CARPENTER ANTS

by Mike Potter, Extension Entomologist

University of Kentucky College of Agriculture

"I keep seeing big, black ants in my house, especially in the kitchen and bathroom. I spray the ones I see, but they keep coming back. What kind of ants are these, where do they come from, and how do I get rid of them?"

USDA Insect and Plant Disease Slide Set

These are the questions typically asked by homeowners who have carpenter ants. Carpenter ants are one of the most common ants found in Kentucky. They are also one of the most difficult to control. This publication will help you determine if you have carpenter ants, and provide tips on how to control them.

Biology and Habits

Carpenter ants, vary in size and color but are usually large (1/4-1/2 inch) and blackish. Occasionally, swarms of winged carpenter ant reproductives will emerge inside a home. Carpenter ant swarms usually occur in the spring and are a sure sign that a colony is nesting somewhere inside the structure.

University of Kentucky Entomology

University of Kentucky Entomology

Winged carpenter ants can be distinguished from termites by their larger size and shape of their antennae, waist and wings.

Besides being objectionable by their presence, carpenter ants damage wood by hollowing it out for nesting. They excavate galleries in wood which have a smooth, sandpapered appearance. Wood which has been damaged by carpenter ants contains no mud-like material, as is the case with termites. Shredded fragments of wood, similar in appearance to coarse sawdust, are ejected from the galleries through preexisting cracks or slits made by the ants. When such accumulations are found (typically containing dead ants and bits of insects which the carpenter ants have eaten), it's a good indication that a carpenter ant nest is nearby. Oftentimes, however, the excavated sawdust remains hidden behind a wall or in some other concealed area.

Carpenter ants nest in both moist and dry wood, but prefer wood which is moist. Consequently, the nests are more likely to be found in wood dampened by water leaks, such as around sinks, bathtubs, poorly sealed windows/ door frames, roof leaks and poorly flashed chimneys. Nests are especially common in moist, hollow spaces such as the wall void behind a dishwasher, or in a hollow porch column. Since there often will be no external signs of damage, probing the wood with a screwdriver helps reveal the excavated galleries. Another technique for locating hidden nests is to tap along baseboards and other wood surfaces with the blunt end of a screwdriver, listening for the hollow sound of damaged wood. If a nest is nearby, carpenter ants often will respond by making a " rustling" sound within the nest, similar to the crinkling of cellophane.

Carpenter ants may establish nests in a number of different locations. It is important to realize that these locations can be either inside or outside the structure. Carpenter ants actually construct two different kinds of nests: parent colonies which, when mature, contain an egg-laying queen, brood and 2000 or more worker ants, and satellite colonies which may have large numbers of worker ants but no queen, eggs or young larvae. The carpenter ants inside a home may have originated from the parent colony or from one or more satellite nests. For example, the ants may be coming from the parent nest located outdoors in a tree stump, landscape timber or woodpile, or from one or more satellite nests hidden behind a wall in the kitchen or bathroom, or perhaps from wood dampened by a roof leak in the attic.

The extent and potential damage to a home depends on how many nests are actually present within the structure, and how long the infestation has been active. Although large carpenter ant colonies are capable of causing structural damage, the damage is not normally as serious as that from termites. In some cases, the damage may be relatively insignificant, but this can only be determined by locating and exposing the nest area.

Control

The best way to control carpenter ants is to find and destroy the nests. This is often easier said than done. Recent studies have shown that carpenter ants follow distinct scent trails between the satellite colonies and the parent nest. Carpenter ants also rely on scent trails to recruit their nestmates to food. With patience and a little effort, homeowners can use this trailing behavior displayed by carpenter ants to locate and eliminate the nests.

When carpenter ants are observed, don't spray them; instead, feed the ants small dabs of diluted honey placed onto the back (nonsticky side) of pieces of masking tape. The best time to do this is late at night since this is when carpenter ants are most active. After the ants have fed on the honey, follow them on their journey back to their nest. Be patient-- eventually the ants will disappear behind a baseboard, cabinet, or into some other concealed location such as the hollow space (void) within a wall, door casing, or porch column.

Treat wall voids and other hidden spaces where ants are entering by carefully drilling a series of small (1/8 inch) holes and puffing boric acid (available at most hardware stores) into the suspected nest areas. The boric acid powder will disperse in the hidden void and contact and kill the ants. If you suspect the nest is in a wall, drill and treat at least 3-6 feet on either side of where ants are entering so as to maximize the chances of contacting the nest. Carpenter ants prefer to travel along wires, pipes and edges. If you suspect the nest location is in a wall, also treat behind pipe collars and behind --not in-- the junction box for electrical switch plates/receptacles. NEVER SPRAY LIQUIDS OR INSERT METAL-TIPPED DEVICES AROUND ELECTRICAL OUTLETS!).

