The emerald ash borer (Agrilus planipennis) is a small metallic-green beetle from Asia that has killed hundreds of millions of ash trees across North America since it was discovered near Detroit in 2002. The adult beetle is easy to miss; the signs of its larvae in a dying ash are what usually give it away. Here is what to look for.
How to Identify the Emerald Ash Borer
- Adult beetle: slender, about a half-inch long, brilliant metallic emerald-green, with a coppery-red upper abdomen visible under the wings
- Exit holes: distinctive D-shaped holes about 1/8 inch wide in the bark
- Larval galleries: winding, S-shaped tunnels packed with sawdust just under the bark
- Tree symptoms: thinning canopy, dead branches at the top, sprouts along the trunk, and woodpeckers stripping bark ("blonding")
Why It Matters
The larvae tunnel through the layer that carries water and nutrients, girdling the tree from the inside. An infested ash usually dies within two to four years. Because ash was planted so widely as a street and yard tree, the borer has reshaped entire urban and forest canopies.
What to Do
- If you have valuable ash trees, ask a certified arborist about protective treatments — they work best before heavy infestation
- Never transport firewood; buy or gather it where you burn it
- Report suspected infestations to your state agriculture or forestry agency
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