Insect Galls in Trees

Insect galls are abnormal growths that occur in trees or other plants. These galls (which fall into the wider category of plant galls) can be caused by fungus, bacteria, nematodes, and mites, but are most often caused by insects.

  1. Function

    • Insect galls can vary in appearance depending on where they're found, but serve the same purpose--providing nutrition and habitat for developing insect larvae. These larvae, according to entomology.ifas.ufl.edu, feed on the gall tissue during their development before eventually emerging from their galls around adulthood.

    Species

    • Most gall-dwelling insects are either gall gnats or gall wasps. According to entomology.ifas.ufl.edu, 1,500 of the 2,000 gall-producing insects in America fall into these two categories. Also mentioned is the cypress twig gall midge, which makes its gall on cypress trees.

    Are They Dangerous?

    • Galls do not often harm the plants on which they're found. Plants already in trouble are the ones hit hardest by the formation of galls and their subsequent guests. However, most plants coexist quite well with their insect guests.

    Uniqueness in Galls

    • For every gall-producing insect, there is a uniquely noticeable gall to go with it. This means that for every type of insect which produces galls, that insect's galls will be different in appearance from those of another insect.

    Size and Appearance

    • Galls can run from 2 inches in diameter to being so small they're nearly invisible to the naked eye. They don't always have the same shape, either. They can appear as tubes, spheres or simply as abnormal growths. They can be covered in tiny hairs, spines, or have nothing on their surface at all.