Velvet ants are not ants at all but rather solitary female wasps.  These ants parasitize bee and wasp nests.  The females are quite large (up to 1/2 inch) ,wingless, very hairy and colored bright orange or red with black in between. The sting from one of these wasps is one of the most painful of any insect.  Some sting so painfully that they are referred to as "cow killers."  The wingless females (males are winged and rarely seen) can make a squeaking (screaming!) noise when captured. Males of this species are winged and usually larger than the females. 

Correction: March, 2002 - David Shappirio, Professor Emeritus of Biology, University of Michigan, was kind enough to send a note regarding the earlier misidentification of this western species of  Mutillidae. I am grateful for his very kind input.

Dennis Haines was then consulted and advised the species pictured here is Dasymutilla aureola pacifica, not occidentalis. Dennis added that the velvet ant pictured is the most common species found at Kaweah Oaks Preserve. But if you find a light one, then he says, "The hairy blonde species is Dasymutilla sackenii."

Here's more from Dennis:  Most of our Mutillids are nocturnal, the Dasymutilla being the exception.  The males can be collected at black light. The females are rarely seen or collected. In fact we have two genera, one made up almost entirely of females and the other genus only known from males.  It doesn't take a rocket scientist to figure out that they represent one genus, but sadly no one has been able to collect both male and female together, and there are numerous species flying around at the same time. Many of these western nocturnal species were described by Mickel, who never got around to publishing a key or presenting holotypes. So all we have are his descriptions to go by.  Very confusing!