Goldenrod Gall Fly

As we were on a hike yesterday we saw a bunch of galls in a meadow of golden rod. We had no idea what they were but it was hard not to notice them there were so many of them. As we continued on our way we found one on the ground that someone else had broken off. We decided to take this one home and try to learn about galls. Galls are are abnormal outgrowths of plant tissues and can be caused by various parasites, from fungi and bacteria, to insects and mites. The gulls we found turned out to be from the goldenrod gall fly. The goldenrod gall fly's entire life revolves around the golden rod plant. These flies don't actually fly well so they in fact spend most of the two weeks of their adult life walking up and down the goldenrod plant looking for a mate.
After mating the female fly lays her egg in the stem of the golden rod plant. The larvae hatches after about 10 days and starts to eat. The saliva from the larvae has a chemical in it which causes the plant to grow abnormally forming a ball shaped "gall" that the larvae will live in.
The larvae will continue to eat from with in it's gall all summer causing it to grow larger. Sometimes as large as a golfball. As summer turns to fall the goldenrod and gall will turn brown and the larvae will dig an escape tunnel that it won't use until spring. The larvae prepares to spend winter in the gall by producing an antifreeze type chemical which will keep it from freezing during winter.
In the spring each larvae will become a pupa and then eventually an adult when it will leave the gall. Adult goldenrod flies do not eat. The galls do not hurt the goldenrod plant.