Loath as I am to do an identification over the www without so much as a dodgy picture, it sounds like it could be pharaohs ants - which is bad news.
Whatever you do, DO NOT attempt to treat them yourself. They have multiple queens, and if the colony is threatened, they 'bud' off to form lots of smaller colonies, making the problem much, much worse.
Call in some professionals, and get a proper ID before you do anything else.