Field Ant

Latin Name

Formica spp.


Depending on the species, the size of the workers ranges from 4 to 8 mm. Coloration includes yellow, red, black or a combination of red and black.

field ant picture

Behavior, Diet & Habits

Field ants encompass a large group of ant species belonging to the genus Formica. These ants make their nests in the ground in lawns, gardens, fields and parks.

Field ants usually nest near trees, rocks, sidewalks, fences or foundations of buildings. Many species of field ants make a mound with the soil that they excavate under the ground. Sometimes people mistake these mounds for fire ant activity. Field ants do not sting, but they will bite when they are disturbed. Some field ants can spray formic acid while they bite, so their bites can be painful.

Some species of field ants, like the western thatching ant, Formica obscuripes (Forel), make mounds of leaves, grass, twigs or even pine needles. Others, like the California red-and-black field ant, Formica occidua (Wheeler) and the brown field ant, Formica cinerea (Mayr), make their nests in cracks of sidewalks or beside trees or foundation walls.

Field ants eat honeydew. This is a sweet substance that they get from insects like mealybugs and aphids. They find the aphids on trees and shrubs. Some species of field ants, like the silky ants, Formica fusca (L.), keep herds of aphids so there is always a supply of honeydew. Field ants also eat other insects. Some field ants are attracted to meats. Many species of field ants are scavengers.


Due to the diversity of the genus, it is difficult to make generalizations about reproduction since it varies somewhat between species. At a basic level the colonies consist of a queen who produces eggs. The eggs become workers who perform the necessary daily tasks of the colony.

Signs of Field Ant Infestation

The activity of workers is an obvious sign. Considering the diversity of these ants, there aren’t many other common signs.  The most likely encountered types of field ants, sometimes called thatch ants, produce distinct mounds made of grass or other plant materials.

More Information

Field ants do not usually invade homes. However, the workers will often hunt for food on decks, porches and patios. Sometimes people see black field ants on a wood deck and assume they are carpenter ants.

Preventing field ant problems begins with a careful inspection. Look for things that the ants might use as nesting sites. Place firewood on racks off of the ground and store it away from the house. Move mulch away from the foundation to discourage ants from nesting. Make sure exterior doors close tightly. Replace weather stripping where it is missing.

It is advisable to contact your local pest control professionals. They will have the products and the equipment to control field ants effectively.