Emerald Ash Borer vs Asian Longhorned Beetle: How to Tell the Difference
Compare two of North America's most destructive invasive wood-boring insects: the emerald ash borer and the Asian longhorned beetle.
At a Glance
Emerald Ash Borer
MODERATE- Type
- Insect
- Severity
- MODERATE
- Affected States
- 36 total (36 active)
Symptoms
Canopy dieback starting at the top of the tree, D-shaped exit holes in bark, serpentine larval galleries under bark, increased woodpecker activity, epicormic sprouting along the trunk
Asian Longhorned Beetle
CRITICAL- Type
- Insect
- Severity
- CRITICAL
- Affected States
- 5 total (0 active)
Symptoms
Round exit holes approximately 3/8 inch in diameter, frass (sawdust) at base of tree and branch crotches, pitted egg-laying sites on bark, branch dieback in upper canopy
Similarities
What makes Emerald Ash Borer and Asian Longhorned Beetle easy to confuse:
- Both are invasive wood-boring beetles from Asia introduced to North America
- Both larvae tunnel under bark and through wood, disrupting nutrient transport
- Both have caused billions of dollars in damage to urban and forest trees
- Both are spread primarily through movement of infested firewood and wood products
- Both are subject to federal and state quarantine regulations
Key Differences
| Feature | Emerald Ash Borer (EAB) | Asian Longhorned Beetle (ALB) |
|---|---|---|
| Appearance | Small (8-14mm), metallic emerald green | Large (20-35mm), glossy black with white spots, long antennae |
| Target trees | Exclusively ash trees (*Fraxinus* species) | Broad host range: maples, elms, birches, willows, and more |
| Exit holes | D-shaped exit holes (3-4mm) | Round exit holes (10mm+ diameter) |
| Gallery pattern | S-shaped serpentine galleries under bark | Deep tunnels into heartwood |
| Current spread | Found in 35+ states; widespread | Eradicated in some areas; limited active infestations |
| Adult activity | Adults feed on ash foliage; minimal visible damage | Adults chew oval pits in bark for egg-laying |
How to Tell Them Apart
- Identify the host tree first: If the affected tree is an ash (compound leaves with 5-9 leaflets), suspect EAB. If it is a maple, birch, elm, or willow, suspect ALB.
- Examine exit holes: EAB exit holes are distinctly D-shaped and small (about 3-4mm). ALB exit holes are perfectly round and large (about 10mm or wider, roughly pencil-sized).
- Look at the beetle itself: EAB adults are small and brilliant metallic green. ALB adults are large, shiny black with irregular white spots, and have antennae longer than their body.
- Check for sawdust: ALB produces coarse sawdust (frass) at the base of trees and from exit holes. EAB frass is fine and found packed in serpentine galleries under the bark.
- Inspect canopy decline pattern: EAB typically causes dieback starting in the upper crown and progressing downward over 2-4 years. ALB damage can appear anywhere on the tree.
Frequently Asked Questions
Which beetle is more destructive?
The emerald ash borer has killed hundreds of millions of ash trees across North America and is considered one of the most destructive forest insects ever to invade the continent. The ALB is equally lethal to individual trees but has been more successfully contained through eradication programs.
Can both beetles infest the same tree?
No. EAB exclusively attacks ash trees, while ALB does not typically target ash. Their host tree preferences do not overlap significantly.
How are these beetles spread?
Both beetles are primarily spread through human transport of infested firewood, lumber, and wood packing materials. This is why "Don't Move Firewood" campaigns are critical for preventing further spread.
What should I do if I find one of these beetles?
Report any suspected sighting immediately. Contact your state forestry agency or USDA APHIS. For ALB, take a photo and call the ALB hotline. Early detection is critical for eradication efforts.
Are there treatments available?
For EAB, systemic insecticide treatments (such as emamectin benzoate trunk injections) can protect individual ash trees if applied before significant decline. There is no chemical treatment for ALB; infested trees must be removed and chipped.