Wild Georgia: Unusual growths on leaves, trees can hold a secret world

When you’re outdoors at this time of year, you might encounter a lot of gall — or I should say galls, which are abnormal growths on leaves, stems and twigs of various plants. In a way, galls are similar to warts or benign tumors in people.

Galls may appear in many forms — as swollen bulges on goldenrod stems, slightly raised red spots on maple leaves or what seem to be small apples on oak trees. In general, the unusual growths are induced by a wide variety of tiny wasps, flies, midges, mites and aphids to protect and nourish their larvae — tiny nurseries, if you will.

It’s why many people, including me, find galls fascinating. Hundreds of different types of plant galls occur in Georgia. A single white oak tree may harbor dozens of types. Rarely, however, do the galls cause major harm to the host plant.

One gall enthusiast is my friend Bill Sheehan, a retired entomologist in Athens. He has an amazing photo collection of gall types that he has found in Clarke County. See his photos at inaturalist.org/projects/galls-of-clarke-county-ga-usa?tab=observations.

Some of Georgia’s most common gall types are “oak apple” galls and goldenrod galls. The gall-forming process used by the goldenrod gall fly is typical of that of many other gall-causing insects.

If you cut open a goldenrod gall in fall, you’re likely to find on the inside the larvae and pupae of the gall fly. The female laid her eggs on the stem in spring. A larva from a hatched egg chewed its way into the stem, causing a golf ball-size gall to start forming and harden around the larva. No one knows just how a larva causes a gall to start, but it may have something to do with the larva’s saliva, which may mimic plant hormones.

The larva will stay in its gall the rest of the year and continue to develop. By late fall, it will be plump and ready to enter the pupal stage to develop into an adult, which will emerge next spring.

But the larva is not always safe — downy woodpeckers in winter often peck into the galls and retrieve the fat, tasty larva.

IN THE SKY: From David Dundee, Tellus Science Museum astronomer: The moon will be first quarter on Friday (Aug. 5). Rising in the east are Mercury (very low) just before dawn; Venus, a few hours before sunrise; Mars, around 2 a.m.; Jupiter, around midnight; and Saturn, a few hours after dark.

Charles Seabrook can be reached at charles.seabrook@yahoo.com.