Isee these big black ants inhabiting a tree in my yard. What kind of ants are they, and what can I do to kill them?
A: Those big black ants are carpenter ants. Because I get some calls on occasion about them, I will explain a little about their biology so that you and others will understand the steps to take to get rid of them.
Carpenter ants get their name because of their habit of chewing wood to create nest sites. They do not eat wood, like termites, but excavate it with their strong, serrated jaws to create random galleries where they nest.
Carpenter ants are also a nuisance because of their abundance and their large size.
Carpenter ants are the largest of the pest ants found in Georgia and South Carolina.
They are most active at night, when it is not uncommon to see ten- to twentyfold more than would be seen during daylight hours.
Ants emerge about 15 minutes after sundown and leave the nest in large numbers in search of food, traveling up to hundreds of feet from the nest on semipermanent trails. In the evening, ants can be seen using these trails as they emerge from and return to their nest. Colonies might even use the same trail in different years.
Carpenter ants can establish nest sites inside or outside the home.
Places where carpenter ants have been found nesting inside are moisture-damaged wood around chimneys and skylights, under bathtubs, in wall voids beneath window sills, inside hollow doors and door frames, under fiberglass insulation in crawlspaces, in wood porch supports and columns, under siding and wood shingles and in moisture damaged eves.
In general, wood suffering from moisture damage will attract and be used by carpenter ants as nest sites because damp wood is easier to chew than sound, dry wood. Damp wood combined with warm temperatures also promotes the survival, growth and reproduction of carpenter ant colonies.
Outdoors, nests are most commonly found in hardwood trees containing holes. Most large hardwood trees contain a tree hole or other imperfection where ants might nest.
In tree holes, ants find an environment that is ecologically stable (consistent humidity and temperature) and protected from adverse environmental conditions and natural enemies. There they chew dead wood to
create galleries for nest sites.
The key to eliminating carpenter ant infestations is to find the nest and treat it with an insecticide. Inspect all locations I listed above for indoor and outdoor nest sites.
To find a nest site indoors, follow a few foraging ants to learn where they might be nesting.
Tap the area suspected of harboring the nest. This excites the ants, allowing you to detect their presence by hearing their raucous movement.
Look for small piles of wood debris resembling sawdust that ants drop from the nest during excavation of the wood. Close examination of the debris might reveal parts of dead carpenter ants and the uneaten pieces of prey insects brought to the nest for food.
Carpenter ants found in the home often can be found nesting outdoors in trees. To find outdoor nest sites, inspect each large tree (greater than 6 inches in diameter) beginning 15 to 20 minutes after sundown by walking around it while shining the flashlight up and down the trunk. If a nest is present, ants will be seen on the trunk as they leave the nest and return with food.
Because carpenter ants use permanent trails, use a flashlight to find ants on the trail and follow them as
they move to and from their nest.
Finding just part of the trail can be a tremendous help in finding the nest. After locating several points along a trail, a directional pattern will emerge and often lead directly to the nest.
Because carpenter ants must excavate wood to expand their galleries, it is common to find piles of sawdust at the base of a tree where they nest. Galleries are created by biting off small pieces of wood and disposing of it outside.
The small bits of wood often pile up at the base of a tree and take on the appearance of sawdust.
Any insecticide you use will be effective in killing carpenter ants. The key is getting it to the nest.
REACH SID MULLIS, THE DIRECTOR OF THE UNIVERSITY OF GEORGIA EXTENSION SERVICE OFFICE FOR RICHMOND COUNTY, AT (706) 821-2349 OR SMULLIS@UGA.EDU.