Send Letter to Editor

Wisconsin Natural Resources magazine

Wisconsin Natural Resources magazine

June 1999

Illustration © ClickArt, T/Maker Company/Broderbund Software, Inc.


The only cure for an infestation of these industrious social insects is more knowledge.

Holly Prall

Antipasto: What ants eat
Anteroom: Where ants live
Anticipation: How ants prepare for the next generation
Antiheroines: Carpenter ants in your home
Antithesis: The other side of the story
Anticlimax: How to control household ants safely and effectively
Ant or termite – a comparison chart
Know your ants – an identification chart

Few people bother to consider the world of ants – until it appears that the ants of the world are mounting a colossal attack on the kitchen and environs. In midsummer, you may have noticed ants invading the countertop cookie jar or Fido's food dish on the floor. In fall, streams of the industrious insects will put the bite on a bar of bathroom soap. What about those pale, winged ants that suddenly appear in a little cloud in the basement?

Are these serious infestations? Though some may think "an ant is an ant is an ant," in reality, there's great variety in the ant world. Knowing the differences will increase your enjoyment of nature, and also help you mount a successful eradication campaign, should one become necessary.

Antipasto: What ants eat

Ants (family Formicidae) have become such successful insects because they are highly adaptable, with many species able to eat just about anything. The seed-eating Grease Ant (Solenopsis molesta), though among the tiniest of ants, earns its nickname "Thief Ant" by sneaking into the nests of larger ants and eating their larvae. Carpenter Ants (Camponotus spp.) eat other insects and a variety of sweet foods, but they definitely do not, like termites, eat wood.

A favorite food of carpenter ants and many other species is honeydew – the sugary excretion of sap-sucking insects such as aphids, scale insects, treehoppers, and leafhoppers. The False Honey Ant (Prenolepis imparis) so loves to gorge on honeydew and plant juices that an ant may become stuffed to the point where it has difficulty walking.

In return for honeydew, which may be excreted on demand by the aphids, ants protect their aphid "herds," aid them in dispersal, and prevent a build-up of honeydew in their vicinity, thus keeping the insects free of fungal disease. Some ants, such as the Larger Yellow Ant (Acanthomyops interjectus), a nocturnal, subterranean dweller, live exclusively by tending root aphids for honeydew and perhaps eating some of these soft insects. This pale ant is not a serious pest even if it finds its way inside the house foundation. Ants may also consume the nectar of flowers or other plant juices and secretions.

Know your ant! If you can't i.d. the species yourself, capture an ant, preserve it in rubbing alcohol and take your specimen to a pest control expert.

© Van Waters & Rogers, Inc.
Larger yellow ant.© Van Waters & Rogers, Inc.

When the outdoor foods they like most are in short supply, or competition is great, as in mid- to late summer, many ants will forage indoors for a variety of sweet, greasy, and protein-rich foods. The "scout" ants use pheromones – odorous chemicals – to communicate the location of a large food find with the colony. The scout first has a bite to eat, then promptly returns home, laying down a pheromone trail that stimulates the other ants to follow.

When the other ants leave the nest, often in numbers proportional to the amount of pheromone released, they wave their antennae in the air to find traces of pheromone vapor. Scouts of some species, such as grease ants and Pharaoh Ants (Monomorium pharaonis) – a stubborn pest known to eat such unusual foods as toothpaste and soap – add their own traces to the trail as they return to the nest site. Because the trail is constantly renewed, a conspicuous, persistent track of many hundreds of ants may develop.

This style of foraging, known as mass recruitment, allows the tiny insects to efficiently exploit any food find before the scouts of any other species discover it. Some species of Field Ants (Formica spp.) have developed their own highly efficient foraging system: They make broad "ant highways" chemically marked and cleared of vegetation and debris.

Anteroom: Where ants live

Within limits, ants love heat. Most ants function poorly below 20C (68F) and not at all below 10C (50F), although the cold-tolerant false honey ant has been known to forage at temperatures close to freezing. In Wisconsin, many ants of different varieties have adapted to their environment by living in the soil or in other locations that allow them to keep the temperature and humidity at favorable levels. The ants move to deeper chambers or special winter nests when the weather is cool; their respiration may slow and reproduction may cease.

Ant nests vary in depth and in primary orientation – horizontal or vertical. For example, the notorious pesky ants that tend aphids on the roots of plants, such as the Cornfield Ant (Lasius alienus) and the pavement ant, often have mainly horizontal tunnels. The cornfield ant is known for hatching the corn root aphid and transferring it from grasses to growing corn. These same ants foster strawberry aphids and thereby undermine strawberry plants. The Pavement Ant (Tetramorium caespitum) has a reputation for girdling plant stems and eating their sap, and for storing seeds in its nest.

Most species in Wisconsin do not live in the open soil. Some nest under flat stones, like the pavement ant; or under the bark of a tree, like the carpenter ant. Other species build mounds. The mounds are not to be confused with craters – the loose piles of dirt pellets kicked up by soil-dwelling ants during their excavations.

Illustration © ClickArt, T/Maker Company/Broderbund Software, Inc.

