Gall in stem of Goldenrod, Solidago species. The gall is about 2 cm in diameter. As far as I can tell from references (see guide), this form of gall is specific to the one species of fly. This gall was found in an extensive (acres) patch of goldenrod in a power line right-of-way. There were many "colonies" of 20 or more galls in groups of adjacent stems, but the "colonies" were widely scattered. I collected many galls and hope to see the adult flies in April. I'll photograph the larvae in some galls as well.