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Ants in turf

Jeffrey Hahn, Extension Entomologist

Ants are one of the most common insects we encounter. Many species nest in the soil and can cause problems in lawns and other turf areas. There are two common types of ants that residents may encounter: field ants and cornfield ants.

Field ants are about 1/4 inch long and black or red and black. Their nests are mound-like and can cover a fairly large area in the ground, up to two feet in diameter. Field ant can be found in healthy, vigorously growing turf.
Field ant nest.  Photo: Jeffrey Hahn, UMN Extension

Residents can confuse field ants with carpenter ants. While these two ants are somewhat similar in size and color, carpenter ants do not nest in the soil but prefer to nest in moisture-damaged wood. The mounds created by field ants can also lead some people to believe that they are fire ants. However, fire ants only occur in the southeastern area of the U.S.; the closest fire ants to Minnesota are in southern Tennessee. While field ants can bite, it is not as painful as the stings of fire ants which create a burning,very intense pain

Cornfield ants can also be found in home lawns. They are smaller than field ants, about 1/8th inch long and range in color from light to dark brown. They construct small, conical mounds, particularly in areas where bare or thinning areas of lawns are present.
Cornfield ant nests.  They take advantage of sparse, thinning
grass.  Photo: Jeffrey Hahn, UMN Extension

Fortunately, ants do not injure or kill grass, despite the circumstantial evidence. Even the excavated soil on top of the grass caused by field ant nests does not typically cause any lasting damage to the grass (just rake the soil periodically to prevent it from mounding up). It is possible to dull lawn mower blades when they hit ant mounds. Ant activity may also make the turf look like it is being undermined by the tunneling but this is unlikely - a very large nest would need to be present to cause that kind of damage.

Management of ant nests can be challenging. It is not possible or practical to try to control all of the nests on a property. Tolerate ant nests when possible. Treat particularly troublesome nests with a granular insecticide labeled for ants in turf (follow all label direction carefully). Common active ingredients include bifenthrin, B-cyfluthrin, and permethrin. The products typically need to be watered in after application.
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