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Despite being beneficial in nature, ants and termites become pests when they enter structures and destroy property. Similar to ants, but not closely related, termites have been called “white ants.” Persons attempting to control ants or termites should be able to tell them apart. There are three key features. First, like all insects, ants and termites have three body parts: head, thorax and abdomen. But ants have a thin “waist” (between thorax and abdomen) while the termite’s abdomen is broadly joined to its thorax. At the ant’s waist is one or two expanded segments known as nodes (see pavement ant image below). The number and shape of these nodes are useful features for identifying ant species.

Ants also have “elbowed” antennae; a joint at the middle of each antenna allows it to bend like an elbow, whereas the termite antenna consists of a chain of tiny bead-like segments. The winged forms of ants and termites both have two pairs of wings. However, a termite’s wings are nearly equal in length, whereas ant’s forewings are longer than its hind wings. Termite wings are also laced with many small veins. Ant wings have fewer veins. Another feature of termite wings is that they detach quite easily. Scattered piles of detached wings are often left where termites have swarmed.

Ants are social insects that live in colonies. They cooperate with their nest mates to maintain a caste system of individuals that perform specific tasks. The typical ant colony consists of worker and reproductive ants. Workers are the ants people most often encounter. All workers are female. They construct the nest, gather food, tend the young, move the colony and defend it when necessary.

A ant colony’s reproductives have wings and include one or more egg –producing females, known as queens, and male ants whose only purpose is to fertilize the queens. As in the female-dominated societies of bees and wasps, males are produced seasonally and in relatively small numbers. Once mating has taken place, males serve no further purpose and may be ignored or removed by the female workers.

Ant colonies, like the colonies of bees, wasps and termites, function with mechanical efficiency to accomplish one goal: reproduction. Workers produce no offspring. They “sacrifice” their own procreation to maximize the number and survival of offspring produced by the queen. This “strategy” makes sense because the workers within an ant colony are so closely related to the queen that, in essence, raising the queen’s offspring is like raising their own.

An ant develops through egg, larva, pupa and adult stages. The white “ant eggs” carried by workers when an ant colony is disturbed or moving are not the eggs but the pupal stage of complete metamorphosis. Ant eggs are almost microscopic. The larvae that hatch from them are helpless, grub-like young that the workers must feed and care for. A larva grows, enters the pupal stage and later emerges from its cocoon as either a worker or reproductive.

Worker ants can live for a few years; queens for perhaps a dozen or two. But ant colonies often go on for decades with workers endlessly scouring the landscape for food, laying down and following chemical odor trails to food sources, defending against predators and rival colonies, hatching more workers and expanding the colony, and periodically producing winged reproductives commonly known as “swarmers.” The reproductives fly off to establish colonies of their own.

While ants contribute positively by conditioning the soil and preying upon termites, caterpillars and other pests, ants themselves often become pests. Their nests and mounds are considered unsightly where they are not wanted, and ant nests in structures can damage property. Ants consume and contaminate food. And some species sting people, pets and livestock, occasionally causing death.


PAVEMENT ANT (Tetramorium caespitum)

Probably the most common ant in structures, the pavement ant, is so named because it excavates an underground nest and pushes the soil into conical mounds along rocks, concrete slabs, sidewalks and driveways. Nests also can be found in logs, mulch, wall and floor voids, and insulation. Pavement ants are dark brown-black and about 1/6-inch long. They forage 30 feet or more from their nest in search of a variety of foods, including grease and oils, seeds, sweets and honeydew (the sugary waste of aphids). They are often seen indoors after heavy rain drenches their underground territories.

ODOROUS HOUSE ANT (Tapinoma sessile)

This 1/8-inch long, brownish-black ant can be confused with the pavement ant, until the odorous house ant is crushed, releasing an odor like rotten coconut. In recent years it has become an increasingly common household invader. Nests are found under rocks, boards and other debris, and in floor and wall voids. These ants will move indoors during rains and in the fall. They feed on sweets, honeydew, plant and fruit juices, meat and dairy products.

SMALL HONEY ANT (Prenolepis imparis)

When small (to 1/8-inch), dark ants are found indoors, it’s likely they are either pavement ants, odorous house ants or small honey ants. Honey ants nest in voids under concrete slabs, flooring and in walls. They feed on honeydew, honey and other sweet liquids, plant juices, and various foods and beverages. Small honey ants seem to prefer lower temperatures than other ants. They may be the first and the last ants seen each year, disappearing during the heat of summer.

