Buckeye Yard and Garden onLine

Several BYGLers reported receiving questions about black ants building mounds in landscape beds, along roadsides and in fields. Are they carpenter ants? The black ant responsible for the mounds are not carpenter ants nor are they Allegheny mound ants, they are BLACK FIELD ANTS (Formica spp.). Carpenter ants (Camponotus pennsylvanicus) do not build nests in the soil. They construct their colonies in tree trunks and structures made of wood. Allegheny mound ants (Formica exsectoides) are soil dwelling ants and also construct soil mounds, but are more destructive than black field ants. Although the black field ant can damage some landscape plants by burying them in the mound, most of the time very little damage is done to the surrounding plants. Allegheny mound ants will kill and clear vegetation from around their mounds. They kill the vegetation by injecting formic acid into plants and vegetation near the mound. Small trees and shrubs within 40-50" of large mounds can be killed.

Besides where they live, black field ants can be distinguished from carpenter ants by the shape of their thorax. One needs a magnifying glass or dissecting scope to see this characteristic. Looking at the ant's thorax on profile, the black carpenter ant's thorax is smoothly rounded from front to back. The black field ant's thorax has humps or an uneven profile from front to back. The carpenter ants tend to be larger than the field ant as well.

If control is necessary, the Allegheny mound ant and the black field ant can be controlled by direct application of a residual insecticide to the mound.