These are probably pavement ants, Tetramorium caespitum,althought the image resolution does not allow me to positively identify it. Pavement ants have a sting, but are not aggressive and it uncommon for someone to report a stinging event.  This eXtension video, http://www.extension.org/pages/64889/pavement-ants-in-and-around-schools#.U1rPwledFjs,  describes solutions to pavement ants in schools and may be helpful should the ants decide to invade your home.  Please contact your local Extension agent to confirm identification and to suggest products labeled for pavement ant management in your state.  A granular ant bait applied when these ants are actively foraging may be sufficient to reduce activity near the sidewalk.  To find your local Extension agent, simply go to http://www.extension.org, drop in your zip code and choose the office that is most convenient for you.