(fire ants)

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Black Carpenter Ant

Inspecting For Carpenter Ants

Carpenter Ants Control Methods

Pesticide Applications for Carpenter Ants

Mechanical Modifications   Baits   Preventive Treatments

In some areas of the country, carpenter 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.

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.

The first sign of a carpenter ant infestation is usually the sighting of numerous workers throughout the home.  However, the presence of workers alone is not conclusive evidence that a colony is established within a structure.  Carpenter ant workers tend to roam far and wide looking for food, and some transient workers are sure to enter any home located in a wooded area.  Signs of an active infestation include the presence of fibrous sawdust beneath slit-like openings in wood members and faint, rustling noises in walls and woodwork.  A positive indication that an active, mature infestation is present is the emergence of large winged ants from walls, ceilings, or crawl spaces.

Carpenter ant galleries in wood have smooth surfaces and can be differentiated from subterranean termite damage by the absence of "mud" in the galleries.  Ants normally excavate wood that has been softened by decay or other insects, however, they will tunnel into sound wood when conditions are favorable.   Nests and galleries may be located a considerable distance from the point or points of entry.  In addition to structural lumber, sites such as hollow-core doors, window headers, wall voids, and foam panels are particularly attractive to carpenter ants.

Carpenter ants often enter homes through openings such as foundation or attic vents, cracks, plumbing holes, entrances for telephone and electric wires, etc.  One thing to look for during an inspection are tree branches that may be just above or in contact with the roof.  Firewood piles are prime nesting sites and should be treated with an appropriately labeled pesticide such as Advance Carpenter Ant Bait, Suspend SC or Cyper WP.

Carpenter Ant Control Methods

Mechanical Modifications           Pesticide Applications

Mechanical Modifications

The first step in carpenter ant control should always include mechanical modifications to the structure and environment.  The object is to reduce the avenues available for carpenter ants to enter a home or structure, as well as removing possible food and water sources.

  • If any tree limbs are in contact with the roof, cut them back.   Carpenter ants can easily drop to a structure from tree limbs as high as five feet above the roof.

  • Move firewood away from the house.  Keep firewood elevated so as not to have direct contact with the soil.  This will protect it from other wood destroying organisms (termites, decay, fungus) besides carpenter ants.

  • Seal cracks along foundations, siding, windows and doors with caulk and install fine mesh screens over crawl space and attic vents.

  • Insects need water in addition to food and eliminating sources of water will make an area less attractive to carpenter ants.  If necessary, fix plumbing leaks, reroute air conditioner drains and make sure sprinkler heads are properly adjusted.

Pesticide Applications for Carpenter Ants

There are basically four methods of pesticide application used for controlling active infestations of carpenter ants:  exterior perimeter treatments, interior void treatments, treating the infested wood and baiting.

Perimeter Insecticide Treatments

The most commonly used method for controlling carpenter ants is treating the perimeter of a home with a dust or spray.  There are several products available for this type of application, but Cyper WP, D-Fense SC are most popular.  When used in accordance with their labels they work well.  However, these treatments do not keep ants from entering a home from overhead trees and power lines.  Also, as a stand alone treatment, they rarely eliminate ants inside voids and walls.

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Interior Void Treatments

Crusader Duster   Delta Dust   Drione Dust  Foam

The treatment of interior wall voids has become more popular with the availability of insecticide dusts and the introduction of foaming applications.  The efficacy of  dusts depend on ants ignoring their presence and walking through them, contaminating the ants' bodies in the process.  Ants then ingest the insecticide while grooming.  If dusts are not applied properly, ants and other insects simply detour around the insecticide.  To apply dusts properly, an electric duster or bellows duster (such as the Crusader Duster) must be used.  You need to use either Drione Dust or Delta Dust for carpenter ant infestations of interior wall voids.  Drione Dust works well in a dry environment, but Delta Dust is the best where there is any sign of moisture.  Delta Dust is a synthetic pyrethroid insecticide dust that is water proof.

One limitation of this control method is that the dust must be placed directly onto the pathway used by the ants.  If, for example, the dust is placed on the floor plate and the ants are using an electrical conduit located three inches above the plate as their pathway, control will not be attained.  This means simply that dust is an excellent tool, but should be used along with other control methods, not as a "stand alone" carpenter ant eliminator.

