Carpenter ants are the largest ants in Maryland, with winged reproductive forms reaching up to 3/4 inch long. They’re most active from spring through fall, and while they don’t eat wood like termites do, they excavate smooth galleries inside it to build their nests. That excavation can cause real structural damage over time, especially in homes with moisture problems. Here’s what Maryland homeowners need to know about identifying, preventing, and dealing with them.
What They Look Like
Maryland’s carpenter ants are typically black or dark brown, though some have reddish-brown midsections. Workers vary in size even within the same colony, ranging from about 1/4 inch to 1/2 inch. The winged males and queens that swarm in spring and early summer are the most noticeable, measuring up to 3/4 inch, making them the largest ants you’ll encounter in the state.
The easiest way to confirm you’re looking at a carpenter ant (and not a termite) is to check three features. Carpenter ants have elbowed antennae, a narrow pinched waist, and front wings that are noticeably longer than their hind wings. Termites, by contrast, have straight antennae, a body that’s the same width from head to tail, and two pairs of wings that are equal in length. This distinction matters because both species swarm around the same time of year in Maryland, and the treatment approaches are completely different.
When They’re Most Active
Carpenter ants typically enter Maryland homes during two seasonal windows: as temperatures warm in spring and again as they cool in fall. Spring and early summer bring the most visible activity, when winged queens and males emerge from mature colonies to mate and establish new nests. If you see large winged ants inside your home during this period, it strongly suggests an established colony is already nesting somewhere in the structure.
During summer, worker ants forage mostly at night, following trails along foundations, wires, pipes, and tree branches that contact the house. You might spot a line of large black ants marching across your kitchen floor after dark. In fall, ants that have been nesting in outdoor trees or woodpiles sometimes push indoors seeking warmth and shelter for winter.
Signs of an Infestation
The most straightforward indicator is regularly seeing worker ants inside your home, particularly during months when they wouldn’t normally be foraging outdoors. A few ants wandering through in spring doesn’t necessarily mean a colony is inside your walls. But consistent sightings, especially in winter, point to an indoor nest.
More definitive signs include small piles of wood shavings near baseboards, window frames, or door frames. These shavings look like pencil sharpener scraps, mixed with bits of dead insects and other debris that the ants push out of their nests through small “window holes” in the wood surface. The wood itself may look fine on the outside, but the galleries inside are smooth and polished, distinct from the rough, mud-packed tunnels that termites create.
In a severe infestation, you can sometimes hear faint rustling sounds inside walls or woodwork, particularly at night when the ants are most active. And if large winged ants emerge from ceilings, walls, or other hidden spaces inside your home, an established colony is almost certainly present.
Where They Nest
Carpenter ants rarely nest in dry, sound wood. They strongly prefer wood that’s already been softened by moisture, decay, or damage from other insects. In Maryland homes, that typically means areas around leaky roofs, poorly sealed windows, bathroom walls, and anywhere condensation accumulates. Common nesting sites include wall voids, hollow doors, window frames, foam insulation panels, and structural lumber in attics or crawl spaces.
Outdoors, they nest in dead trees, stumps, rotting fence posts, and landscape timbers. A colony often maintains a main nest outdoors and one or more satellite colonies inside a nearby home. The satellite colonies can exist without a queen and contain workers, older larvae, and pupae. This is why killing the ants you see inside doesn’t solve the problem: the main colony keeps sending reinforcements.
How They Get Inside
Carpenter ants exploit any gap in a home’s exterior. Common entry points include attic vents, foundation cracks, gaps around electrical wires, plumbing penetrations, and telephone lines. Tree branches and shrubs that touch the house act as highways, giving ants a direct bridge from outdoor colonies to your siding or roof. Firewood stacked against the house is another classic pathway.
Prevention That Actually Works
Because carpenter ants target moisture-damaged wood, the single most effective prevention strategy is eliminating moisture problems. Fix leaky faucets, repair roof leaks promptly, ensure gutters drain away from the foundation, and ventilate crawl spaces and attics properly. Replace any wood that’s already begun to rot or soften, especially around windows, doors, and sill plates.
Beyond moisture control, reduce the connections between your yard and your home. Trim tree branches and shrubs so they don’t contact the house. Store firewood at least 20 feet from the foundation and elevate it off the ground. Remove dead stumps and rotting wood from your property when feasible. Seal cracks in the foundation and gaps around utility penetrations with caulk or expanding foam.
Getting Rid of an Active Colony
Effective treatment depends on finding the nest, or ideally, all nests. Following the trails of foraging ants at night with a flashlight can lead you to entry points and nest locations. Piles of wood shavings mark nest openings.
For nests inside wall voids, dust-based insecticides are the appropriate choice. Liquid sprays should never be used inside walls because the moisture can damage insulation, drywall, and electrical wiring. Dust products based on boric acid, silica gel, or diatomaceous earth can be injected into the wall through the ants’ existing entry holes or through small drilled access points using a hand duster with a narrow tip. These dusts coat the ants as they move through the galleries and are carried back to other colony members.
Over-the-counter liquid baits, like those containing boric acid, can work for some ant species but tend to be less reliable for carpenter ants because of their varied diet. They may reduce visible foraging but often fail to eliminate the colony. Non-repellent liquid insecticides that transfer between ants through contact are more effective at reaching the queen and killing the colony, but many of these products are only available to licensed pest management professionals.
Professional Treatment Costs in Maryland
Specialized carpenter ant treatment in Maryland typically costs between $250 and $700 or more, depending on the severity and accessibility of the infestation. That price range covers structural inspection, wall void treatments, targeted dust applications, and perimeter spraying. Carpenter ant jobs land on the higher end of ant extermination costs because the ants nest inside structural wood, often requiring drilling into walls and treating multiple colony sites. A straightforward case with one accessible satellite colony will be closer to $250, while a multi-colony infestation in hard-to-reach wall voids or attic framing can push well past $700.
Many pest control companies in Maryland offer follow-up visits as part of the initial treatment package, since eliminating all satellite colonies on the first attempt isn’t always possible. Ask whether retreatment is included before signing a contract.
Carpenter Ants vs. Termites: Damage Comparison
Both insects damage wood, but in different ways and at different speeds. Termites actually consume wood as food and can cause extensive hidden damage relatively quickly. Carpenter ants only remove wood to create nesting space, pushing the shavings out rather than eating them. Their damage accumulates more slowly, often over years. That said, a large carpenter ant colony left unchecked in a structural beam can compromise its integrity over time, particularly when the wood was already weakened by moisture.
Maryland is home to eastern subterranean termites, which swarm around the same spring window as carpenter ants. If you find winged insects inside your home, the antenna and waist checks described above will tell you which pest you’re dealing with. The distinction is worth getting right, since termite treatment involves very different methods and typically costs significantly more.