Despite one common name, there are two species of Pavement Ants to look out for in North America (11 in total but most are restricted to the south west). Tetramorium tsushimae and Tetramorium species E. are the main ones found in the US, though which one you have makes little difference. Both are virtually identical. Don't let the links to antweb in this paragraph fool you; you're looking at a fraction of the total diversity within a colony. I'm not even sure I linked to the correct T. species E. In North America for the past ~180 years both species were simply assumed to be Tetramorium. caespitum. That species is only found in Europe, so what we have in North America has been found, mostly through DNA I think, to be the two species linked above. Now species E. doesn't match up properly with anything but it's generally known that it's not native. So the species name seems to be in limbo until someone figures out what is going on.
In short, though, they're pavement ants. T. species E. is typically .5mm longer than T. tsushimae and more often than not, T. species E. is uniformly black or dark brown. T. tsushimae tends to be smaller, and has a lighter mesosoma (middle body segment). Both traits of which vary within a colony. As I said though it makes little difference.
Early on in the year colonies make a series of foraging tunnels that branch out from the main area they over wintered. I suspect these can be used later on as an escape rout should another colony push on their front door. And at the same time these tunnels allow the colony to reach out into the surrounding land and control an area. (About 15' from the nest?)
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