As noted earlier, carpenter ants seen in the home may actually be nesting outdoors, foraging indoors for food and/or moisture. Consequently, the homeowner may end up following the ants they have baited with honey out of the house and into the yard, possibly to a nest located in a stump, or under a log or railroad tie. Once the outdoor nest is discovered, treatment can be performed by spraying or drenching the nest with an insecticide such as carbaryl (Sevin), diazinon, or chlorpyrifos (Dursban). If outdoor nests are suspected, the homeowner should also inspect around the foundation of the building at night with a flashlight, especially around doors, weep holes and openings such as where utility pipes and wires enter the structure. The baiting approach using honey can also be used to trace carpenter ants which are foraging outdoors back to their nest.

Tips When Calling a Professional

Oftentimes, it will be difficult or impossible to locate and destroy the carpenter ant nest(s). In this case, the homeowner may wish to call a professional pest control operator. Pest control companies approach carpenter ant problems differently. Some attempt to locate the nest and selectively treat only in specific areas. Other companies take more of a "shot-gun" approach, drilling and dusting as many potential wall voids and nesting sites as possible. Most companies also apply a perimeter spray treatment around the outside foundation of the home in an effort to temporarily prevent reinvasion. The approach which should not be used is simply to spray each month where carpenter ants are seen. If no effort is made to locate the nest(s) or probable nest areas, the problem will most likely continue.

Typically, there will be wide differences in price depending on the company and amount of effort expended. Since carpenter ant problems are not always solved on the first attempt, the type of guarantee and reputation of the company should be factored into the purchasing decision.

Carpenter Ant Prevention

A number of steps can be taken by homeowners to reduce the potential for future carpenter ant problems.

1. Correct roof leaks, plumbing leaks and other moisture problems which will attract carpenter ants.
2. Eliminate wood-to-ground contact such as where landscaping has moved soil or mulch up against the wood siding of a home.
3. Clip back tree limbs and vegetation touching the roof or siding of the house. Limbs and branches serve as "bridges" between carpenter ants nesting in a dead tree limb and the structure.
4. Seal cracks and openings in the foundation, especially where utility pipes and wires enter from the outside.
5. Stack firewood away from the foundation and elevate it off the ground. Never store firewood in the garage or other areas of the home, as firewood is a prime nesting area for carpenter ants.

Carpenter Ants
by Barb Ogg, Ph.D., Extension Educator

Printable

Carpenter ants are important in the balance of nature because they burrow and nest in dead trees and enhance decay of the wood. They achieve pest status when a colony invades and damages the integrity of the wood within a house. This fact sheet will explain how the biology and behavior of carpenter ants relate to control strategies when a homeowner is faced with this problem.

Description and Habits: The black carpenter ant, Camponotus pennsylvanicus, is the most common carpenter ant species in Nebraska. Foraging workers are 1/4 inch to 5/8 inch and black in color. Another species, the rust-colored carpenter ant, Camponotus ferrugineus, is a bit smaller and has a reddish-orange thorax with a black head and abdomen. The most diagnostic characteristic of all carpenter ants is they have a one-segmented pedicel (the segment between the thorax and the abdomen). The profile of the thorax is evenly rounded and not bumpy.

Most carpenter ant workers are polymorphic—which means they are different sizes. Entomologist refer to larger workers as "major" workers and the smaller workers as "minor" workers. Each colony has at least one "queen," the reproductive member that produces all additional members of the colony. There may be more than one queen in a colony.

When a colony gets very large (six- to ten-years-old and has more than 2000 workers), it may produce winged reproductives, called swarmers. They are often produced during the summertime and may overwinter in the colony. In Nebraska, we have people reporting swarms of the rusty-colored carpenter ants during periods of warmer weather from February to April. The black carpenter ants swarm a bit later and is more commonly observed from March to June, but we have seen swarming of both species during most warmer months. The males often emerge first and are smaller than the females.

After mating, a single queen seeks out a suitable nesting site and lays only a few eggs that hatch into maggot-like larvae. She cares for the larvae that become the colony's first workers, forage for food, and feed the young while the queen continues laying eggs.

The diet of carpenter ants is quite varied and includes living and dead insects, honeydew from aphids, sweets, meat, and fats. They do not eat wood. Workers leave the colony in late afternoon or early evening, forage during the night, and return to the colony in the early morning hours.

Carpenter ants carry food back to the nest intact or ingested and later feed it to non-foraging members in the nest. These ants may forage up to 100 yards from the nest to search for food. Carpenter ants may become pests in houses by foraging for food. The greatest concern, however, is they may cause serious damage to wood in the structure. Unlike termites, they do not feed upon wood, but merely use it as a place to nest.

Carpenter ants construct their nests in hollow trees, logs, posts, landscaping timbers, and wood used in homes and other structures. These ants prefer to infest wood that is moist and rotting, but wood that has been wet previously, may be soft enough to allow carpenter ants to hollow it out and produce a colony. Certain parts of a house such as: Around and under windows, roof eaves, decks, and porches are more likely to be infested by carpenter ants. Refer to the diagram on the back for the most common problem areas of a home.

Carpenter ants will use an old abandoned nest or wood that has been "hollowed out" by termites. Nests may be located in hollow doors or small void areas produced during construction.

Carpenter ants may move from decaying portions of the wood into sound lumber in the process of enlarging the nest. They cut galleries with the grain following the softer parts of the wood. The ants leave harder parts of the wood as walls separating the tunnels and cut openings in these walls to allow access between tunnels. Access to the outside may be through natural openings, or the ants may cut openings where none exist naturally.

