Ants are good guys in the garden, but bad guys in the house. Learn more about these colony-dwelling insects.
Whether it is a lone ant wandering the countertop or a column on a mission, an ant invasion can be unnerving. Landscaping with organic mulches, movement away from broadcast applications of lawn insecticides and recent mild winters seem to have increased the encounters with these unwelcome visitors.
Ants are Number One
Even though ants primarily live outdoors, they are now the number one indoor pest, displacing cockroaches. Ants are social insects living in colonies usually located near house foundations, and in yards and gardens. When ant workers forage for food for the colony, they often enter houses becoming a nuisance by contaminating food. They are also conspicuous when winged individuals, called swarmers, leave the nest to mate and start new colonies.
Ants invade homes in search of food, moisture and shelter. They are attracted to all foods, especially sweets and grease. Not all food sources are inside, as some ants satisfy their needs by feeding on the sweet honeydew secreted by aphids, scale, mealy bugs and other insects on landscape trees and shrubs.
Common Ants in the Midwest
Several kinds of ants commonly occur in and around homes ranging from the small pavement ant and odorous house ants, to the much larger black field and carpenter ants.
Ant workers, like these odorous house ants, lay down chemical trails as they forage that help direct others to discovered sources of food and water.
The pavement ant is noted for its nest of mounded soil found in pavement cracks, along curb edges and driveways. Pavement ants may forage in the home throughout the year, feeding on most types of food. In winter, nests may be found inside near a heat source, even crawling through ductwork voids.
Odorous house ants can be easily identified because they give off a coconut-like odor when crushed. They nest in mulch, firewood, beneath stones, patio blocks and even in flower pots. Outdoors they especially feed on honeydew secreted by aphids and other insects. Heavy mulch adjacent to foundations has been associated with increased problems with odorous house ants.
Black field ants and carpenter ants are the largest ants found in the Midwest. Black field ants are primarily found in lawns, where they push up large soil mounds, causing unsightly areas and dulling mower blades. Carpenter ants, as the name implies, excavate wood softened by moisture or rot. Unlike termites, they do not eat wood, but remove it to make their nest, sometimes causing structural damage. Piles of sawdust can be telltale signs of a carpenter ant infestation. Correction of high-moisture conditions such as leaking roofs, loose chimney flashing and rotting window sills should be the first step in carpenter ant management. After replacing infested or damaged wood, make a perimeter insecticide spray to protect the home from re-invasion. Since carpenter ants may nest in stumps and firewood, provide a 50-foot buffer for these from the house. Carpenter ants are often accused of killing trees, but likely they have taken advantage of nesting in already rotting wood killed from other causes.
Household Ant Management
A multi-faceted approach is needed for satisfactory ant management. In most cases, ant identification is not needed. The first step is to eliminate sources of food and water attractive to ants. Keep kitchen counters and floors clean and food sealed. Look for other food sources such as garbage “juice” associated with trash cans, and spilled pet food. Dripping faucets and pipes with condensation can be important water sources for invading ants.
Spraying the foraging ants that you see may bring temporary relief, but it often fails to provide long-term, effective control. The workers you see are just a small portion of the overall colony. It is important to eliminate the entire colony for satisfactory control. The most effective approach is to use a bait. Liquid baits seem to be the most appealing to ants. Baits contain only a small amount of insecticide. The ants feed on the bait and take it back to the colony where the slow-acting toxin is shared with the rest of the colony. Place bait directly on the ant trails away from children and pets, and replenish it often. Avoid any perimeter sprays near baits, as these sprays may deter ants from visiting.
Once bait foraging activity subsides, try to determine where the ants might be entering the home. Apply a protective “barrier” around your home by spraying an insecticide up and around the foundation, especially targeting entry points like utility lines and pipes. These sprays will also control other occasional invaders like spiders and cockroaches. Be sure to control honeydew-producing insects on ornamental trees and shrubs.
On an everyday basis, ants go unnoticed while they live outdoors. However, when they invade our humble abodes, they are no longer out of sight, but are a call for action. Don’t panic and take the action!
Is It a Winged Termite Or an Ant?
There are several kinds of ants that may live in and around homes. For most of their lives, both ants and termites are wingless, but they can certainly be confused when their winged stages swarm to start new colonies. Ants can be easily distinguished from termites by several traits, but a hand lens might be needed:
• Ant bodies are hour-glass-shaped (pinched at the waist); termites have thick bodies.
• Ants have elbowed antennae; termites have straight, bead-like antennae.
• Ant wings are clear or brownish; termite wings are milky-white or grayish and longer than the body.
• Although ants are a nuisance, they are far less damaging than termites.
A version of this article appeared in an March/April 2015 print edition of State-by-State Gardening.
Photography courtesy of Douglas Spilker, Gary Graness, and Reiner Pospischil.