Usually they are seen during the cooler parts of the day. Although usually found in relatively sandy areas, they occasionally may find their way indoors. Velvet ants are not phytophagous. The adult is known to feed on bees and other wasps at times. The larva is an external parasite of various bee and wasp larvae and pupae.
Some species are parasitic on various beetles and flies.
Each chews a hole through the cocoon wall and deposits a single egg on the host larva. Usually the hole is sealed and the next cocoon is attacked. The egg hatches and the velvet ant larva feeds on the host. This host is ultimately killed. Females are capable of inflicting a very severe sting if handled or stepped on with bare feet, hence the common name of cow killer.