Forda formicaria von Heyden is one of the most common galling aphids on Pistacia palaestina in Israel. We report here on the distribution of the galls on shoots and leaves of the host tree. Using three indices of gall abundance, we illustrate changes in abundance of the characteristic crescent-shaped final galls on individual trees at one site from one year to the next. We describe the pattern of temporal changes in clone size within galls during the summer. Although the galls reach their final size shortly after gall induction, when they contain the single fundatrix nymph only, tissue differentiation in the gall wall continues throughout the summer, apparently due to stimulation by the increasing aphid clone.