Identifying which type of ant is causing you problems is important when trying to select the right control methods. While there are literally thousands of different types of ants, only a few venture inside our homes. Keep in mind that many ant species look very similar and getting an exact identification may require consulting an expert.
Pharaoh ants are one of the few ant species that frequently nests inside homes and buildings. They are light yellow or red with a darker coloured thorax (chest) and about 1/16 inch long. They are often confused with thief ants, but you can recognise pharaoh ants by their normal-sized compound eyes in proportion to their heads and twelve-segmented antennae with their three-segmented antennal clubs. Nesting sites are often in dark, warm places near a moisture source. They do not have a mating swarm but produce new colonies by budding, which means a group of ants will leave an overly large colony to form a new one.
Large black ants found inside homes are usually carpenter ants. They can also be red and black and are about 3/16 to 1/2 inch long. Despite their name, they do not eat wood, but they do chew on it to make tunnels. You will usually find their nests in moist or rotten wood either inside or outside your home. They like sweet foods, such as honeydew, syrup, honey, jelly and sugar.
Odorous House Ant
Odorous house ants are so named because they give off an unpleasant smell when crushed, similar to rotten coconuts. They are brown and about 1/10 inch long. They like sweet foods, especially honeydew, and insects. Nesting sites can be found under stones, boards, mulching plastic or any object lying on the ground. In homes, nests can be found in wall voids or under floors.
Pavement ants are about 1/8 inch long and reddish brown to black. Their name comes from the tendency to nest under sidewalks, cement slabs and driveways, but they may also build nests under stones, logs and other concealed sites. They will eat almost anything, but prefer meats, pet food, sweets and insects.
Thief ants are yellow to light brown in colour and about 1/20 inch long. They are also known as grease ants because they like proteins and greasy foods, such as meats, cheese and peanut butter. Thief ants can be confused with pharaoh ants. Thief ants have smaller eyes and a ten-segmented antennae with a two-segmented antennal club. They build nests in soil or rotted wood, but can be found nesting inside in small places that are often difficult to find.
Cornfield ants are light to dark brown and about 1/10 inch long. They make their nests in the soil and enter homes only in search of sweets. They also feed on honeydew and insects. They look very similar to odorous house ants, but their first antennal segment is about the same size as their head, while odorous house ants' first segment is much longer. They also have very large eyes.
Large Yellow Ants
Large yellow ants are about 3/16 inch long and yellowish or reddish brown. They are also called citronella ants because they produce a lemony smell when crushed. Nesting sites are usually found under stones, logs, brick, concrete or similar structures. Workers rarely enter indoors, but they can cause "termite scares" when they push soil out of basement cracks, according to Karen M. Vail, an associate professor of entomology and plant pathology with the University of Tennessee. They typically feed on honeydew.
Imported fire ants are so named because their venom produces a burning sensation when injected. They are quick to attack when their nests are disturbed and will often run up any vertical surface. They are about 1/8 to 1/4 inch long and dark brown. They usually build their nests outdoors, but can occasionally be found indoors in utility structures or tree trunks.
- University of Minnesota Ext; What to Do About Household Ants; Jeffrey Hahn and Phillip Pellitteri
- University of Tennessee Agricultural Management Service; Managing Structure-Invading Ants; Karen Vail
- University of Nebraska-Lincoln Extension: Ant Identification
- Colorado State University; Ants in the Home; W.S. Cranshaw; January 2009
- University of California IPM Online; Pests of Homes, Structures, People, and Pets; February 2007