Allegany mound ants, Formica exsectoides, build large conspicuous nests in open fields and in open areas in woodlots and forests. Their large mounds are constructed of soil brought up from excavated galleries below the nest. Large colonies may include over 250,000 workers and over a 1,000 egg laying queens. The mound acts as an incubator for mound ant larvae and pupae.
The ants kill nearby vegetation including small trees and shrubs to keep shade off of the mound. They do this by chewing a small hole in the bark and injecting formic acid into the wound.
Not surprisingly, they can be a real pest in nurseries and Christmas tree plantations. They will aggressively defend the mound by biting those who dare to disturbed it. This can make life very unpleasant for those who happen to share their yards with Allegany mound ants. Mature mounds may reach over 30 inches in height, six feet across, and the subterranean galleries may go to a depth of six feet beneath the ground.
Mound ants feed on most any type of small insect or arthropod they find as they forage or hunt over the ground. The ants also collect the honeydew secretions from sap-sucking insects such as aphids and leafhoppers. They rarely enter homes or buildings in search of food, which is a very good thing.