A black ant with a red or reddish-brown abdomen is most likely a bicolored carpenter ant, specifically Camponotus chromaiodes, sometimes called the red carpenter ant. Field ants in the Formica genus can also show this color pattern. Both are common across the eastern and central United States, and telling them apart matters because carpenter ants can nest in the wood of your home.
Red Carpenter Ant: The Most Common Match
Camponotus chromaiodes gets its nickname from the reddish coloration on the middle body segment, the base of the abdomen, and the legs, while the head and most of the abdomen are black to dark brown. Workers range from about 6 to 14 mm long (roughly a quarter to over half an inch), making them noticeably large compared to most household ants. Queens can reach nearly 16 mm. The coloring is variable even within a single colony, so some individuals look almost entirely black while others show prominent red-brown patches.
One useful detail: red carpenter ant workers have fine golden hairs lying flat against the abdomen. These hairs overlap the edges of each abdominal segment and can give the rear end a faintly shimmery look under good light. If you can get a close look, you’ll also notice a single bump (called a node) between the middle body segment and the abdomen, and a smoothly rounded upper profile on the midsection. Both are hallmarks of carpenter ants.
Field Ants: The Easy Mix-Up
Field ants (Formica species) are the insects most often confused with carpenter ants because they overlap in size, color, and habitat. The Allegheny mound ant, for example, has a rust-red head and midsection with a blackish-brown abdomen and legs. Other Formica species come in brown, black, red, or various combinations.
The simplest way to separate the two groups is body shape. Field ant workers have an uneven, almost notched upper profile on their midsection when viewed from the side, while carpenter ant workers have a smooth, evenly rounded curve. Field ants also tend to be smaller, topping out around a quarter inch, and they have three tiny simple eyes (ocelli) on the top of the head that carpenter ants lack. If the ant you’re looking at is bigger than a quarter inch and has a smooth, arched back, it’s almost certainly a carpenter ant.
Where These Ants Live
Carpenter ants naturally nest in dead tree branches, rotting logs, and stumps. Their main colony is usually outdoors, but they establish satellite nests in spots where wood stays damp. Inside a home, that means areas around leaking chimney flashing, skylights, bathtubs, windowsills, doorframes, porch supports, and flat roofs. Poorly ventilated attics and crawlspaces with high humidity are especially attractive. Southern carpenter ant species tend to move into existing voids and cavities rather than chewing through solid wood the way their northern relatives sometimes do.
Field ants, by contrast, build their colonies in the ground, often in open yards, garden edges, or at the base of trees. They rarely come indoors. If you’re finding bicolored ants inside your house, carpenter ants are the more likely culprit.
Do They Bite?
Carpenter ants can bite if they feel threatened. They grab the skin with their jaws and release formic acid into the wound, which causes a sharp, burning sensation. They don’t have stingers like fire ants, so there’s no venom injection or pus-filled blisters. The bite is briefly painful but typically resolves on its own without treatment. Some people are allergic to formic acid and may develop a more pronounced skin reaction, but serious allergic responses to carpenter ant bites are uncommon.
Structural Damage Risk
Carpenter ants hollow out wood to create nesting galleries, but they don’t eat it. You’ll sometimes find small piles of sawdust-like shavings (called frass) near baseboards, windowsills, or door frames. This debris is a strong sign that a colony is excavating nearby wood. Large, established colonies can cause real damage over time, though most experts describe them as more of a nuisance than a serious structural threat. The bigger concern is what their presence signals: because carpenter ants prefer moist or decaying wood, an indoor colony usually points to an underlying moisture problem like a roof leak, plumbing issue, or poor ventilation.
Keeping Them Out
Prevention starts with moisture control. Fix leaky roofs, windows, doorframes, and plumbing. Make sure attics and crawlspaces have adequate ventilation. Paint or seal exposed wood before it gets wet, and replace any wood that’s already rotted or water-damaged. Trim tree branches and shrubs so nothing touches the exterior walls of your house, since ants use these as bridges.
Outdoors, remove dead stumps and keep firewood stored off the ground on a concrete pad, well away from the house. The longer a wood pile sits undisturbed, the more attractive it becomes. Seal openings in living trees, too, since hollow cavities are prime nesting real estate.
Dealing With an Infestation
Effective control means finding and treating the main colony and any satellite nests. Follow the trail of foraging ants, especially at night when carpenter ants are most active, and look for frass piles near walls or baseboards to locate nest entrances. Because carpenter ants eat a wide variety of foods, sugar- or protein-based baits that work well on other ant species are often unreliable for carpenter ants.
For nests inside wall voids, dust-based insecticide products applied directly into the cavity are the standard approach. Liquid insecticides should not be used inside walls because the water can damage insulation, drywall, and electrical wiring. Non-repellent formulations tend to work best: ants walk through the product without detecting it and carry it back into the colony, spreading it to nestmates before it takes effect. If you can’t locate the colony or the infestation is extensive, a pest control professional can use specialized equipment to track nest locations and apply treatments precisely where they’re needed.