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Bruce Spanworm Moths Emerging

11-17-17 hunter's moth IMG_4508

If you’ve walked in northern New England woods recently, chances are great that you’ve noticed light tan moths with a one-inch wing span flitting about — with temperatures in the 20’s, this seems slightly incongruous. However, there are some insects that are active in cool weather, among them the Bruce Spanworm Moth (Operophtera bruceata), also called Winter Moth and Hunter Moth (these moths are active during deer hunting season, which approaches winter). The adults of this species are active from October to December.

Bruce Spanworm Moths belong to the Geometer family, the second largest family of moths in North America. All the flying moths you see are males seeking wingless, and therefore flightless, females to mate with. The females crawl up the trunk or branch of a tree and send out pheromones to attract winged males. After mating, the female lays her eggs which hatch in the spring. Larvae pupate in the summer and adult moths emerge in the fall.

Many Geometers are considered agricultural and forest pests. Bruce Spanworm larvae periodically defoliate hardwood trees, preferring the buds and leaves of Sugar Maple, American Beech and Trembling Aspen trees. In 1958 in Alberta, Canada, at the peak of a 10-year infestation, over 50,000 acres were moderately or heavily affected by Bruce Spanworm larvae.

9 responses

  1. Alice Pratt

    So similar in mating habits….looking for wingless females….as the Gypsy Moths….they are easy to catch, on the side of a house or window by pinching their wings together & then in a jar of soapy water….hope it doesn’t sound too cruel, but a vacuum works well. They love Weeping Cherry Trees, as well. ☹️

    November 17, 2017 at 7:40 am

  2. Gwyneth Loud

    Hi Mary,
    I think the Winter Moth is Operophtera brumata, just slightly different from the Bruce Spanworm Moth. My brother, Joe Elkinton, who heads up the wWnter Moth research at U Mass. says that the two can only be IDed by examining their genitalia under the microscope.!
    Best,
    Gwyn

    November 17, 2017 at 7:48 am

    • Thank you, Gwyn!

      November 17, 2017 at 5:41 pm

    • the problem with common names. our winter moth is the bruce spanworm, and the other winter moth is the “bad” invasive one. same name. both are Operophtera. O. brumata is the invasive one, still unreported in Vermont. But I have one that I have kept and have full photos of and I worry it is O. brumata here in northern VT. I sure hope I’m wrong.

      November 17, 2017 at 6:08 pm

  3. Alan M Stoops

    I’ve long been puzzled by insects that have wingless females and winged males. Seems it would make more sense to have winged females, which could spread their eggs farther from their own hatching spot.

    November 17, 2017 at 8:33 am

    • Maybe the females are saving their energy for egg-making???

      November 17, 2017 at 5:41 pm

  4. How is it that a wingless insect may be classified as a moth? Just because its mate is a moth?

    November 17, 2017 at 9:17 am

    • Good question, Molli. One which I do not immediately know the answer to, but I think you’re on the right track.

      November 17, 2017 at 5:43 pm

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