Carpenter ants can do structural damage to our homes. The information given here is for those ant species exclusive of carpenter ants though many of the same principles apply to them.
Ants feed upon almost anything that people eat and on many other things as well. Most ant nests are outdoors in the soil and the workers forage into the house. Ants may forage up to 100 feet from their nest.
You may find ants nesting between the floor and subfloor, in the walls, behind baseboards, beneath cracked basement floors, in decayed or rotting house timbers, in insulation, or even in a pile of old newspapers. Ideal ant nest locations are anywhere there is heat and moisture, such as near leaky hot water heaters, bathtubs, and toilets. Some even have satellite colonies that live in the house while the main colony is in the soil.
All ants form colonies with one or more queens that lay eggs, workers that feed the queens and the young, and winged sexual forms that usually swarm once a year to mate and start new colonies. The queens may live from 1 to several years depending upon the species. The workers are the ones we find in our food and homes. Workers live about 10 weeks spending their life feeding and protecting the colony. In the spring or fall the sexual forms swarm. This is when you may find hundreds of flying ants in your house. The odorous house ant is the most common ant in homes, with the pavement ant the next most common. Other ants found in houses are the lasius ants, little black ants, and thatch ants.
FINDING THE NEST
We are fortunate that our most common ant species nest in the soil, frequently under foundations and sidewalks. When you find ants in your house, try to trace where they go after they leave your food or your living area. Check under the sink where the pipes come in, examine electrical outlet boxes, cracked window sills, and cracks in the wall. If you see ants going into one of these places, look under the floor in the basement or around the outside of the house to see if the ants are coming in from the outside. Often, you will find ants near the hot water heater and other warm, moist places in the house. Once you locate the colonies you can make plans to control them. If you cannot find the colony, the ants could be nesting under the house or slab, or it could be a species that nests in the walls.
CONTROL
Nonchemical Control
Seal the house by filling cracks, replacing loose boards, and sealing the plumbing so ants cannot come in from outside. Repair any leaky structures or fixtures to prevent reinvasion. Clean up and remove any food that the ants might eat. Place foodstuff that ants may consume in the refrigerator or in sealed containers. Whenever you find ants, wash them and the area with soapy water. This will kill the ants and remove their food and their scent trails. When you find their nest, dig into it with a shovel, pour in insecticidal soap, and then replace the soil. After several such treatments, the colony will either die out or move somewhere else.
Chemical Control
If you have an ant species that nests outdoors and you treat the colony, this treatment should last until another colony becomes established in a couple of years. If you do not find the colony, and have to rely upon treating the workers when you find them, you may be treating the same colony for years. When you kill a few of the workers you only weaken the colony, but if you do it enough, you eventually will see fewer ants.
If you cannot find the nests and are interested only in getting rid of the ants, apply a residual around the outside of the house. Spray around the foundation of the house in a 6 foot wide swath and up the walls about 3 feet. Be sure to treat any area of the house that touches soil such as pillars, steps, walks, additions, and sheds. As a homeowner, you may buy outside sprays containing carbaryl, propoxur, diazinon, chlorpyrifos pyrethrins, and fenvalerate. Be sure to follow the label for the amount to use for a residual spray. These sprays may damage foliage plants so direct you spray.
After following the sanitation practices listed above, treat the non-food areas that ants frequent inside the house. Treat the corners of the room and walls, around windows and doors, and under and behind cabinets, appliances, and furniture. Use an aerosol spray containing one of the following ingredients: pyrethrin, resmethrin, or chlorpyrifos. Retreat as needed since this method only controls workers.