Males of the little known crabronid wasp Tachysphex menkei Pulawski engage in hilltopping behavior at the peak of Usery Mountain in central Arizona. Males are active at midday in the late spring at this location. Individuals perch on and launch out and back flights from small rocks near prominent plants growing at the highest parts of the undulating ridgeline that makes up the peak. The same set of sites attracted two generations of males (in 2009 and 2010). If site-faithful males are territorial, resident males (those that returned to their perches over at least two days) should be larger on average than the males that replace them after the residents have been removed. This expectation was met. In keeping with the hypothesis that hilltopping is a mating system of last resort, only a few males were seen on any given day and no females were observed, suggesting that the population of the species is small and dispersed, at least in central Arizona.
