One of the most prominent galls in Indiana is made by the goldenrod gall fly, Eurosta solidaginis. At this time of year, unplowed fields will have brown stubble, the new green growth is not yet emerged. The tall stocks of goldenrod can be found in many fields. Some of these stalks will have a round gall, made by the Goldenrod gall fly. The gall is formed by the fly larva which alters the plant morphology and physiology to produce a protected feeding site. Before pupation, the larva will create an exit tunnel. The adults will hatch with the warm spring temperatures.
At this time of year, galls can be collected from the fields and brought indoors to allow the flies to emerge. They are beautiful picture-wing terphritid flies. Flies do not emerge from all the galls. Many of the galls will be parasitized or harbor predators. The beetle predators or wasp parasitoids will emerge from galls that have been attacked.