Question: My neighbor has an insect problem consisting of large black ants in his trees. They are eating out the trees, up and through the interior. As we inspected the trunk stumps, my neighbor showed me the black ants running in and out of holes. He told me the arbor people said that they would attack red oaks first, and then others.
Would you mind giving your expert opinion? Is it what he says? Is it spreadable? I have never heard of ants attacking large healthy looking hardwoods !
Answer: Those large black ants are called carpenter ants and seek out favorite food and nesting material created by wood decay. These ants are secondary insects, attracted to tree rot but not to healthy wood. Carpenter ants nest in trees with rotting, decayed wood or in soft center heartwood sections of trees. In no case are the ants harmful to the tree but can be annoying pests when nesting or foraging in or near residences.
Your neighbor's hardwoods have butt or heartwood rot and probably have had it for years. Not much can be done now but to keep the tree as healthy as possible. Trees tend to compartmentalize rotting sections with healthy wood and can live long even with considerable heartwood rot.
If you must treat for carpenter ants use a slow-acting insecticide that will kill the foraging ants over a period of time. Quick kill products only train them to avoid the treatment area.
Carpenter Ant - UGA Department of Entomology