The purpose of this study was to examine whether the density of sawfly galls on Arroyo willow in the Arroyo Seco, Pasadena, California were affected by physical and biological factors. The sawfly is a small wasp that induces galls on willows, where the sawfly larvae develop. The independent biological factors that I am investigating are the amount of leaf resource, the size of the tree, and the number of shoots. The independent physical factors that I plan to examine were light, nitrogen content, distance from the water, and soil quality. In this poster, I present data only on sawfly density in the study area.