Is there a good spot on the web to see a range map and habits of these critters? The nest has to be under the house. It definitely looks like F. sanguinea.

Formica aserva is a fairly common member of the sanguinea species group which you should have in your area, and my experience with them locally is that they're adaptable ants who aren't dependent on the sun the way the Allegheny ants are and who quite often nest under stones and logs or even just tunnel into the sides of banks or slight overhangs with never a mound in sight...so yes, they're one of the better Formica candidates one might find nesting under a porch. All the sanguinea Formicas also tend to have a distinctive 'clypeus notch' you should be able to make out with a decent magnifying glass. To narrow down your ID yourself, try catching about ten different individuals from your colony in a small glass or clear plastic container and examining their faces closely for this trait once they calm down and sit still, and if some of your subjects have it (I find it's about 50/50 whether they do or not), then I'd say you've got some sort of sanguinea group ant in hand.

The following link has some good info about all the Formica ants to be found in North America, including their range maps--click on the 'Formacinae Genera' entry in the column on the left side of the page that pops up, then click on the 'Formica' entry on the next page.

http://cs.unc.edu/~hedlund/ants/

And for a really expert ID, you can always try running your photos past some of the myrmecologists who post over at the antfarm forums!

http://antfarm.yuku.com

Not complete by any means, but you might check here: http://www.antweb.org/