Of all the black ants, only five varieties are usually found in homes: pavement, odorous house, acrobat, crazy and little black ants. Spraying is usually not recommended to treat ants because it only kills foraging workers. Even if almost all the foraging workers are killed, the colony is able to rebuild. It is better to treat the entire nest either through the use of insecticidal dust or ant baits.
Tetramorium caespitum grows to about 1/8 inch long and has narrow, parallel furrows on its head and thorax. The name comes from the ant's preferred nesting sites under pavement and slabs, but they are also found under stones and in walls. They typically feed on grease, sweets, insects and seeds. Baiting is usually effective for pavement ants.
Odorous House Ants
Tapinoma sessile has a feature that makes it easy to identify. This 1/8-inch-long black ant gives off a unique odor when crushed, similar to licorice or rotten coconuts. Odorous house ants eat insects and honeydew produced by aphids, and are attracted by sweet baits. They nest outdoors in dark, moist areas such as under stones, logs or patios. They are known for frequently moving nest sites, usually about once a month, and often move indoors after heavy rains.
Crematogaster sp. likes to live in rotten wood and under stones, but may nest indoors in insulation board, roofing or in other damp wood. The ants are easily identified by a heart shaped abdomen, which the ants lift over their bodies -- hence the name acrobat. The ants feed primarily on honeydew. If the ants are nesting indoors, the nest is to be treated with an insecticidal dust in order to control populations. Otherwise, treat them using bait for sweet ants.
Paratrechina longicornis has long legs and antennae, and is known for moving very fast. The ants are very small, only 1/16 to 1/8 inch long. The ants almost always nest outdoors, but forage for food and water in homes, and sometimes nest in potted plants. Crazy ants are a relatively new introduction to the United States, so exact management techniques have not been developed toward them. The ants are omnivores, but almost impossible to attract to ant baits. It helps if sweet bait is used and it is kept fresh.
Little Black Ants
The name little black ant seems like a generic description, but it's not. Monomorium minimum is shiny black and about the same size (1/16 inch) as the crazy ant, but smaller moving. Little black ants like to feed on insects and honeydew, as well as sweets, meats, bread, grease, fruits and oils. The ants nest in the soil or in rotten wood, and are found in the woodwork or masonry of houses. They are treated using either sugar or grease baits.
How to Treat for Ants
There are two effective treatments for killing ants found inside your home: insecticidal dust or poisoned bait. When using an insecticidal dust like boric acid or silica gels, apply in a thin even layer in the ant nest area. If the nest is outdoors, use products approved for outdoor use and follow the directions. Ant baits are usually formulated to attract grease-feeding ants or sugar-feeding ants, so finding one that attracts the type of ants you have is essential for use. Place the bait in areas where ant activity has been seen, but keep it away from pets and children. Baiting takes three to four weeks before it is effective.