Collections of mammalophilic Simuliidae on variously colored and shaped two-dimensional silhouettes indicated that the species oriented to and landed on certain 'preferred' colors. The Prosimulium mixtum/fuscum complex and Cnephia (Stegopterna) mutata were consistently attracted to black targets, the Simulium venustum complex was consistently more attracted to blue silhouettes, and Simulium vittatum oriented and landed on all colored silhouettes except yellow. Black, blue, and red were the most attractive for all species. Colors reflecting the least amount of incident light were the most attractive, a matte surface was more attractive than a glossy one. The response of the flies to simple geometric shapes indicated that all shapes were equally attractive, with the flies aggregating at the points of convergence of the silhouette outline.