The Goldenrod Gall Fly, Eurosta solidaginis, a member of the fruit fly family, is responsible for these galls, which do not harm the plant. In late spring, early summer, the fly lays an egg on the stem of the newly growing goldenrod. The plant tissues form a hard ball around the intrusion, that is, the egg, and in time the eggs hatches into a larva which spends the winter in this protective shelter. Only perhaps not so protected as it may seem. Red squirrels, mice, and some birds all seek out the insects inside. Here both galls have been chewed by a squirrel to get at the larvae.