Paper wasps have variable black facial patterns that signal their fighting ability. Wasps with more of these irregular black spots on their faces win more fights and are avoided by rivals. Photo courtesy of Elizabeth Tibbetts.

Two female paper wasps fighting. In laboratory experiments, bouts between rival females were videotaped, and aggression was scored based on the number of mounts, bites, grapples and stings observed. Photo courtesy of Elizabeth Tibbetts.