2 of these egg covered cocoons, I have one at my home and the other is still on the school.
    Are these bad for the environment here or should they be removed from the school.

    This the only place I have found this cocoon picture.

    Sincerely
    Darlene

    • bugman says:

      We would be more inclined to guess you encountered the eggs of a related native species, perhaps a Vapourer. We are more inclined to eliminate invasive species than native species, but it is still possible for native species to create a problem in a home garden, though they generally have predators that help to keep populations in check. We will leave the decision up to you.

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