I cut open the fuzzy bud of a rose and found these critters. I found information on a Minnesota extension website and editted to refer to the mossy rose gall. Galls are abnormal plant growths resulting from activity of the tiny, non-stinging cynipid wasps. The mossy rose gall looks like a mossy sphere and are caused by Diplolepis rosea;. Insect larvae develop inside the gall. Numerous galls may stress the plant because nutrients otherwise available for plant growth are used to produce galls.
Control is best done by pruning out galls before the wasps have matured and emerged from the gall. Since adults emerge from the old galls in spring, prune out the galls after the leaves drop in fall, cutting below the gall and above a bud. Removing the galls from the garden may not totally eliminate future problems if adult wasps fly in from nearby areas. Timing for insecticidal treatment of these wasps is difficult and not suggested.