Are ants damaging my black walnut tree?

Asked May 26, 2014, 11:44 AM EDT

I have two black walnut trees in my yard. They are about 12 feet apart. The larger one is about 36 inches in diameter, and the smaller is about 24 inches in diameter. At the base of the larger tree is a large anthill, and the ants are climbing up and down the tree. About two feet up from the base of the tree, there is what appears to be a scratched or rubbed area. Should I be concerned about the ants damaging the tree?

Ramsey County Minnesota

1 Response

Many types of ants live around our homes. Most of the time, they are primarily a nuisance and cause little damage. When considering whether to control ants, the first step is identifying the type of ant to determine where it lives, what it eats, and what management practices are best. For help in identifying the ants in your yard, see the Ant Identification section of the University of Nebraska-Lincoln Extension publication Insects, Spiders, Mice & More or the University of Minnesota Extension website page What to do about household ants.

Ants are to be expected in lawns. Some ants nest in thin areas of the lawn. These are small ants, which make small mounds, approximately 3 inches in diameter. Their preference for nesting in areas of sparse vegetation can lead to the assumption that the ants are causing poor lawn development. This is not true. Ants do not feed on turf and so pose no threat to lawns. Control is not justified on the basis of protecting the lawn.

Field ants nest in areas of lawn that are growing well. These ants can build raised mounds of more than a foot in diameter. These large, high mounds can harm the grass and interfere with the lawn mower.

Carpenter ants do not live in soil. They nest in trees in one of two situations: 1) in rotted, decayed wood or 2) in the center heartwood section of the tree. In either case, they are not harmful to the tree. Control is unnecessary for the tree's health, as the ants are taking advantage of preexisting soft, weak wood to establish their colony. Insects, disease, or environmental conditions such as drought are often responsible for weakening and killing limbs or sections of trees. This process allows wood rot to set in, which results in wood decay, giving carpenter ants the opportunity to colonize the tree. Carpenter ants use knots, cracks, holes, and old insect tunnels to gain access to these areas. Control of carpenter ants in trees is warranted if there are indications that ants are entering homes from colonies in trees. If such evidence exists, the best control method is to bait the colony. For more information, see the University of Minnesota Extension website page Carpenter Ants.