CARPENTER ANT (Camponotus spp.)

Illinois ’ largest ants are known as carpenter ants because they nest in wood. Nests consist of numerous tunnels chewed in logs, stumps, tree trunks, firewood, decks and porches, window and door frames, wall voids and foam insulation. The ants expel piles of sawdust, dead ants and parts of dead insects from the nest and these can help inspectors determine the nest’s location. Indoor nests are usually “satellite” nests connected to the colony’s main nest outdoors. Satellite nests are often established in wood where moisture problems exist (e.g., around leaking pipes, inadequately sealed window frames and roof leaks). The common black carpenter ant (C. pennsylvanicus) is a dull black ant with workers of various sizes up to ¾-inch long. Other species are black or dark reddish-brown. They do not eat wood but forage for human foods, including sweets, meats and grease, as well as honeydew, and live or dead insects. A fact sheet on carpenter ants is available at: http://www.idph.state.il.us/envhealth/entpestfshts.htm

LARGER YELLOW ANT (Acanthomyops interjectus)

Also called the citronella ant, this ant has a citrus-like odor when crushed. It is a yellow-brown ant up to ¼-inch long. These ants forage at night, tending the subterranean aphids and mealy bugs they “milk” to obtain honeydew. They do not feed on human foods. They are usually noticed when colonies move indoors in winter, and in spring when the winged reproductives (see image above left) are produced and often mistaken for termite swarmers. Their nests are found under rocks, logs, stumps, concrete slabs and in crawlspaces. Piles of soil may accumulate near the nest entrance.

PHARAOH ANT (Monomorium pharaonis)

The tiny (1/12-inch) pharaoh ant is yellow to reddish-brown. It is nearly identical to the thief ant (Solenopsis molesta). However, the pharaoh has an “antennal club” consisting of three expanded segments on the end of its antenna, while the thief ant has a two-segmented antennal club. Pharaoh ants nest in voids in floors, walls and ceilings. They often infest large buildings. In hospitals, these ants pose a health risk because they can carry infectious bacteria from the warm, moist areas they inhabit, to intravenous fluids, blood and wounds. The pharaoh ant also presents a problem for pest management. The colonies of this ant do not spread by swarming, but instead by “budding,” breaking apart and establishing sub-colonies in new locations. This process can be triggered when the colony is stressed by the application of repellent liquid or dust pesticides. Colonies can be very large, some containing more than 100,000 ants.



Maximum Worker Size (inches)


Number of Nodes

Maximum Colony Size

Swarming Time

Pavement Ant


dark brown




Odorous House Ant






Small Honey Ant


dark brown




Carpenter Ant






Large Yellow Ant






Pharaoh Ant





No Swarm


Often the first reaction to seeing a line of ants trailing inside the home is to grab a can of pesticide and spray them. This strategy usually results in a few dead ants. Unfortunately, it treats only the symptoms of an ant problem. Routine spraying of ants and their trails rarely provides the cure, since there are a lot more ants where those came from.

For most integrated pest management programs, including those for ants, exclusion is the first line of defense. This involves taking steps to prevent pests from entering the structure. Most often, ants are nesting outside a structure and make periodic “raids” indoors in search of food. Sometimes they enter the structure and establish nests inside it. Inspect for ant entry points around the foundation outside, and inside crawlspaces and basements. Apply a sealant, such as silicone caulk, to gaps where ants are entering the structure, and to potential entry points.

Another weapon in the pest management arsenal is sanitation. For ant management this means keeping vegetation, mulch, landscape timbers, firewood and debris away from the structure’s foundation, as these items harbor ants and the insects some ants feed on. Moisture also attracts insects, so leaky faucets and pipes, faulty grades, clogged gutters and downspouts should be repaired. Ants usually enter structures in search of food. So sanitation indoors means keeping foods tightly sealed.

Making food unavailable to ants not only discourages them from establishing trails into a structure, but makes them more likely to accept baits. Ant baits can be purchased at discount, hardware, garden and grocery stores, and their proper use can often eliminate ant problems. Ant baits are pesticides available in solid, gel and liquid forms. Some baits contain insect growth regulators that prevent immature ants from becoming adults. Most contain slow-acting toxicants mixed with food. Apply baits according to label directions where ants are seen, especially where they are trailing. If ants accept the bait, larger numbers may arrive to feed on it. The mass of ants may be alarming, but refrain from spraying them. More ants taking the bait often results in quicker and better control. Spraying the ants defeats the purpose of the bait and can prolong the problem.

