Despite their popular name, velvet ants are not true ants but belong to a family of parasitic wasps called Mutillidae. The males of most species are winged (like a typical wasp), but the females are always wingless and very ant-like in appearance, with much of the body covered in dense velvety hairs. It is the females which are most often noticed scurrying about in the open, especially in sandy places, and give rise to the common name of the group.

Female velvet ants are equipped with a very efficient and powerful stinging apparatus. The sting is curved and sometimes nearly as long as the abdomen, and with it they can inject a very potent poison. Hence, some of the popular local names for these insects, such as 'cow-killer'. The sting is not fatal to larger animals, but it can be quite severe and painful. Only the wingless females can sting - the winged males are quite harmless.