This photo was taken in 2007 but the ants were only identified today at bugguide.net. The identifier said that this is "a common eastern North American species, here recognizable by its slightly silky sheen (as the specific epithet suggests) and rounded rear margin of the head." In the references I read on the web, these ants are also slave holders. I only just learned about slave ants this past summer from Summer World: A Season of Bounty. Summer is coming. I urge you to click the link and buy the book in preparation for this coming summer. It is a valuable guide to the forests and meadows of New England.
I found an ant blog today at http://www.antweb.org/antblog. Go check it out and see if you want to subscribe to the RSS feed like I did.