Carpenter ants are quite large, from 1/4 o 3/8" long; dark brown to black, but some may have a red or yellowish coloration. The usual carpenter ant is large and black.

Click here for a picture of carpenter damage

DIET:

They eat a variety of plant and animal foods and sweets. These ants will also feed on other insects. They do not digest wood.

BIOLOGY:

Being social insects, they have different forms of "castes" in their colonies. Mature colonies have winged a nd wingless queens, winged males, two sizes of wingless workers, and immature stages (eggs, larvae and pupae).

They do swarm and mate during the springtime.
Swarming generally occurs after three-six years, when a colony contains 3,000 or more ants.
A single queen starts a new colony.
Damage can occur before a homeowner is aware of the presence of carpenter ants, because it takes a while to build up the colony in population before you may take notice of foraging ants or swarmers.
Carpenter ant colonies inside homes may release swarms indoors.
Carpenter ants in the house during the winter months or winged carpenter ants indoors at any time of year is a sign that they have a nest somewhere in the house.
If it is just a few workers , seen during the summer months, more likely they are simply foraging from the outside; entering and exiting.

A carpenter ant colony may contain a main nest and one or more "satellite" nests.
The main nest contain the queen, eggs and larvae, and workers.
Ants in these "satellite" nests are the ones that normally do structural damage to homes.

During the winter months, the ones outside are inactive.
Indoor nest can remain active, but at a reduced rate.

HABITS:

They are nocturnal. There activity peaks between 8:00 p.m. and 4 a.m.Their ideal temperature for habitation is between 71 degrees to 74 degrees F. It would be advantageous to inspect at these times and temperature conditions.

They usually nest outside in moist wood or partially decayed wood in that they prefer the "softened wood" to hollow out their nests called "galleries".
These galleries are quite clean and have a sandpaper appearance.
(Termite galleries are rough looking in comparison.)
Wood which has been damaged by carpenter ants contains no mud-like material, as is the case with termites.
Nests are especially common in such places as moist, hollow spaces, like the wall void behind dishwashers.
Nests are usually found in areas where water leakage could occur, around bathtubs, sinks, roof leaks, poorly flashed chimneys,
or poorly sealed windows or door frames.
Outdoor nest can occur in stumps, hollow logs, fence posts or in dead portions of standing trees, however cracks and crevices may be used to start nests in sound wood.

They may establish nests in a number of different locations.
It is important to understand than you can have both inside and outside nests.
They construct two different kinds of nests: parent colonies which, when mature, contain an egg-laying queen, brood and 2000 or more worker ants, and satellite colonies which may have large numbers of worker ants, but no queen, eggs or larvae.
The carpenter ants inside a home may have originated from the parent nests located outdoors in a tree stump, timber or woodpile for example, or from one or more satellite nests hidden behind a wall in the kitchen or bathroom, or perhaps from wood dampened by a roof leak in the attic.
Although large colonies can cause structural damage, the damage is not normally as serious as termite damage.
 

HOW TO DETECT GALLERIES:

Many times you can see "sawdust" near these carpenter ant galleries.
This "sawdust" or "frass", are shredded fragments of wood that has been ejected from the galleries.
This is a good indication that a nest is nearby.
But sometimes this evidence is not seen, taking a screwdriver, probing the wood may reveal the excavated galleries.
Also, you could take the blunt end of the screwdriver to tap along baseboards and other wood surfaces listening for the hollow sound of damaged wood.
If a nest is nearby, many times the carpenter ants will respond by making a "rustling" sound within the nest, similar to crinkling of cellophane.

FORAGING CARPENTER ANTS FROM THE OUTSIDE:

Many times the ones that you see inside your home are simply foraging for food, you won't see large numbers typically.
Foraging ants can travel 100 yards from nest to food and can be simply found wandering throughout your house.
However there can be indoor nest found in hollow doors, window sills, behind baseboards, or other natural hollow areas.
Their damage usually indicates water damage and wood decay.