Tiny, dime-sized holes in the trunk look harmless enough, butcan lead to the death of a favorite tree.

They are the marks of tree borers—insects that feed and reproduce on old or weak trees.

The bugs drill into the tree’s cambium layer, which is right under the bark and carries the nutrients, said John Turner of the University of Arkansas’ Division of Agriculture. “They will eat that layer out and once they get in there there’s really nothing you can do.”

Often named for the type of tree it is found in, such as an oak borer or maple borer, there are two type...

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