Mound Ant

What kind of ant is this
April 26, 2010
These ants are all over the place here in northern Idaho. They live in 1 to 3 foot tall mounds of loose debris. I want to know the name of this ant, please.
beau bugs
north Idaho U.S.A.

Dear beau bugs,
Interestingly, when we began our research on BugGuide, the first thing we discovered is that there isn’t any data of Ants from Idaho submitted to the website to date.  We are relatively certain your ant is in the genus Formica, and the likeliest candidate is Formica obscuripes which is reported from nearby Montana and Washington.  BugGuide has a nice photo of the mound, and nice photos of ants, but next to no information on the species, until we located a single comment on a posted photo.  Wikipedia provided common names for the genus like Mound Ant, Field Ant and Wood Ant, as well as additional information:  “Formica are notable for their parasitic and slave making behaviors. There are three categories.  In the exsecta and rufa-microgyna groups, virgin queens cannot start colonies on their own, but invade colonies of other groups and by various processes eventually oust the host queen and have the host workers help them raise their own brood. Eventually the colony consists of only the invading queen’s offspring. This is called temporary social parasitism.  In the sanguinea group, colonies are started as above, but then in some species of the group workers go out and raid colonies of other groups for new workers to act as a work force, so-called slaves (but this is a poor analogy). Some species of this group need to do this to survive, for others it is optional.  The pallidefulva, neogagates, and fusca groups are those most often parasitized by the above groups. They are also enslaved by ants of the genus Polyergus. The evolution of this behavior is believed ultimately to have been derived from the common habit of many Formica species of adopting recently mated queens into established colonies. Indeed, in many of the parasitic species outside the ‘slave-makers’, this ‘secondary polygyny’ is common.“ According to BugGuide, Formica obscuripes is in the rufa group, and BugGuide recognizes the microgyna group as distinct, having this to report:  “Species of this group are believed to be temporary social parasites of other species of Formica. The female in some way is adopted by workers of the host species. Host workers may remain in the colony after the intruding queen has established her own brood, but the host workers eventually die. Most species are found in open woods or meadows. The nests are usually of the thatch type, but the thatching is normally scattered about the nest openings and appears as a flattened disc.”