The aphid Schlechtendalia chinensis (Bell) induces galls on its primary host, Rhus chinensis Mill. We studied temporal changes in gall and aphid clonal population size throughout the period of gall development. Gall-size changes occurred in four stages: a first slow growth period, a fast growth period, a second slow growth period, and a growth reduction period. Gall volume and surface area increased abruptly toward the end of July, peaking during October, in parallel with an increase in aphid clonal population size, from one individual to >10,000 aphids per gall. Clear changes were seen in the clone dynamics of S. chinensis. Fundatrix began to produce first-generation apterous fundatrigenia during late May to early June. Second-generation apterous fundatrigenia appeared at the start of July. Alate fundatrigeniae with wing pads first appeared at the end of August, but accounted for <1% of the individuals in the galls. Adult alate fundatrigeniae first appeared at the start of October. Abrupt changes in aphid density and crowding might trigger the induction of alate morphs in the galls. Of the eight gall properties that we recorded, gall volume was the most accurate measure of gall fitness.