Ants ingest the bait and carry it back to the nest. There they feed the bait to other ants including immature ants and the queen. If enough bait placements are made and enough ants feed on the bait, the colony will eventually be unable to feed itself since not enough workers will survive to gather food. Dozens of bait placements may be needed to control ants with large colonies such as those of pharaoh ants.

Unfortunately, ant baits don’t work against all types of the ants all of the time. Identifying the ants involved can make it easier to select the most effective bait. Even so, some ant species do not respond well to baits. Citronella ants, for example, do not respond to baits because they feed exclusively on honeydew excreted by aphids and mealybugs. Species that can be baited successfully often prefer different baits at different times because the ants’ nutritional requirements change throughout the season as the colony grows. So if the ants do not take the bait, try a different bait. Also, in areas where baits are placed, do not apply other types of pesticides, such as sprays that can contaminate baits and repel the ants. Indoors, vacuuming ants is often better than spraying.

Conventional pesticides, such as liquids, dusts and granules, can be part of an ant management plan. Always read the label and follow label directions. Liquid pesticides are best used for ant control outdoors. They can be applied as a barrier treatment to the ground inside a crawlspace or around the perimeter of the foundation. Again, this type of treatment rarely results in eliminating the ants, but does afford some degree of protection by repelling or killing ants that attempt to enter the structure. Sometimes it is necessary to inject liquid insecticides into the soil beneath concrete slabs, crawlspaces and around foundation walls. This is one reason to consider hiring a pest management professional more experienced and better equipped to do this type of treatment.

Granular formulations also can be used outdoors, applied to soil, gravel or mulch around the foundation. Many granular products require drenching with water to activate the granules and to work them into the substrate. “Broadcast” applications of granules and other pesticides should not be made to entire yards. Ants are beneficial insects, and pesticides should only be used against ants known to be entering a structure. Note that some ant baits are available as granules and these should not be confused with other granular formulations designed to kill ants on contact. Once again, read the label.

If the nest can be located, liquid or dust formulations should be applied directly to it. This is often the surest way to get rid of ants. Of course, the difficultly of this method lies in finding the nest. Trailing ants should be observed and followed. Ants carrying food parcels will inevitably be heading back to the nest to share their prize with nest mates. The list of possible nest locations can be narrowed by identifying the ant. Inspecting after dark is sometimes best, as some species are more active at night.

Once an ant nest is discovered, it can be drenched with a liquid pesticide, or treated with a dust formulation. Dusts can also be used indoors. Apply them wherever nests might be present such as wall voids, voids within window and door frames, behind baseboards and around the edges of wall-to-wall carpeting, behind electrical switch plates and socket housings, behind cabinets – but not above drop ceilings, not around food storage and preparation areas, nor in any place accessible to children and pets. Note also that most dusts are long-lasting pesticides that should be applied thinly and rarely need to be reapplied.

Ant management often requires the use of more than one method of control. By using the techniques of exclusion and sanitation described above, you may be able to keep ants out without using pesticides. However, if you find it necessary to use pesticides, exclusion and sanitation should still be a part of the plan. Remember that to eliminate an ant colony almost always requires elimination of the queen(s). This can be accomplished with ant baits, or by treating the nest with a liquid, dust or granular pesticide labeled for this type of use.

Sometimes an ant infestation is difficult to control, even for professionals. Consider hiring a pest management professional, especially if you are unsure about your ability to identify the ant, correctly diagnose the problem and properly employ the required control methods.

NOTE : When pesticides are used, it is the applicator’s legal responsibility to read and follow directions on the product label. Not following label directions, even if they conflict with information provided herein, is a violation of federal law.

Illustrations courtesy of Alex Wild ( University of California , www.myrmecos.net ), Jim Kalisch ( University of Nebraska) and the Ohio State University.

For more information, contact the Illinois Department of Public Health, Division of Environmental Health, 525 W. Jefferson St., Springfield, IL 62761, 217-782-5830, TTY (hearing-impaired only) 800-547-0466.

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Environmental Health Home

Illinois Department of Public Health
535 West Jefferson Street
Springfield, Illinois 62761
Phone 217-782-4977
Fax 217-782-3987
TTY 800-547-0466
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