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Elm Cockscomb Gall

Galls, abnormal plant growths caused by a variety of agents including insects, come in myriad sizes, shapes and colors.  One of the most distinct is the Elm Cockscomb Gall which is caused by an aphid (Colopha compressa).  These galls, named for their striking resemblance to a rooster’s comb, are maturing and turning red this time of year. 

For much of the summer the aphids responsible for these galls live underground sucking sap from grass roots.  In the fall a new (sexual) generation is born, takes to the air, mates and heads for an American Elm (Ulmus americana) tree where each female aphid lays a single egg under the bark.  In the spring the emerging nymphs seek young American Elm leaves on which to feed.  As they do so, the aphid nymphs emit compounds that result in the formation of galls.  Each nymph matures inside a gall and then reproduces asexually, giving birth to hundreds of young within the gall.  The mature, reproductive adult aphid dies and the young aphids develop into winged adults that exit the cockscomb gall through a slit on the undersurface of the leaf.  These aphids then go down into the soil to feed on the sap of roots until the next generation is born.

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4 responses

  1. Oh my. Another wonder – what a life story!
    I don’t notice many (any, actually) elms around here in Worcester (VT), though I can’t say that I’ve been looking for them. But I do remember their graceful profile from all the elms I saw in my youth, and I think I’d notice. I’m wondering where they are making a significant comeback?

    July 9, 2021 at 8:50 am

  2. Amazing. Evolution is incredible.

    July 9, 2021 at 9:33 am

  3. Alice

    Incredibly interesting. I think I’ve only seen oak galls.

    July 9, 2021 at 10:08 am

  4. I’m not sure what we have around here! We end up with a very round ball, about the size of a Jax Ball. A green ball, inside it sort of looks like a apple! Mostly on Oak Leaves. If there are parasites or other insects inside they are not visible to the naked eye! I Was truly was expecting to see a worm inside! Nope! Thank you though once again for something very interesting! 🙂 ❤

    July 9, 2021 at 12:57 pm

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