Black ants can have two very different habitats. When they are outdoors, they live in a location that is comfortable and close to a food supply. When they have to move indoors, they try to find a location that is similar to the one they had outdoors. When they move indoors, black ants become pests.
Since there are several types of black ants that invade houses, it is important to identify them correctly before trying to control them. The black ants that invade homes might be carpenter ants, odorous house ants, acrobat ants, or little black ants. They have different habitats and the control measures are different.
Black carpenter ants are very large ants. The workers can be ¼” long. Outdoors they usually live in trees, logs, or stumps. They hollow out wood to make their nests. If they can find decayed wood, they will choose it over dry, sound wood. They are active at night and on cloudy days. Indoors, they often nest where there is a moisture problem and wood has gotten wet. Carpenter ants nest in eaves, wall voids, bath traps, and even inside of hollow doors.
Acrobat ants are medium-sized black ants. Workers are about 1/8″ long. When they are viewed from above, the workers have heart-shaped abdomens. When they are disturbed, they hold their abdomen above their body while they run around.
Outdoors, acrobat ants nest under rocks and woodpiles. They also nest in decayed parts of trees. They trail along tree limbs onto the roofs of houses. They often hollow out Styrofoam sheathing and insulation to make tunnels and nests. If they find abandoned termite damage, acrobat ants will clean out the galleries to make a nest. Homeowners often find piles of debris before they see any acrobat ants.
Little black ants are common home invaders. Scientists call these tiny ants Monomorium minimum. Outdoors, these ants live in nests in the ground. The workers often forage into houses for food. They march in lines across the foundation or over a windowsill. If the colony moves indoors, the ants make their nest behind a baseboard or under the base of a cabinet.
Because their habitats are different, it is helpful to identify the type of black ant that is becoming a problem before starting to control them. A thorough inspection is usually the first step.