The carpenter ant is one of the larger ant species, typically ranging from 1/4th to 1/2 inch long. They are black or dark brown and have a segmented body with a large thorax. Their antennae are also segmented and they have two pairs of wings (although many times they will lose one or both wings).
The best way to prevent carpenter ants is to seal all cracks and openings in your foundation and exterior walls. Make sure there is no wood debris or other potential food sources near your home. If you see an ant trail, use a commercial ant killer or bait to eliminate the colony. Finally, keep your home and property well-maintained to discourage them from nesting there in the first place.