How to identify an Asian Longhorned Beetle

How to identify an Asian Longhorned Beetle

You can identify an Asian Longhorned Beetle by four features together: a large (1–1.5 inch), glossy jet-black body; irregular white spots across the wing covers; long antennae boldly banded in black and white; and, on the tree, round exit holes about the width of a pencil. No single trait is proof on its own — a native beetle may share one — but the combination is distinctive, and the black-and-white banded antennae are the signature mark to look for first.

• Size: roughly 1 to 1.5 inches (2.5–3.8 cm) long — a big beetle.
• Color: shiny, almost lacquered black.
• Spots: up to about 20 white spots on each wing cover (they are actually clumps of white hairs).
• Antennae: longer than the body, with clean alternating black-and-white bands.
• Legs: six legs, often with a bluish-white cast to the feet.

Where you see the beetle matters too. Adults are most often noticed resting on tree trunks and large branches, on nearby structures like fences and lawn furniture, or bumping against windows and cars parked under host trees on a warm summer day. They are slow, conspicuous, and easy to photograph — you rarely have to catch one in flight. If a big black-and-white beetle is sitting calmly on a maple in July or August, it deserves a careful look.

Size, color, and markings

The adult beetle's coloring is its most recognizable feature: a glossy black body scattered with white spots, and antennae that are not just long but clearly striped. Females are typically a little larger than males, while males carry the longest antennae — up to roughly two and a half times their body length, versus a little over body length in females. The card below captures the marks to check.

A few finer points help confirm an identification. The white spots are not painted-on dots but clumps of short white hairs, so they can look slightly raised or fuzzy up close, and their number varies — some beetles are heavily speckled while others are nearly all black. The antennal bands are crisp and regular, alternating black and white segment by segment, and the body has a genuine lacquered shine, not the dull or bronzed finish of the native beetles below. Any one of these can be ambiguous alone; together, on a hardwood tree, they point clearly to ALB.

What its exit holes and damage look like

The clearest sign an Asian Longhorned Beetle has been in a tree is a perfectly round exit hole about ⅜ inch across — roughly the width of a pencil, and deep enough that you often cannot see the bottom. Adults chew these holes to escape the wood after they mature. Alongside the exit holes, look for the other tells of an active infestation:

• Round exit holes, about ⅜ inch (0.37–0.48 in) in diameter, often on the upper trunk and larger branches.
• Oval egg-laying pits chewed into the bark, roughly ½ to ¾ inch across.
• Coarse, sawdust-like frass piled in branch crotches and around the tree base.
• Sap oozing from wounds, leaving dark streaks on the bark.
• Dead limbs and off-season yellowing as tunneling girdles the canopy.

These signs are covered in more depth, tree by tree, in damage and host trees. The life cycle explains why the exit holes only appear once the hidden larval stage is over.

Look-alikes and how to tell them apart

The beetles most often mistaken for the Asian Longhorned Beetle are native, harmless, and — in the most common cases — live on conifers, which ALB never touches. The quickest separators are the antennae (ALB's are boldly black-and-white banded; the sawyers' are more uniform) and the host tree (ALB on hardwoods, especially maple; the sawyers on pines and spruces). This table gives the one distinguishing feature for each; the cards below show them individually.

If you remember nothing else, two questions settle most cases. First, are the antennae boldly banded black and white? The native sawyers and the cottonwood borer do not have that clean banded pattern. Second, what tree was it on? ALB attacks hardwoods — maple, birch, willow, elm — and never conifers, so a large beetle found on a pine or spruce is almost certainly a harmless native sawyer. When the antennae are banded and the tree is a hardwood, treat it as a possible ALB and report it rather than trying to be certain yourself.

What to do if your beetle matches

If your beetle has the glossy black body, white spots, and boldly banded antennae — and you found it on a hardwood like maple — treat it as a possible Asian Longhorned Beetle and report it. You do not need to be certain; that is what the inspectors are for. Photograph it from a few angles with something for scale, and if you can safely do so, capture it in a sealed container so it can be confirmed. Then report it through the official channel below.