Rocks and bark warm quickly in the sunlight, and a raised mound has more exposed surface for the sun to intercept. Thus, in all of these nesting sites, ants catch more sunlight for their colonies to use in the early spring. Ants also move the larvae around in the nest throughout the day to ensure the proper conditions for the developing brood.

The pharaoh ant, introduced from the tropics, can live only indoors in heated buildings. A "tramp species," it often lives in close association with people and is sometimes carried in their belongings from place to place. This opportunistic nester has taken advantage of its small size to exploit unusual nesting sites such as the space between layers of linens or sheets of stationery. Another opportunistic nester is the Odorous House Ant (Tapinoma sessile), which, despite its name, is primarily an outdoor nester. It sometimes colonizes bird nests, plant stems, and spaces beneath urban debris.

Anticipation: How ants prepare for the next generation

After a certain length of time, ranging from a single warm season to five or more years, the colony matures and enters the reproductive stage, when sexual forms begin to be produced. A carpenter ant colony, for example, may reach maturity when it contains 2,000 or more workers and is three to six or more years old. At maturity, it produces 10 to 400 winged reproductive ants that will emerge and swarm during the spring in what is known as a nuptial flight.

Queen ants, which may be twice as large as workers, have two pairs of wings (front longer than back) and a large hind section, or gaster. The males are typically slightly smaller and also winged. Generally, they play no role in the daily life of ant colonies and die soon after mating with a virgin queen, often by being devoured by birds (ants' main predator), other ants, or other insects. When the queen returns to earth some distance from the nest where she matured, she chews off her wings and digs a small hole, sometimes beneath the bark of a tree, log, or stump. Here she will lay 15 to 20, even as many as 27 eggs.

The microscopic eggs pass through two main stages of development before becoming adults – larvae and pupae. The larvae are grublike, blind, and often shaped something like a crookneck squash. The soft, colorless pupae resemble the adult in form. The queen nourishes them with nutritive juice formed from stored fat and the breakdown products of her huge flight muscles. For the two to 10 months it takes for them to mature, she never leaves the nest. Finally, the first workers mature, and begin to care for the queen, as well as her new brood. Nest building must also be done. The loss of even a few foraging ants during this period would be disastrous for the young colony. If the colony survives this initial, sensitive period, it is likely to continue growing at an accelerated rate.

Some species, such as the pharaoh ant and the odorous house ant, establish new nests exclusively by a process known as budding. A satellite nest buds from an established one when a few workers, often with one of the colony's many queens, leave to set up housekeeping at another location, again making use of chemical trails. With this method, the queens are never exposed to the risks of a nuptial flight, but instead mate inside the nest and walk to their new home. Most carpenter ant invasions are established by budding, when part of a colony walks in and builds a nest indoors.

Antiheroines: What you have if carpenter ants working on your home

Carpenter ants commonly move inside between November and early March. You may hear their rustling in the walls at night. If the colony is active all year, the ants are likely to be in walls, door voids, ceilings, or other heated areas of the house. Other common areas are under outside siding and in wood-soil contacts near the foundation carpenter ants generally choose softened or weak wood, with a moisture content of 15 percent or greater, sometimes under bathroom floors.

In nature, they occupy dead portions of standing trees, stumps, or logs, or burrow under fallen logs or stones. Silver maples are commonly infected and white pine not at all. Ants in outdoor trees may send out scouts to establish satellite colonies in firewood, lumber, wood debris, or possibly on steps, porches, decks and columns. Vegetation, utility wires and phone wires that touch the home often provide bridges from tree to house.

Field ants have "soldiers" that are capable of biting both insect and human invaders, but ants have means of defense. Many species secrete poisonous substances from glands to ward off intruders. Formic acid, excreted by field ants, is used in combination with the lemony smelling citronella by the larger yellow ant. An unpleasant odor described as "rotten coconuts" is emitted by odorous house ants when disturbed or crushed.

Antithesis: The other side of the story

Ants play an important part in insect control, in part by keeping more harmful pests away from the plants they patrol. Like spiders, indoor ants are likely to eat flea and fly larvae and other pests. Field ant species, for example, also prey on bed bugs, moths, young silverfish, and subterranean termites. Having ants patrolling your home's borders may be important in controlling termites.

In the woods, carpenter ants help decompose trees. Ants of all kinds aid in recycling nutrients. Organic matter accumulated in ant nests can add nutrients to soil and improve its structure. Digging by ants loosens the soil, increasing its porosity and making it easier for air, water, and plant roots to penetrate.

Consider the humble ant's positive contribution to the health of the environment. Then plan your control strategy accordingly. The guidelines below should help you safely fend off ant invaders.


How to control household ants safely and effectively

1. Identify the type of ant. Know your quarry! Control measures differ for different types of ants. A magnifying glass will aid in identification. You may need to capture an ant and preserve it in rubbing alcohol to examine it. For further help in identifying ants, submit a sample to your local extension service for a pest control company.

