Two species of large carpenter bees (genus Xylocopa) were studied in southern Arizona. Nesting preference of X. c. arizonensis in floral scapes of Agave palmeri was found to depend on floral scape age and status of the thermal microenvironment. Evidence suggests that females assess scape age with extreme accuracy and this ability enables them to avoid those scapes that are degraded by other biota. Females also preferentially used Agave scapes that were shaded from the afternoon sunlight. Male mating behavior and lek site selection of X. varipuncta was also investigated near a large nesting site in a topographically flat area. Behaviors analyzed indicate that males tend to display singly and that they disperse pheromonal signals. Lek site selection was in accord with that found at three other study sites and further demonstrated that males did not clump their territories near nest sites. Distribution of male territories therefore does not appear to correspond to female distributions in the environment.