Lasius is a genus of formicine ants. The type species for this genus is the black garden ant, Lasius niger. Other major members, which live in drier heathland, are the cornfield ant, L. neoniger, and L. alienus. Other species include the temporary social parasites of the L. mixtus group and the hyper-social parasite L. fuliginosus. Lasius flavus is also a commonly seen species, building grassy hillocks in undisturbed pasture. In the Alps, these mounds – always aligned east to catch the first rays of the rising sun – have been traditionally used by goatherds as natural compasses. Species in the subgenus Acanthomyops, in particular L. interjectus and L. claviger, are commonly known as citronella ants due to their citronella-like smell.
Social parasitism
Several species in this genus are noted to be social parasites. Some species such as Lasius latipes and Lasius murphyi are noted to have their mating flights in mid-late summer and invade other colonies of Lasius, primarily Lasius neoniger. Other species, such as Lasius claviger, are known to overwinter and invade colonies in the spring. They can infest buildings, particularly foundation forms in contact with soil, becoming a minor nuisance.