Emerald ash borer identification starts with a small metallic-green beetle, but the insect is only one part of the picture. Knowing its distinguishing features and the signs to look for on ash trees can help you separate a likely sighting from a look-alike.
What does an emerald ash borer look like?
The emerald ash borer (Agrilus planipennis) is a slender, elongated beetle in the metallic wood-boring beetle family Buprestidae. Adults are typically about 8 to 14 millimeters long, roughly the length of a small paper clip segment, and about 3 millimeters wide. Their bodies are narrow and slightly flattened, with a tapered rear end.
The most recognizable feature is the adult’s bright, metallic green upper surface. In good light, the wing covers and thorax can shine emerald, bronze-green, or coppery-green. The underside is usually a vivid metallic purplish-red or copper color, but it may be difficult to see without handling or turning the beetle. Color can also look duller in shade, in photographs, or on a worn specimen.
Adults have short antennae and hard wing covers that meet in a straight line down the back. The body shape and metallic coloring are useful clues, but neither is conclusive by itself: many native beetles also have shiny green or bronze bodies.
How can you distinguish it from similar beetles?
Several beetles may be mistaken for emerald ash borer, especially when seen briefly or in a low-quality photograph. Compare overall size, body shape, color, and where the insect was found. A beetle on or near an ash tree deserves closer attention, but location alone does not confirm the species.
| Feature | Emerald ash borer | Common look-alike clues |
|---|---|---|
| Length and shape | About 8–14 mm; narrow, elongated, tapered body | Some metallic wood-boring beetles are larger, broader, or more cylindrical |
| Color | Metallic green upper surface; often reddish-purple underside | Green leaf beetles may be rounder, while other jewel beetles can be bronze or blue-green |
| Tree association | Larvae develop beneath the bark of ash trees | A beetle found on foliage or another tree may be an unrelated species |
| Tree signs | D-shaped exit holes and serpentine galleries may occur on infested ash | Cracks, holes, and bark damage can have other causes |
Use the table as a screening aid rather than a definitive identification key. Native metallic beetles vary widely, and color can shift with lighting and camera settings. A clear photograph showing the insect’s back, side, and approximate size can make expert review more useful.
What signs can appear on an ash tree?
Emerald ash borer larvae feed in the living tissue beneath the bark. Their winding, S-shaped galleries can disrupt the movement of water and nutrients through the tree. If the bark is lifted, galleries may be visible in the inner bark, sometimes packed with fine frass. Do not peel bark from a living tree to search for them; many other organisms and injuries can also mark beneath-bark tissue.
Adult beetles leave small, D-shaped exit holes as they emerge through the bark. These are typically around 3 to 4 millimeters wide, with a flat edge and rounded opposite side. Hole shape is a useful clue, but old holes can be hard to interpret, and other insects or physical damage may create openings that look similar.
As an infestation affects more of a tree, possible signs include thinning foliage, branches dying back from the crown, vertical bark splits, and increased shoots growing from the trunk or base. Woodpeckers may remove bark while searching for larvae, exposing lighter patches. These symptoms are not unique to emerald ash borer; drought, disease, root problems, and other pests can produce similar decline.
Which trees are potential hosts?
Emerald ash borer develops in ash trees in the genus Fraxinus. Common North American hosts include white ash, green ash, and black ash, along with other ash species. Mountain ash (rowan, Sorbus) is not a true ash in the genus Fraxinus, so the shared common name can cause confusion.
Confirm the tree’s identity before using its condition as supporting evidence. Ash trees generally have opposite branching: twigs, buds, and leaves tend to emerge in pairs across from one another. Compound leaves usually have several leaflets arranged along a central stem. These characteristics can help, but leafless trees and damaged branches may be harder to identify.
How should you document a possible sighting?
- Photograph the beetle in focus from above and, if possible without touching it, from the side. Include a familiar object nearby for scale.
- Record the date, general location, and the tree or surface where you found it. Avoid posting precise private-property details publicly.
- If you can identify the tree confidently, note the ash species or photograph its leaves, buds, and branching pattern.
- Photograph suspected D-shaped holes or canopy symptoms from a distance. Do not cut, transport, or remove wood or bark to investigate.
Submit the observations to your local forestry, agriculture, or plant-health authority, following its current reporting guidance. Reporting channels and regulations differ by location. A qualified specialist may need additional views or local context to distinguish emerald ash borer from similar beetles or to evaluate tree decline.
What can a photograph establish?
A photograph can support a preliminary identification when it clearly shows body shape, metallic coloring, and scale. It may not reveal the underside, fine structural features, or details needed to separate similar species. A single image of a green beetle, a D-shaped opening, or a thinning tree is not enough on its own to confirm emerald ash borer.
For the strongest assessment, combine insect photos, tree identification, location, and any observed signs, then seek review from the relevant local authority or an entomology extension service. Treat uncertainty as part of the identification process, particularly when the photograph is blurry, the specimen is damaged, or the host tree is unknown.