Asian longhorned beetle
Anoplophora glabripennis
A large black beetle with white spots and enormous banded antennae, bored deep into maple heartwood. If you see one, take a photograph and report it.
How to know it
Unmistakable and large: a glossy black beetle 20–35 mm long with irregular white spots on the wing cases and antennae longer than its body, banded in black and white. The exit hole is round, clean and about a centimeter across — big enough to put a pencil in, which is the quick field test that separates it from every native borer.
What you'll see
- Round exit holes about a centimeter wide, deep enough to take a pencil, in the trunk and main branches.
- Coarse sawdust-like frass piled at the base of the tree and in branch crotches.
- Shallow oval egg-laying pits chewed into the bark, often weeping sap.
- Branches dying and dropping, and a crown thinning over several years.
- The beetle itself, which is large and conspicuous and flies in late summer.
Where it comes from
One generation a year, or two years in cooler areas. Females chew a pit in the bark and lay a single egg in it; the grub tunnels deep into the heartwood, not just the surface tissue, which is why the damage is structural and why treatment is so difficult. Adults emerge from midsummer through autumn. It spreads mainly in wood packaging and firewood.
Introduced repeatedly in wooden packing crates and eradicated at heavy cost from several North American cities. Active quarantine zones exist and change; maples in and near an urban area are the usual finding place.
Dealing with it
- Report it. This is a federally regulated pest, eradication programs are active, and reporting a first find is genuinely the most useful thing you can do.
- Photograph the beetle and, if you can do it safely, capture it in a jar and freeze it.
- Note the exact tree and location; the eradication surveys work outward from confirmed finds.
- Do not remove or move the tree or the wood yourself; the program will direct it.
- Do not treat it yourself — no garden treatment reaches a grub in the heartwood.
Keeping it out
- Do not move firewood, and buy it where you burn it.
- Learn the beetle. It is large, distinctive and easy to recognize from a photograph.
- Report any large black-and-white longhorned beetle, even if you think it is a native; the surveys would far rather have a false alarm.
- Inspect maples for large round exit holes and for coarse frass in the branch crotches.
- Plant a diverse mix rather than a street or a garden of maples.
What it goes for
Maples above all, then birch, willow, poplar, elm, horse chestnut and London plane.
See also
The Cottage Garden Companion — the gardener's bestiary at cottagegardencompanion.com