An erratic aerial approach enables mating survival in the cannibalistic killer fly

Mating encounters often have fatal consequences in cannibalistic species. In terrestrial ambush predators, such as mantids and jumping spiders, the associated fitness-maximizing precopulatory behaviors have been studied intensely.¹ In comparison, we have limited insight into the mating behavioral strategies of sexually cannibalistic and fast-moving aerial predators. Here, we report the approach behavior of the male killer fly, Coenosia attenuata, a highly predacious, cannibalistic species of Muscidae. We show that males of this species employ an erratic approach trajectory to search for, approach, and contact potential mates and that they possibly utilize wing interference patterns to identify potential females at close range. Male killer flies were observed producing erratic flight trajectories over stationary females, generally drawing closer to the female, and exhibiting unpredictable heading angle changes that increased in frequency. The fast turns safeguarded the male from being cannibalized once the female engaged in flight and provided a contact geometry that resulted in mating. The rates of this behavior were significantly higher in satiated males exposed to stimuli with intact wings. In addition, analysis of wing interference reflectance demonstrated significant sexual dimorphism in this species, with female wings reflecting significantly more UV, purple, and blue light (300-700 nm) than male wings. Together, our results show that the reported behavior reduces the risk of cannibalism while enabling the male to contact and mate with the female. This study illustrates how extreme sexual conflict can drive the evolution of complex behaviors in aerial animals. VIDEO ABSTRACT.