The pavement ant, Tetramorium caespitum, is a common household pest. It is dark brown to blackish, and 2.5–4 mm long. The name comes from the fact that these ants usually make their homes in pavement. They are distinguished by one spine on the back, two nodes on the petiole, and grooves on the head and thorax.
During early spring, colonies attempt to conquer new areas and often attack nearby enemy colonies. These result in huge sidewalk battles, sometimes leaving thousands of ants dead. Because of their aggressive nature, they often invade and colonize seemingly impenetrable areas. In summer time the ants dig out the sand in between the pavements to vent the nests.
The species does not pose a public health risk, but can contaminate food and should be avoided.