Another problem with using dusts is their sensitivity to high moisture conditions.  Dusts have a tendency to cake or crust when they get damp.   This makes them ineffective since ants can then walk across them without picking any up on their bodies.  Only Delta Dust is water proof.

Spot Treatments of Infested Wood

Spot treating infested wood with Bora-Care will quickly eliminate a localized carpenter ant infestation.  Whenever practical, inject Bora-Care directly into the carpenter ant galleries.  However, it is important to treat an entire infested area in order to reduce the possibility of colony relocation.  A frequent problem encountered with carpenter ants is the fragmentation of a colony when subjected to a pesticide.  Bora-Care, like many other pesticides, is repellent to carpenter ants and may cause them to avoid treated areas and seek out untreated wood.  The best treatment method consists of not only treating the infested area, but also treating all wood susceptible to attack.  This would include an entire crawl space, wall or attic showing any signs of damage.  All bare wood should be sprayed to the point of wetness.  Confined areas can be treated using a foaming device or fogging device (foaming is best) but heavily infested wood should be directly sprayed either before or after fogging or foaming.  

Treating Infested Foam Panels

Carpenter ants will occasionally infest foam insulation panels around foundations and under stucco and other types of siding.  Carpenter ant infestations in foam may be treated by spraying the infested area, if accessible, or by drilling and injecting diluted Bora-Care directly into ant galleries.  To foam inside wall voids, hollow block or other such areas, use Termitafoam.  This product turns your insecticide into a shaving cream type solution which helps disperse your pesticides into those hard to reach areas.


The newest and most efficient method of controlling carpenter ants is by using baits.  Baits work by decreasing the population of carpenter ants in an area, thus reducing their potential for entering a structure.  Advance Carpenter Ant Bait, Niban Granular Bait and Niban-FG Fine Granular Bait are carpenter ant baits which can be used for both interior and exterior applications.  Maxforce Carpenter Ant Bait Gel is the fastest for indoor ant colonies.

Note: One of the quickest ways to destroy the effectiveness of any bait is to contaminate it with another pesticide.  Never treat the same area with both a spray and a bait at the same time.  If you must use a pesticide spray, wait at least two weeks after application before beginning your baiting program.  And never use the same containers, measuring cups or dusters for both baits and contact pesticides.  A little bit of pesticide residue can contaminate a lot of bait!

Exterior Baiting

A primary objective in an exterior baiting program is to place a band of bait between the satellite colonies in the structure and the main nest.  Since there is a continual exchange of workers between satellite colonies and the main nest, you want to give worker ants an opportunity to pick up the bait on their way to and from nesting sites.  Since the main nest is frequently in an old log stump within a 300 foot radius of the home, it is important to locate and treat it with the bait.  Although following ants and their trails to the main nest can be a tedious task, especially at night, it is well worth the effort.  Elimination of the main nest will substantially reduce the risk of re-infestation.

A two to four foot band of Niban Granular Bait or Advance Carpenter Ant Bait should be applied around the perimeter of the structure as well as around the base of all trees, stumps, firewood piles and other locations where carpenter ants may nest.  Niban Granular Bait should also be applied along ant trails and other areas where ant activity has been noted.

Unlike other carpenter ant baits, Niban Granular Bait will not degrade from exposure to heat or sunlight and studies have shown that Niban will remain effective through about two inches of rainfall.  Re-application of Niban Granular Bait should be made periodically during intervals of very wet weather.  Advance Carpenter Ant Bait is the newest bait for carpenter ants that is getting great reviews from pest control operators around the nation.

Interior Baiting

Whenever possible, exterior baiting should be combined with an interior baiting program.  This will speed the eradication process and provide residual bait in order to prevent a re-infestation.  However, you must use a long-lasting bait like Niban-FG Fine Granular Bait  or Advance Carpenter Ant Bait which will remain effective for months rather than days or weeks.

Preventive Treatments

As previously stated, new construction is particularly susceptible to carpenter ant attack.  Un-infested wood properly treated with Bora-Care will be protected from carpenter ant attack.  Exterior wood surfaces exposed to rain or snow which have been treated with Bora-Care should also be coated with a water resistant finish such as paint or stain.  Interior Bora-Care treated wood surfaces do not need to be coated.

During construction, the application of Niban-FG Fine Granular Bait in wall voids and other confined spaces will help prevent carpenter ant infestations.   Re-application of these baits on a periodic basis will significantly reduce the likelihood of carpenter ants establishing a satellite colony within a structure.


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