Q: Some of my trees seem to be infested with carpenter ants. Are they harming the trees, and, if so, is there a way to get rid of them?

—Walter Fischbach, Perry Hall, MD

A: Roger Cook replies: A few ants in a tree are not a big concern, but an infestation of these critters can remove enough wood to weaken a major limb or the entire tree. And if an ­infested tree is close to the house, there's a chance the ants-or the tree!-will end up indoors.

To find out just how severe the damage is, hire a certified arborist to evaluate your trees using a Resistograph, a tool that measures how much the wood resists being penetrated by a drilling needle. This needle is so small that it doesn't harm the tree. The arborist can then tell you if the problem warrants removing the limbs or taking down the tree.

If he finds that the tree is still in good shape, he may recommend treating it with an insecticide. The usual type in these cases is a poisonous dust that ants carry back to their nest.
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