Synonyms and other taxonomic changes
Several barely distinguishable varieties and subspecies of this ant have been described, all now considered minor, either local or regional color variants, and thus synonyms of F. exsectoides proper.
Explanation of Names
resembling F. exsecta, a related Eurasian species.
workers 4.5-7.5 mm, sexuals 8-9 mm.
The head shape of workers and queens, with its distinctly concave rear margin (vertex of the prognathous head), is characteristic. Red head and mesosoma with black metasoma are common in this genus, but combined with with this head shape, and somewhat shiny surface, is diagnostic.
The nest architecture is distinctive -- large (often >1m.), rounded, subconical, primarily earthen mounds. Other Formica mounds either contain more stems, conifer needles, petioles, leaflets, etc., or are less evenly domose in shape.
This ant has a somewhat inappropriate English name, as it exists well beyond the Allegheny drainage. F. exsectoides occurs sporadically, in appropriate habitat (what little is left of it) from Nova Scotia south to the mountains of Georgia, west across Canada and glaciated central USA to the eastern face of the Rocky Mountains, south to northern New Mexico.
F. exsectoides inhabits oak or pine savannas and open oak woodlands or pinelands, sunny openings in denser tree populations, the edge of prairie groves, and open meadows and mesic tallgrass prairies.
Everywhere, it builds large, subconical, mainly earth mounds. These catch the sun’s rays and warm early in spring, and are warm to the touch on sunny days, even when barely above freezing.
This ant apparently subsists largely on honeydew and extrafloral nectar, but also scavenges or occasionally preys on various arthropods, especially phytophagous insects. One can watch a nest for some time, observing numerous incoming workers returning swollen with liquid food, and few to none carrying in prey items.
New colonies may be founded by "temporary social parasitism", in which a mated queen invades a congeneric host species (F. subaenescens, F. subsericea reported, but others more likely in some localities). Mature colonies have multiple queens and apparently undergo fission, resulting in characteristic clusters of intercommunicating, large mounds.
Hedlund's online catalog of ants of North America
contains a good summary from the literature on this ant.