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Bruce Spanworms Emerging & Mating

11-7-13 winter moth IMG_4880I try not to repeat post topics, but in the past two days the sudden emergence of inch-long, tan moths in the woods has been so dramatic that I couldn’t not mention them. These ghost-like, light tan moths are referred to by entomologists as Bruce Spanworm moths, Operophtera bruceata, named after an entomologist by the name of Mr. Bruce. They are often called Winter Moths, due to the fact that they are one of the latest moths to be seen flying, as well as Hunter Moths, as they share the woods with hunters at this time of year. From October to December Bruce Spanworm moths emerge, mate and lay eggs. While this timing is unusual, it makes sense when you think about it — many birds, their primary predators, have left for their wintering grounds. All the moths you see in the air are males — females are wingless and cannot fly. The females crawl up the trunk or branch of a tree and send out pheromones to attract winged males. After mating, the female lays eggs which hatch in the spring, and the larvae feed on a wide variety of deciduous leaves, favoring Trembling Aspens, Sugar Maples, American Beeches and willows. Periodic outbreaks of these caterpillars can result in heavy defoliation.

NB: “This is easily confused with Operophtera brumata – Winter Moth, which is an introduced species from Europe and an abundant pest in the Northeast. Also easily confused with Autumnal Moth (Epirrita autumnata).” Kent McFarland

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12 responses

  1. Dianne and Ed

    THANKS for sharing this….Just yesterday my granddaughter was outside practicing her baton, when she called me to see this very tiny flying critter…….skitted so quickly that I did not get a good look at HIM. Dianne

    November 7, 2013 at 1:13 pm

  2. K.P. McFarland

    Just a bit of caution here. This is easily confused with Operophtera brumata – Winter Moth, which is an introduced species from Europe and an abundant pest in the Northeast. Also easily confused with Autumnal Moth (Epirrita autumnata).

    November 7, 2013 at 1:31 pm

    • Thanks so much for pointing this out, Kent.

      November 7, 2013 at 2:29 pm

  3. Roseanne Saalfield

    and I might note that this spanworm moth could have evolved with Fagus grandifolia because its leaves stay on the trees straight through the winter, as do those of many of our oaks I know you know that….Roseanne

    November 7, 2013 at 1:39 pm

  4. Bunny

    Thank you for your recent post. Yesterday, I saw so many of these moths in the high peaks of the Adirondacks, NY and wondered what they were.

    November 7, 2013 at 2:44 pm

  5. Robyn Deveney

    As soon as these moths appeared, I thought, “I hope Mary Holland does a post on this!” I was wondering if they are the European or native variety. I’ve heard that even experts find it difficult to tell them apart without dissecting them.

    November 7, 2013 at 3:06 pm

    • You’re right, Robyn. As Kent commented, ”

      Just a bit of caution here. This is easily confused with Operophtera brumata – Winter Moth, which is an introduced species from Europe and an abundant pest in the Northeast. Also easily confused with Autumnal Moth (Epirrita autumnata). “

      November 7, 2013 at 3:54 pm

  6. Susan Holland

    Now I am curious- what does the female moth look like? It is hard to imagine a wingless moth!

    November 7, 2013 at 3:47 pm

    • I tried to photograph two of these moths mating last year, so I could show everyone exactly that — she is very strange looking — the photograph did not come out, but I shall try to have more success this fall and will share it if I succeed!

      November 7, 2013 at 3:53 pm

  7. Dramatic is right–all of a sudden, they are everywhere!

    November 7, 2013 at 4:25 pm

  8. doreen morse

    Beautiful moth…love the way the edges of the wings look like the fringe of a carpet…

    November 8, 2013 at 12:08 am

  9. Audrey Hyson

    Thank you for reminding us about these moths. I too have observed the sudden upsurge in the past few days. I was surprised to see them flying in very low temperatures early in the morning . That seems unusual for an insect.
    Ach

    November 8, 2013 at 1:25 am

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