After mating, females will scurry about looking for wasp or bee pupal chambers. Once found, they will enter a nest and use their ovipositor to lay an egg on or near to the host. If the parent is still present, the velvet ant may be carried away by the other bee or wasp. A grub-like larva will emerge from the egg, feed on its host, and grow to full size in a matter days. The shell of the original inhabitant then becomes a site to construct a cocoon for the velvet ant pupa.
Some adults emerge that summer while others overwinter in a pupal or prepupal state.
When harassed, and during mating, velvet ants produce an audible squeak. Velvet ants are also known as cow killers or mule killers because of their extremely painful sting. Like all wasps, they can sting multiple times. Because of their armor-like exoskeleton and painful sting, few if any animals consume this conspicuous wasp.