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The worker ants in this mound between two fir trees have chewed on the bark and injected sufficient formic acid to kill them.

Allegheny Mound Ant

Species: Formica exsectoides Forel


Nova Scotia to Georgia from the Atlantic coast to the western side of the Appalachian Mountains.

Hosts: Soil dweller, attacks any plant or tree near the nest.


This ant attempts to kill any vegetation which may grow on the mound or shade the area. The ants do this by biting the plant and depositing formic acid into the wound. This readily kills small plants but trees may require numerous "stings" over the entire trunk before death results. Attacked plants will be near mounds and the bark will be covered with resin filled blisters.

Description And Life Cycle:

The Allegheny mound ant, as its name implies, builds above ground nests in undisturbed, open areas. The above ground portion, the mound, acts as a solar collector for incubating ant eggs and larvae. This colonial insect has many queens to lay eggs as opposed to other ants which may have only one. A 19-inch high mound may contain 250,000 individuals. The ants feed on other insects for protein and aphid honeydew for sugar. The ants may be red-orange, black or both colors.

Colonies are started by a single mated queen. New colonies take several years to develop enough to make an above ground nest. Larger colonies may also subdivide, like honeybees, resulting in many mounds being located in a given area.

Control Hints:

Large, numerous mounds are difficult to control. This ant will move to a new spot if severely disturbed and new colonies will become established from surrounding forests.

Option 1: Cultural Control - Eliminate Food - Since this ant relies on other insects for food, control of aphids, scales and needle feeding insects will reduce mound ant activity.

Option 2: Cultural Control - Disturb Mounds - Physical destruction of the mounds will usually just irritate the ants and they will reconstruct the mound. However, continual disturbance, such as plowing two to three times a year, will usually cause a colony to relocate elsewhere.

Option 3: Chemical Control - Mound Treatments - General sprays to the mounds are usually not effective. Dusts must be applied to the mounds and around the parameter, at least one foot out, so that the ants will track through the insecticide. Colonies may burrow underground and establish a new colony outside the pesticide application zone. Reapplications of the poisons may be necessary.

Option 4: Chemical Control - Mound Injections - Some fumigant insecticides are available for ant control. However, treatments are costly and only licensed applicators may use the poison.