Male behavior and the significance of odor signals in mate-seeking were investigated in the spiral-horned bees Systropha planidens and S. curvicornis. In both species the females are oligolectic on the bindweed Convolvulus. Males held territories containing Convolvulus flowers, suggestive of resource defense polygyny. They patrolled fixed routes over flower patches and defended them against other males. In physical combat, grappling males struck each other repeatedly with the sharp-edged apex of their metasoma employing the conspicuously enlarged eighth sternum as a ram. Head width measurements showed that males in both species are larger than conspecific females. Most copulations occurred in Convolvulus flowers. Behavioral experiments with scented bee dummies revealed evidence for odor-cues in mate recognition. It is probable that long-range visual signals are used to locate competitors and mates on flowers, whereas at close range, chemicals presumably on the cuticle surface are responsible for sex and species recognition.