Galls are swellings or growths caused by the secretions of certain insects such as cynipid wasps.  The galls may be incorporated into the plant tissue, such as on a twig, or attached to it.  On twigs, galls may disrupt the movement of water and food, resulting in the death of the twig beyond the gall.  Twig galls are not regarded as a serious pest of trees, but do result in localized twig and branch dieback that may appear alarming.  There are many types of twig galls and galls are also found on other plant parts including leaves, petioles, and acorns.   

gall art

More information about oak galls in general (not specific to Oregon)

Gall wasps (see P. 28 in A Field Guide to Insects and Diseases of California Oaks)

More information about insect galls


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