Principle species colonised.
Unlike some specialists, the Asian Longhorn Beetle (ALB) is a generalist that attacks a wide variety of healthy broadleaf trees. In the UK, the most significant hosts include:
Identification.
The body colour is very shiny, “patent leather” jet black. The wing cases (elytra) are covered in roughly 20 irregular white spots (sometimes described as looking like a “starry sky”). Exceptionally long with alternating bands of black and white/pale blue. A large beetle, usually 20–40 mm in length (excluding the antennae).
In males the antennae can be up to twice the length of the body.
In females the antennae are roughly the same length as the body.
The legs are black but often have a unique bluish or whitish iridescent tinge, especially on the “feet” (tarsi). This is a helpful detail for distinguishing it from duller native beetles.
Type of symptoms.
Infestations are difficult to spot initially because the beetle spends most of its life hidden inside the wood. Look for perfectly round holes, about 10 mm in diameter (roughly the width of a pencil), usually found in the upper trunk and branches. Small, oval-shaped “scrapes” or notches in the bark where the female has chewed a hole to lay an egg. Trees may “weep” sap from these egg pits or from larval tunnels. Coarse, shredded wood shavings or sawdust-like waste pushed out of holes, often found trapped in branch forks or at the base of the tree. Adult beetles may strip the bark from young twigs or eat the veins of leaves.
The threat to host.
Larvae hatch and feed on the cambium (inner bark) before boring deep into the heartwood. This creates massive galleries (tunnels) that cut off the tree’s water and nutrient supply. The internal tunneling physically weakens the timber. This makes branches or the main trunk highly susceptible to snapping during wind or storms, even while the tree still appears green.
Repeated infestations over several years will eventually kill even a large, healthy mature tree.
Impact / Effect / Significance
The UK’s timber, nursery, and fruit industries face millions of pounds in potential losses. The 2012 eradication effort required felling over 2,000 trees to eliminate just 66 infested ones. It threatens our most iconic landscape trees. A widespread establishment would permanently alter British woodlands, parks, and urban avenues.
Because the beetle weakens tree structures from the inside, it creates a significant “fall risk” in public parks and residential gardens. The UK is currently officially free of ALB. To maintain this, any suspected sighting must be reported to the Forestry Commission.
