Jumping oak gall
Cliff Sadof, Purdue Extension Ornamental Entomology Specialist
Jumping oak galls are bumps that grow on the undersides of oak leaves after a small stingless wasp, Neuroterus saltatorius, lays eggs in the leaf tissue. Each gall contains the tiny worm-like immature stage of the wasp that feeds on the gall during the summer. The gall will fall off the leaf and jump after it hits the ground, in order to help it gain a good overwintering position in the soil or leaf litter. Adult wasps will emerge in the following spring to attack leaves again. According to Phil Marshall, State Entomologist at the Indiana DNR, the first large outbreak was recorded on white oak in southern Indiana in 1999. This resulted in widespread defoliation but the vast majority of trees survived.
Reports of jumping oak galls this past spring suggested that once again another outbreak was occurring on white oaks. The outbreak was short lived with no longterm harm to tree health.
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Images courtesy of Wayne Werne, Forest Resource Specialist, Harrison Crawford State Forest