Habitat: Carpenter ants hollow out spaces in wood to use as nests. Most species nest first in decayed wood and then enlarge the nest into sound wood. Indoors: nests are in wood (perhaps softened by fungus rot), insulation, wall voids. Outdoors: nests are in old firewood, rotting fence posts, stumps, dead portions of living trees, under stones and logs. A colony has a main nest connected to satellite nests by a cleared trail about 1/4 inch wide.
Biology: A mature colony of western carpenter ants may have 10,000-20,000 workers, or up to 100,000. Swarmers aren’t produced until the colony matures. In the West, swarmers may appear between February and June. There is usually just one functional, wingless queen per colony. Development from egg to adult takes at least 60 days.
- Look for piles of sawdust-like shavings, sometimes with bits of insulation and insect parts.
- Listen for rustling sounds from within the walls. (A listening device is useful.)
- Watch for foraging trails outside, especially between 10 am and 2 pm.
- Be alert to the emergence of swarmers.
- With a tool gently tap exposed wood and rafters, listening for a hollow sound which might indicate a nest cavity. A knife blade will easily sink into the wood if a nest is present.
- Check attics, basements, and crawl spaces. Check wires and pipes. Locate high moisture areas. (A moisture meter can be useful.)
- Preventive measures include barrier treatment, pruning of plants near buildings, caulking of gaps, and treating the lowest 3-6 ft. of tree trunks and utility poles.
- The parent colony must be located and destroyed by treating directly with an appropriate registered pesticide. This may require drilling into wood or wall voids.