While they make an oak tree look a bit unsightly, orange galls don't harm the tree itself and are actually best left alone.
Fuzzy orange galls like this are common on oak leaves. They are caused by the leaf's reaction to a tiny wasp egg. Credit: Courtesy of Terri Umble

This story was originally published in September 2020.

Orange galls, fuzzy galls or fuzzy orange galls, no matter what you call them if you have an oak tree in your yard or on your property you likely have them. The culprit is the Cynipid wasp, a tiny member of the Vespidae family that lays its eggs on oak tree leaves.

“The gall is the plant or tree’s reaction to the insect’s egg,” said Jim Dill, pest management specialist with the University of Maine Cooperative Extension. “The leaf tissue grows around the wasp egg.”

Orange galls then serve as a protective shell in which the wasp larvae can grow and feed, Dill said.

In the case of the fuzzy orange galls, these growths look like tiny balls of fluff. Early in the summer, they are a light tan. As the season goes on they start to darken until in late August and September they are deep orange and brown.

Around that time orange galls, with the wasp larvae inside, fall off the leaf and the wasp will burrow into the ground until it pupates. It’s a lifecycle that can last one or two years, Dill said.

While they make an oak tree look a bit unsightly if there are a lot of orange galls on the leaves, Dill said they do not harm the tree itself and are actually best left alone.

“You probably would do more damage to the leaf scraping it off than the gall is doing,” Dill said. “It’s just sitting there on top of the leaf and the leaf is still able to do its thing with photosynthesis.”

The adult wasp is just as benign, Dill said, adding that it’s doubtful people will even see them.

“They are so small, smaller than a blackfly or fruit fly,” he said. They are so tiny I doubt you would even pay attention to one.”

Cynipid wasps feed on plant nectar and don’t sting people or animals.

“They basically just flit around looking for a mate,” Dill said.

Julia Bayly is a reporter at the Bangor Daily News with a regular bi-weekly column. Julia has been a freelance travel writer/photographer since 2000.