2. Is action necessary? Consider the type of ant, the number you see, where you see them, and other pertinent factors, such as the season. You may decide that you can put up with an occasional field ant in your kitchen in the summer, for example. But other species may cause serious problems in time: The pharaoh ant spreads quite rapidly. And while a few carpenter ants in the kitchen may simply be foragers from an outdoor nest, the repeated appearance of carpenter ants in other rooms suggests they are nesting in damaged or rotting wood – possibly a window frame.

3. Try simple measures first. Deny ants easy nest sites, food and water sources. In the kitchen, keep counters, appliances and floor surfaces clean; remove garbage daily; remove organic wastes from containers before discarding ; and rinse recyclables before storage.

Keep foods in glass jars or plastic containers with tight-fitting lids. A water moat, such as a pie pan containing soapy water, can be used to prevent ants from reaching sticky foods like honey, or other items such as plants. Sticky barriers such as Tanglefoot can also be used on the legs of outdoor plant stands, on foundation walls, or around the trunks of roses or trees to keep off aphid-promoting ants. Throughout the house, seal any cracks where ants may be entering.

To prevent a carpenter ant problem, remove or replace all damaged or decayed wood in your house. Ventilate attics, bathrooms and damp areas. Keep rain gutters clear of debris. Remove tree stumps and dead branches close to the house. Store lumber and firewood above the ground and away from the house

4. Follow the trail. Take up the rear and follow the trail of ants to find the entry point or nest. Try killing ants you see with soapy water, and eradicating the trail with soapy water or a mild solution of vinegar and water. Seal the entry with silicone caulk (duct tape also makes a good temporary sealant).

If ants can be traced back to an outdoor nest, drench the nest several times with hot, soapy water every few days until activity ceases. Carpenter ant nests can be removed or treated with insecticide sprays containing pyrethrum.

If you do not see a trail, set up a stakeout: Put out a food the ants like, then watch and wait – at night, for carpenter ants. Outdoor nests may be under siding, on wooden porches, or at wood-soil contacts near foundations. Indoor nests may be found in rotten woodwork as well as wall voids, hollow-core doors, foam insulation, or hollow beams. To locate openings into the nest, look for small piles of coarse sawdust and insect parts known as frass.

If carpenter ants are nesting in a void or hollow space, apply some form of insecticidal dust directly to the nest. Drill holes for access as necessary. A plastic squeeze bottle filled about 1/3 to full may be used to force the dust into the nest spaces. Nonglassified diatomaceous earth and silica gel work by attacking the waxy coating of the ant, causing it to lose moisture and eventually die. Wear goggles and a dust mask when applying dusts. Boric acid or a combination of silica gel and pyrethrums for quick knockdown, may also be used. A small, light application of dust is best. If the dust is too thick, the ant will simply avoid the area. After applying a dust, make sure that all cracks and holes are well sealed, and that the area is kept dry.

For exposed nests try sucking up the ants with a vacuum. A liquid or aerosol spray for ant and roach control, such as one containing pyrethrum, may also be used. Be sure it is labeled for indoor use.

If you can't find a nest or point of entry, spray a chemical barrier around the house, windows and doors in a two to three foot wide band.

5. Set the bait and wait. For many species, baits are the best option when indoor nests cannot be located or are inaccessible, but the baits can take several months to work. Ant baits work as food is shared in the nest among all the workers and the developing brood. It is important that baits are mild enough so weakened ants will keep coming for more, but strong enough to eventually kill the whole colony. Since pupae don't feed from the bait, you may need to periodically retreat the area to reduce carpenter ant populations.

Match bait materials to the ants' food preferences. Different baits are formulated against sweet-feeding ants; while others control protein feeders. A mixture of one-quarter teaspoon boric acid to about 4 tablespoons of a food ants like – honey, syrup, or peanut butter – can be placed on jar lids, small pieces of cardboard, or in straws set where ants are commonly found. Sealed, labeled jars containing a boric acid, food solution with holes punched in the top may also be used. Effective baits for other species like carpenter ants of pharoah ants may only be available from licensed pest control companies.

Ant or Termite?

Termites belong to the Order Isoptera, and their closest relatives are roaches. Though sometimes confused with ants, termites differ in many important ways:

Carpenter ants


Eating habits Sweets, honeydew and other insects; chews but does not eat wood.Eats wood; can digest the cellulose due to protozoan living in digestive tract.
Foraging habits Ants of many species are commonly seen foraging in the open, some most often at night.Avoid light; may live inside own food or travel in tunnels through the soil or covered runways to forage on dead wood.
Indoor tunnels Damage to wood is caused by moisture or dry rot with only local damage to sound wood. Piles of coarse sawdust mixed with insect fragments (called frass) may be pushed out of slit-like nest openings and fall on surfaces below.
Social structureAll workers are females. Grub-like whitish larvae and soft-bodied pupae are helpless and must be carried off by adults if nest is attacked.Males participate in the colony work. Eggs hatch to creamy-white nymphs, molt several times and participate in work when half-grown.

Holly Prall is a freelance science writer from Greensboro, North Carolina. She volunteers teaching children at a neighborhood program.