Carpenter ants keep occupied galleries clean. They remove wood in the form of a coarse sawdust-like material, which they push from the nest. This often results in a cone-shaped pile accumulating just below the nest entrance hole. This pile may include, in addition to the wood fragments, other debris from the nest, including bits of soil, dead ants, parts of insects and remnants of other food they ate.

Certain parts of a house are more likely to be infested by carpenter ants. Refer to the following diagram for most common problem areas of a home. 

Control

Colonies of many ant species can be controlled with baits, but carpenter ants have such a varied diet, baits are not always successful. Spraying insecticide on foraging workers is of limited value because the queen will continue to produce more young.

The secret to controlling carpenter ants is direct treatment of the colony. Look for the piles of sawdust to locate the entrance. Because worker ants move from the nest to forage for food, their movements may lead to your discovery of the nest opening. Inspect the entire structure and surrounding grounds, because the nest or nests may be outdoors as well as in the structure.

Once you find the colony, you can completely eliminate the infestation by removing all the infested wood. But, if there is a contributing moisture problem, be sure to fix it first. If you cannot remove the infested wood, you can inject a dust formulation of an appropriate insecticide into the wall void. A dust formulation is best, because the ants walk through the dust and contaminate the colony. Introduce the dust into the nest through the entrance hole using a hand duster with a tube with a tip that fits snugly in the entrance. It may be necessary to enlarge the hole to fit the duster. You can make a duster from a flexible plastic bottle equipped with a tube tip. Fill the bottle no more than one-third full, insert the tip in the entrance hole, and inject the dust by alternately squeezing and releasing the pressure on the bottle. A dust containing 5 percent carbaryl (Sevin®) is recommended for this treatment. Only use carbaryl (Sevin®) dust in wall voids or other areas where the dust won't come into contact with humans or pets. Be sure to store any leftover insecticide in its original container with the label intact.

To prevent further carpenter ant infestations, trim all trees and bushes so branches do not touch the house and correct moisture problems such as leaky roofs and plumbing. Paint and/or seal exposed wood construction before it becomes wet. Replace previously ant- or termite-infested wood, rotted, or water-damaged wooden parts of the structure and eliminate wood/soil contacts. Remove dead stumps on the property and store firewood off the ground and away from the structure.

Carpenter ants will not kill living trees, but openings in living trees are attractive to carpenter ants; these openings should be closed. Stacks of firewood and old dead tree stumps also attract carpenter ants. The longer wood remains undisturbed, the more likely it will become infested. It is better to keep on hand only the supply of firewood you plan to use during one heating season. Store the wood off the ground and away from the house. Spraying of firewood to protect it is of little value and is not recommended. This resource guide was updated April 20, 2001

CARPENTER ANTS

Inspecting For Carpenter Ants

Carpenter Ants Control Methods

Pesticide Applications for Carpenter Ants    Carpenter Ant Baits

Mechanical Modifications   Baits   Preventive Treatments

In some areas of the country, carpenter ants (wood ants) cause more damage to structures than termites.  They are difficult insects to control and can cause extensive damage to wood members in a fairly short period of time.  Carpenter ants do not actually eat wood but excavate galleries within it to use as nesting sites.   Foraging activity can occur at any time of day but usually peaks at night.   When foraging inside houses, carpenter ants are attracted to sweets, meat, grease and fat.

A carpenter ant colony is usually formed by a queen who begins a nest in a piece of old buried wood or in a partially decayed tree or stump.  In mature infestations, there may be as many as ten satellite colonies linked to the parent colony by trails.  There is a frequent exchange of workers between these satellite colonies and the main nest.  Colonies normally do not produce winged reproductive forms until they are at least three to six years old with emergence of swarmers typically occurring from May through July.

The most common way in which homes become infested is through emigration of an existing colony.  Houses located near wooded areas or brush covered vacant lots are good candidates for infestation.  Carpenter ant colonies are inclined to move if they are disturbed, as often happens during construction.  Thus, new homes or those surrounding a new building lot present likely locations for attack.

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Inspecting For Carpenter Ants

Some Common Signs of Carpenter Ant Infestations:

• Frass, which is made up of wood shavings, bits of soil, dead ants and parts of insects.  This material is often piled up outside of nest openings and found in spider webs and window sills.
• Small windows or slit-like openings that carpenter ants cut into infested wood.   These windows are actually "garbage chutes" which are used to dispose of frass or unwanted materials.
• Swarmers are the winged reproductives that take flight in the spring.  Look for them trapped in spider webs, on window ledges or in light fixtures.
• Worker carpenter ants are active mostly at night, so you may not see any activity during normal working hours.  Even if you do, it does not mean that the nest is nearby.  Worker ants can travel up to the length of a football field booking food.
• Clicking or rustling sounds can sometimes be heard coming from carpenter ant nests.  If you identify a potential nest site, try tapping against it with a screwdriver.  You may hear a response -- the clicking of alarmed ants.
• Wood damaged by carpenter ants contains galleries that are very clean and smooth.