Synonyms and other taxonomic changes
Long suspected to belong very near Lasius, Acanthomyops is confirmed by several studies to be properly placed as a subgenus of Lasius.
The idea that L. alienus. L. flavus & L. umbratus occur in NA dates back to E.O. Wilson's 1955 global revision of this genus. For now, we're stuck with these names, but it seems very likely that a modern revision will resurrect the names americanus, brevicornis & aphidicola, respectively, for the American populations of these three.
Explanation of Names
Lasius means fuzzy or hairy, a characteristic of some of the most common species (but many are shiny).
Common brown to yellow ants with short and somewhat upwardly sloped dorsal propodeal surface in profile, and a notably longer posterior declivitous face; the flexor (ventral) surfaces of the middle and hind tibiae usually lack pilosity, but even when they have erect bristles, do not have the hairs arrayed in two parallel rows.
Temperate Northern Hemisphere
Forests and grasslands, typically in mesic habitats, a few found in fens and bogs
Workers of epigeic species forage throughout the frost-free season, and so apparently do the subterranean species. Queens of some parasitic species fly in fall, and may be found above ground (under logs or out searching for potential host colonies) well into the following spring. Mating flights of others typically occur in July through early October. In the southernmost parts of the range (north-central Florida), natural flights can occur as late as early December, and occurrence of alates in heated buildings may occur in winter much farther north.
Many or all subterranean species have mutualistic relationships with root-feeding aphids, and all species in the genus are fond of honeydew. Epigeic species also gather extrafloral nectar. Aphids mutualists eat some of the young of their bugs, while non-mutualists commonly scavenge protein of dead insects and other carrion.
Just mated Lasius (Lasius) & L. (Cautolasius) queens have large fat stores, and can found colonies independently, after mating in the air, then sealing themselves in a small nest in soil or rotting wood. All or most of the species in other subgenera are parasitic during colony foundation, and must gain entry to a colony of a species of the subgenus Lasius (Lasius), or less often, on L. umbratus to rear their first brood. Nonetheless, it is remarkably difficult to find mixed-species incipient colonies, perhaps because the parasites preferentially invade or are most successful in invading very young host colonies, also difficult to find.
Most species are social parasites on a relatively small number of abundant host species in the typical subgenus, and many are subterranean.
Many are mutualists with root-feeding aphids. Occasionally one may find a large segment of a colony with its dormant aphids and their eggs, and the ants' own first instar larvae, under large rocks in winter.