Back in September I took a photo of a goldenrod gall. The gall was formed in response to a goldenrod gall fly having laid eggs on the stem of the goldenrod plant. The eggs hatched in about a week and a half, and at least one of the larvae burrowed into the plant’s stem. It’s saliva apparently stimulating the plant into growing the gall around itself.
It’s now January and the larva is still inside the gall.
The gall helps protect the larva from predators and supplies it with food until it’s ready to pupate. In spring, an adult fly emerges from the gall.
The galls caused by these insects don’t do significant damage to the plant. As you can see in the comparative photo of the same goldenrod plant above there is as much leaf growth above the gall as there is below it. And, though you can’t see it in the photos, the plant produced both flowers and seeds.
The adult goldenrod gall fly (Eurosta solidaginis) is a small brown fly with brown splotched wings.
The fly’s specific name solidaginis refers to the goldenrod plant’s genus name, Solidago.