Mutillidae are wasps with extreme sexual dimorphism. Males have wings and resemble other wasps; females are wingless, heavily armoured, and covered in dense red or orange hair, so they are frequently identified as ants. The sexes look so unlike each other that some species were described twice under different names before pairs were observed mating.
Defence is layered. The cuticle of a female is exceptionally tough, resisting crushing to a degree unusual among insects. She squeaks by stridulating when handled, and she has a very long sting relative to body size. The Schmidt sting pain index rates Dasymutilla stings high, and the folk name cow killer reflects that; no verified case exists of a cow being killed.
Females are parasitoids. They enter the nests of ground-nesting bees and wasps, including bumblebees in some species, and lay eggs on the host pupae, which their larvae consume. Many Dasymutilla species share nearly identical warning colouration, forming one of the largest known Müllerian mimicry rings among insects.