[1] F. obscuripes creates distinct, dome-shaped mounds composed of varying materials found in the nest's surrounding environment.

The mounds are typically constructed in areas devoid of cover to expose the nest to sunlight.

Formic acid is then sprayed into the open layer eventually killing and felling the plants.

A supercolony in a four-hectare (9.9 acre) study area near Lehman Hot Springs consisted of 210 active nests with an estimated population in excess of 56 million ants.

Pacific Northwest populations are additionally distinguished by the unique coloration of the gynes, which sport entirely black bodies with red heads.