Carpenter ant nests are very common inside trees, especially older trees that are hollow or have a significant amount of dead limbs and branches. The nests are usually in rotted, decayed wood, although some nests may extend into sound heartwood in the center of the tree.
Carpenter ants in trees are not directly harmful to the tree. Control is not essential for the tree's health, as the ants are only taking advantage of an existing situation of soft, weak wood in which to establish their colony. Stress, mechanical injury, environmental conditions, disease or other insects are responsible for killing limbs or sections of the trees in which the ants are able to nest. Once injury has occurred, wood decay can set in if moisture is present; it is the wood decay that gives the carpenter ants the opportunity to colonize the tree. Carpenter ants use knots, cracks, holes and old insect tunnels to gain access to these areas.
Control of carpenter ants inside trees is difficult but can be done as a way to reduce invasion of the ants into adjacent structures. It is also possible for ant colonies located inside trees to form satellite colonies inside a nearby home wall. Available controls are not likely to permanently rid a tree of carpenter ants so retreatment every year or so may be necessary. Dust insecticides (such as Sevin or rotenone) labeled for use on trees in the landscape are suggested for control. Apply the dust directly into the nest cavity.
Plugging or sealing tree cavities or treating tree wounds with wound dressings is not advised. Such treatments are unnecessary and will not eliminate nor prevent decay or carpenter ant activity.
This article originally appeared in the May 26, 1995 issue, p. 78.