Carpenter ants are one of the most common household insect pests in Virginia. These medium to large black ants usually enter houses during spring and early summer. While these ants do not form distinct trails, large numbers of ants forage for good scraps in kitchens and bathrooms and create a nuisance by their presence. The discovery of carpenter ants in the house frequently causes homeowners concern – there is a fear they can damage structural wood! Let’s review the biology and habits of carpenter ants.
* Wood-infesting habits: Carpenter ants infest moisture damaged wood. They do not actually eat wood, as termites and some beetles do, but excavate galleries in moist wood for rearing the young – the nest. Carpenter ants are quite skilled in locating wood that is acceptable for nest construction. They can enter a house at the roof line and locate a few feet of a 2-inch by 4-inch that has been exposed to moisture from faulty flashing around a chimney, or find wet wood behind a bathroom shower. The mandibles, or mouth parts, of carpenter ants can remove wood that has been wet and attacked by fungi, but their mandibles cannot easily tear off sound wood.
* Seasonal activity: Carpenter ants can be found in houses and other structures at two times during the year – late winter and late spring.
* Late winter: Some households experience carpenter ants in the kitchen and bath areas during the warm days of January and February. When this occurs, there is an excellent possibility that there is a colony of carpenter ants in the house – somewhere! It may take careful examination of all potential nest areas, where wood is, or can be, exposed to water, to locate a carpenter ant nest.
* Late spring: Households that experience these large black ants during late spring and early summer, probably do not have a nest in the house, but have one outside – perhaps in the wood pile, an old tree, or in the neighbor’s woodpile! Carpenter ants forage for food over a wide area and may include houses and other structures. These ants will eat a variety of material and usually eat on their own. The primary food for carpenter ants is other insects, especially aphids. Carpenter ants take some food back to the nest, but in general the workers forage by themselves. Although they do make trails while foraging for food, the trails are not easily seen and ants certainly do wander from the trails!
The reason these ants are most common in the spring and less so in summer and fall is their foraging habits. Carpenter ants shift their foraging activity, looking for aphids and other insects to feed on, late and later in the day throughout the summer. By August, they are foraging during the late afternoon and evening hours – and go unnoticed.
* What to do! Carpenter ants do not cause the same amount of damage as termites. The colony is limited in size, limited by the moisture damaged wood, and carpenter ants don’t eat the wood. Control of these insects should begin with locating the nest – not any easy task! What to do?
* First! When do you see large black ants in the house? Late spring/summer – probably need to worry. If in late winter, perhaps there is a nest in the house.
* Next, examine the house for all possible locations of moisture-damaged wood. Carefully inspect those areas. Look for ants, wood shavings, not powdered sawdust, but coarse pieces – all about the same size.
* If you can locate the nest, or any part of it, you can begin control. Removing the damaged wood will be the best control, but you can also apply common insecticide, aerosol or mixed in a sprayer.
* Applying insecticide to door thresholds and around other openings to the house, such as pipes and wires, can help reduce the number of carpenter ants that may just wander in looking for food.
