Mound-building, forest-dwelling Formica spp.
such as F. rufa often have a considerable effect on their environments.
 They maintain large populations of aphids on the secretions of which they feed, and which the ants defend from other predators.
 They also prey on other insects.
 In fact, in many countries, they  are introduced in forests to control tree pests, such as swains jack pine sawfly and eastern tent caterpillars in North America.
The effects of mound-building grassland species such as F. montana are not well-studied, but their local abundance, conspicuous mound-building, and very frequent association with aphids and membracids point to a comparably important ecological role.

Formica nests are of many different types from simple shaft-and-chamber excavations in soil with a small crater or turret of soil above to large mounds, under stones or logs, or in stumps.
 None is arboreal.
The genus is abundant in both the Nearctic and Palearctic regions.
 Due to their relatively large size and diurnal activity, they are among the more commonly seen ants in northern North America.
 Some species, including F. rufa, which is common in Southern England, make large, visible thatch nests of dry plant stems, leaves, or conifer needles, usually based around a rotting stump.

Most Formica species are polygynous (have multiple queens per colony), and some are polydomous (have multiple nests belonging to the same colony).
Queens may be singly or multiply mated, and may or may not be related.
 Formica polyctena has polygynous colonies.

Wood ants typically secrete formic acid; F. rufa can squirt the acid from its acidopore several feet if alarmed, a habit which may have given rise to the archaic term for ant, "pismire", and by analogy its American equivalent "piss-ant".
They can be relatively large; F. rufa workers can reach a maximum length  around 10 mm.
The eastern US species F. dolosa and the western F. ravida (syn.
F. haemorrhoidalis) may be slightly longer.
Mound-building, forest-dwelling Formica spp. such as F. rufa often have a considerable effect on their environments.  They maintain large populations of aphids on the secretions of which they feed, and which the ants defend from other predators.  They also prey on other insects.  In fact, in many countries, they  are introduced in forests to control tree pests, such as swains jack pine sawfly and eastern tent caterpillars in North America. The effects of mound-building grassland species such as F. montana are not well-studied, but their local abundance, conspicuous mound-building, and very frequent association with aphids and membracids point to a comparably important ecological role.
Formica nests are of many different types from simple shaft-and-chamber excavations in soil with a small crater or turret of soil above to large mounds, under stones or logs, or in stumps.  None is arboreal. The genus is abundant in both the Nearctic and Palearctic regions.  Due to their relatively large size and diurnal activity, they are among the more commonly seen ants in northern North America.  Some species, including F. rufa, which is common in Southern England, make large, visible thatch nests of dry plant stems, leaves, or conifer needles, usually based around a rotting stump.
Most Formica species are polygynous (have multiple queens per colony), and some are polydomous (have multiple nests belonging to the same colony). Queens may be singly or multiply mated, and may or may not be related.  Formica polyctena has polygynous colonies.
Wood ants typically secrete formic acid; F. rufa can squirt the acid from its acidopore several feet if alarmed, a habit which may have given rise to the archaic term for ant, "pismire", and by analogy its American equivalent "piss-ant". They can be relatively large; F. rufa workers can reach a maximum length  around 10 mm. The eastern US species F. dolosa and the western F. ravida (syn. F. haemorrhoidalis) may be slightly longer.
Formica