Carpenter ants enter a tree through an existing wound and hollow out dead areas in the tree rather than eating live wood. So the ants are indicating that there is another problem going on with your tree that is creating the dead tissue and you should consult a certified arborist to examine the tree. It is unusual for the ants themselves to weaken the tree though you may still wish to get rid of them to keep them out of your house. The arborist should be able to tell you how to treat them and what products are licensed for use in your state.

You can find a certified arborist who works in your area through the International Society of Arboriculture arborist referral service.

Courtesy of NYBG Plant Information Sevice