Goldenrod Gall Fly

We were wondering what this was when we were at the Nature Preserve last week and yesterday when we were at Brukner, I found out. This is the "gall" that houses the larvae of the Goldenrod Gall Fly. The female Gall Fly injects her eggs into the stem of the Goldenrod. The eggs will hatch in about 10 days and will immediately start eating from inside the Goldenrod stem. Their saliva has a chemical in which causes the plant to grow abnormally and create the ball-shaped gall. The larvae will live in the gall for a full year before coming out. First, they will eat from inside the gall making it bigger until it is about the size of a golf ball. Then in the fall, the larvae will dig an escape tunnel but will not use it until spring. During the winter the larvae produces a chemical similar to antifreeze which allows them to survive. Then in the spring the larvae will go into the pupa or resting stage before becoming an adult. They will then come out of the gall and look for a mate. Adult Gall flies do not eat and live for only about two weeks.