The sound of fluttering tiny wings is common in Richmond during the spring and summer. Soon the air will be filled with the familiar buzz of flying fauna — some friendly, some offensive — fattening themselves with the nectar from flowers. For some insects, their entire life history is inextricably tied to plants. They are born in the tissues of a floral host, feeding on, and protected by, peculiar nurseries that resemble tumors erupting from the skin of the plant. These nurseries, called “galls,” take many forms depending on the kind of baby insect that lives in them and the kind of plant they grow on.
Common spangle gall on the underside of oak leaves. Several wasps of the genus Neuroterus make such galls. Credit: Lorne Field
Finding insect galls is common in the spring and early summer and the time for spotting them in Richmond is now. Most galls form year-round but they are largest in the spring before the adults come out.
Gall Wasps are the most common nursery makers. They belong to the Cynipidae family which includes about 1,300 different species worldwide, more than 800 of which are common in North America. Their galls can look like woody warts, green globs and even fuzzy flowers. The shapes, colors and sizes of galls are as varied as the insects that create them. The common unifier is that they are all created by a female insect injecting her eggs into the plant. A mutation forms in the plant tissue, and inside it the developing larvae find nourishment and shelter from predators.
Oaks are the most common hosts for gall wasps, but the intrepid gall-gawker can sometimes find them on maples and roses as well. Before you hastily decide NOT to look for wasps, remember most wasps do not sting. The big stinging wasps (yellow jackets, paper wasps and hornets) make nests out of paper or in the ground. Most gall-builders are tiny and harmless.
Wool sower wasp gall on a white oak sapling. Credit: Lorne Field
One of the most common galls is the “oak apple”, so called because it resembles a round fruit that forms on the underside of stems and leaves. Oak Apple Wasps, Amphibolips confluenta, only lay their eggs in oaks and favor trees familiar to Virginians; black oaks, scarlet oaks and red oaks. The larvae live inside the gall for a year before they pupate (rest) and emerge from the gall as adults in June and July. An empty oak apple gall will have a distinct hole that was drilled by escaping adults.
As one might expect, enterprising Europeans found a use for oak galls as early as the fifth century. By adding iron sulfate to tannic acid extracted from galls, they were able to produce an ink that was the most commonly used kind in writing and drawing until the early 1900s. Early African and Asian cultures thought galls had medicinal properties as well.
One of the more curious phenomena associated with galls is the formation of “jumping oak galls”. They are little, round galls about the size of a BB. They fall to the ground and jump around as the wasp moves around inside – like a Mexican jumping bean. They occur in large numbers and can make the earth look like it is vibrating!
Most oak apple galls are about one-half inch to two inches in diameter, but some can get larger. Note the drilled hole made by the exiting wasp. Credit: Lorne Field
Check out this video below about jumping oak galls.
The best place to find galls is in a mature wooded area with a lot of oaks. Lewis G. Larus Park on Huguenot Road boasts 106 acres of woods and trails which provide gall viewers plenty of opportunity to snap photos. Rockwood Park in Chesterfield and Bryan Park in Richmond are good gall grounds too.
Remember; take only pictures – galls and the insects they contain are an important part of the ecosystem. They are a food source for animals such as opossums, raccoons and birds.
Please share your gall photos! email@example.com