[4] Ants belonging to the Formica genus possess a single knob or bump located between their thorax and abdomen.

However, sunlight is important to most Formica species, and colonies rarely survive for any considerable period in deeply shaded, dense woodland.

In North America, at least, these habitats had a long history of frequent landscape-scale fires that kept them open before European settlement.

Conversion to agriculture and fire suppression have reduced the abundance of most American Formica species, while the cessation of traditional haycutting seems to have had the same effect in Europe.

However, at least a few Formica species may be found in a wide range of habitats from cities to seasides to grasslands to swamps to forests of the temperate Northern Hemisphere.

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.

Due to their relatively large size and diurnal activity, they are among the more commonly seen ants in northern North America.

[citation needed] 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.