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Oak Leaf Galls


Galls are irregular plant growths which can be stimulated by the reaction between plant hormones and powerful growth regulating chemicals produced by some insects, mites, nematodes and fungi.  Galls may occur on leaves, twigs, flowers, buds or roots.  Many plants serve as gall hosts, but certain plant groups are more attractive to gall producers than others. The Oak family is by far the most popular (with 805 species of gall makers; the next largest family being the Daisy family, with less than 200 gall makers). Galls on oaks are most often caused by small wasps or midges.

Each gall-making species of insect produces a uniquely shaped and colored gall.  Thus, it is possible to identify the insect within a gall just by noting the appearance of the gall itself as well as what plant it is on.The growth of the galls takes place in the spring. Gall-making insects lay eggs on the host plant, and the insect larva resides inside the gall that the plant forms. The galls provide the insects within them with both shelter and food. Because many oak leaves persist well into the winter, there is still the opportunity to find galls, though some may be lacking residents at this stage, as many insects emerge as adults in the fall after pupating within the galls.

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8 responses

  1. Thanks Mary! Are the little holes in the galls where insects make their exist?

    November 6, 2019 at 8:24 am

    • Hi Barbara,
      Yes, for the most part, the holes in galls are the exit holes of the insects that were living inside the gall. Chickadees and woodpeckers feast on goldenrod ball gall larvae in the winter, and their holes are more ragged and larger than the insect exit holes!

      November 7, 2019 at 10:25 am

  2. Alice

    I had no idea that there are so many species that cause galls to form on oaks or daisies! So much to learn, with you as a guide, Mary!

    November 6, 2019 at 8:27 am

  3. Thanks Mary! I love your connections with every aspect of life we share on this planet. Now, to do our part to make it possible for ALL life to continue.

    November 6, 2019 at 8:34 am

  4. Heidi Mack

    Hello Mary –

    See mystery bone recently found in below photos – by my daughter’s co-workers on a field trip. Any clues?

    Thanks, Heidi Mack

    November 8, 2019 at 7:54 am

  5. Laurie

    So then is the gall actually composed of plant cells/tissue exclusively? Besides of course the residents.

    November 12, 2019 at 8:17 am

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