They are known for their extremely painful stings, (the sting of the species Dasymutilla klugii rated a 3 on the Schmidt pain index and lasts up to 30 minutes[1]), and has resulted in the common name "cow killer" or "cow ant" being applied to the species Dasymutilla occidentalis.

[5] North American Mutillidae have eight phenotypically distinct and geographically limited Müllerian mimicry rings (Desert, Eastern, Madrean, Texan, Red-headed Timulla, Black-headed Timulla, Tropical, and Western) making up one of the largest Müllerian mimicry complexes on the planet.

[6] These mimicry rings are the result of repeated convergent evolution of aposematic traits between co-occurring velvet ant species, rather than shared phylogenetic history.

[7] Through the evolution of aposematic traits in velvet ant species in the same ring, local predators have learned to avoid these well-defended wasps.

The exoskeleton of all velvet ants is unusually tough (to the point that some entomologists have reported difficulty piercing them with steel pins when attempting to mount them for display in cabinets).

Members of the family Myrmosidae, formerly classified as a subfamily of mutillids, also have a distinct pronotum in females, but lack felt lines in both sexes.

Guido Nonveiller (1963) hypothesized the Mutillidae are generally stenothermic and thermophilic; they may not avoid light, but rather are active during temperatures that usually occur only after sunset.

Predation is one of the strongest forces natural selection uses to drive the evolution of an organism's morphology, physiology, and behavior.

Velvet ants avoid predation using the following defense mechanisms: a venomous sting (if female), aposematic coloration, a stridulatory organ in their abdomen, an alarm secretion from their mandibular gland, and a durable exoskeleton.

[12] The venom that velvet ants inject through their stinger has been investigated for five species of Dasymutilla, revealing that they are composed primarily of peptides.

[12] The aposematic coloration of velvet ants often corresponds to a specific Müllerian mimicry ring consisting of dozens of species.

[12] These experiments provide evidence that the aposematic coloration of velvet ants causes their predators to hesitate, acting as a visual defense mechanism.

The stridulatory organ that velvet ants possess produces an audible squeaking when the abdomen is contracted.