Polyergus breviceps is a species of ant which is endemic to the United States. It is a social parasite of other ants, namely of Formica gnava but also of Formica occulta and Formica argentea. Polyergus is an inquiline parasite, having lost its ability to take care of its young and themselves. "The workers do not forage for food, feed the young or the queen, or even clean up their own nest".