Utah Pests News Spring 2008

click here for pdf version

Got Frass? Carpenter Ants May be the Culprit

  Side view of Camponotus modoc.

Carpenter ants in the genus Camponotus (Hymenoptera: Formicidae) are considered some of the most serious pests to wood structures in the United States and worldwide.  With 50 species of carpenter ants found in the United States and Canada, some are likely to be near your home.


As with termites and some insects in the bee, wasp, and ant order (Hymenoptera), carpenter ants exhibit sociality.  For ants, sociality includes having a queen, multiple generations of worker ants, male reproductive ants, and sharing of responsibilities in the colony.  Most importantly, the ant social system is dependant upon food sharing (trophallaxis), and the transfer of nutrients through bodily secretions.  Carpenter ants have a range of worker sizes from big (majors) to small (minors) and sizes in between (medias), and have multiple queens.  Typical carpenter ant colonies can contain from 3,000 to 100,000 workers.

Western carpenter ant (Camponotus modoc) head view.  

Like butterflies and moths, ants have a complete life cycle consisting of an egg, numerous larval stages and a pupal stage that develops into an adult.  In Utah, homeowners are most likely to see carpenter ants swarming in spring when winged males and queens congregate to mate.  Often, swarms occur in the late afternoon and early evening on sunny, warm days preceded by rain.  If the swarm occurs inside the house, then it is likely that a nest is located inside.  Winged ants are often mistaken for termites.  If suspected ants or termites are on your property, multiple samples should be collected and submitted to the Utah Plant Pest Diagnostic Lab for proper identification.

Carpenter ants do not need to swarm to form new colonies, but can create new colonies by budding.  This process involves a number of worker ants leaving an established colony with at least one queen and starting a new colony.  This allows carpenter ants to be highly mobile and start new colonies when established ones are disturbed.  Because of this adaptation queens and brood (eggs and larvae) must be eliminated when spray treatments are used.

Another important nesting habit of carpenter ants is the satellite colony.  As the name suggests, these are smaller nests that are separate from the main colony and contain all ant castes.  For example the main nest may be in the back yard, while a satellite of that nest may be located in a wall void.  When treating carpenter ants, the main nest along with the satellites must eradicated.  Remember that carpenter ants usually nest at the bottom of wall voids, above doors in the wall void, in large structural beams, or outside in the ground or in trees.

          Carpenter ant (Camponotus) species occurring in Utah  
Scientific Name Major Structural Pests
C. vicinus yes
C. herculeanus yes
C. laevigatus no
C. modoc yes
C. noveboracensis no
C. essigi yes
C. hyatti no
C. nearcticus yes
C. semitestaceus no
C. sayi no
All aspects of carpenter ants are not negative, however, as these organisms play vital roles in maintaining a healthy environment.  Carpenter ants are voracious predators in the forest ecosystem.  The often consume large prey consisting of stink bugs, leaf beetles, spittle bugs, and scavenge on dead insects. Ants help speed the decomposition of wood by perforating wood cells allowing moisture and other wood decaying organisms to invade.  Ants are also a food source for many bird species.


Carpenter ants may be located from the dust (frass) they deposit when chewing through wood.  Piles of frass can be found below carpenter ant nests or tunnels.  Another indication of nest presence is seeing ants in the house.  Nests can be located by observing ant activity and following lines of ants (ant trails) back to their source.  Often, ant trails are located beneath baseboards and under carpets and aren’t obvious.  Difficulty tracking ants occurs when trails enter wall voids, usually along plumbing or electrical pathways.  Ant nests can be difficult to locate, and may occur outside the house, even in your neighbor’s yard. If ants are found, it is best to call a professional pest inspector so that the main, and satellite nests are located before treatment. 

The Field Guide for the Management of Structure-Infesting Ants has a list of all areas where nests may be located:

• Firewood
• Landscape timbers
• Tree stumps
• Dead tree limbs
• Fence posts and rails
• Under hot tubs
• Decking materials
• Voids above porches
• Voids above bay windows
• Under attic insulation
• Roofing boards
• Wall voids
• Tree holes
• Hollow wooden doors
• Hollow curtain rods
• Hollow shower rods
• Hollow ceiling beams
• Under bathtubs
• Sill plates and floor joists
• Styrofoam sheeting
• Attic eaves
• Under insulation in crawl spaces

Once nests are located there are various treatment options depending on their location:

• Carpenter ants located inside structural wood are treated by drilling into the nest and injecting insecticidal dust or aerosol formulations.

• For ants nests located in firewood, infested wood is removed from the property.

• If ants are located in insulation, the insulation may need to be removed before insecticide treatment, otherwise, aerosol formulations are used.

• When ant colonies occur outside the house, insecticidal barrier treatments may be placed around the perimeter of the foundation.  If mounds are found outdoors, then a complete insecticidal soil drench of the mound can provide effective control.

Ant baits may only be partially effective at controlling carpenter ants, and should be used in conjunction with other methods for increased control.  Spraying worker ants outside the nests will not get rid of them; the nest must be treated by a professional.

While insecticidal treatments might provide a temporary solution, treating the conditions favorable to carpenter ants is paramount to long-term control.  Carpenter ants prefer wood with high moisture content, especially when the wood is infested with mold/fungi.  Some suggestions on reducing moisture in ant-prone areas are to increase ventilation in crawl spaces, basements and attics, use a poly-sheet to cover 75 to 80% of exposed soil in crawl spaces, fix leaky plumbing fixtures, use a dehumidifier in the house, make sure there are no leaks in the foundation, roof, or any part of the house, and in extreme cases, a sump pump may be needed in areas where there is a high water table.

Other cultural controls that are critical include sealing all cracks in the walls and roof, using weather stripping on the bottoms of windows and doors, trim trees and shrubs so that they are not in contact with the house, and creating seals where cable, electrical, or plumbing hardware enter the house.  Since carpenter ants tend various insects (e.g. aphids) for their sugar-rich honeydew excretions, controlling those organisms will reduce potential food sources.  Vacuuming and cleaning regularly will help keep ants from coming into the house looking for food and will reduce the temptation to colonize in wall voids.

Carpenter ants are major players in ecological systems throughout the world and should only be viewed negative when they are causing damage to a house, business, etc.  If ants, or signs of ants are noticed on the property, samples should be collected and identified; many household ants are not carpenter ants.  A professional pest inspector should be contracted to locate ant nests and implement the proper control procedures.  In addition to insecticide use, long-term control must include cultural methods which can usually be done by the homeowner.


-Ryan Davis, Arthropod Diagnostician