Asian Longhorned Beetles: What to Know

Medically Reviewed by Jabeen Begum, MD on January 13, 2023
4 min read

The Asian longhorned beetle is a type of longhorn beetle that poses a serious problem to hardwood forests. Although native to Asia, this invasive species has spread throughout parts of North America and Europe. To prevent further spread, many countries have established eradication programs to assess infected trees and destroy infestations of this insect. 

Asian longhorned beetle facts: 

  • Asian longhorned beetles likely came to North America and Europe through infested wood that was used to build shipping crates.
  • Adult female beetles eat small grooves out of trees so that they can lay their eggs. Once eggs hatch, the larvae live in and eat the tree for up to two years. 
  • It’s estimated that rampant infestation of the Asian longhorned beetle could kill over 30% of urban trees in the United States. 
  • Trees and forests infested with Asian longhorned beetles have to be quarantined and systematically eradicated to get rid of the insects.

Asian longhorned beetle appearance. Asian longhorned beetles are named for their long antennae, which are usually about 1.3 to 1.5 times as long as their bodies. The antennae are black with white stripes. These beetles are fairly large and can measure up to 1.5 inches long. 

Adult Asian longhorned beetles are all black with white dots on their wings, earning them the nickname “starry sky beetle”. Adult beetles have six legs and can fly but typically only do so for short distances. 

Asian longhorned beetle life cycle. Adult female beetles lay eggs in tree bark. The eggs hatch after about 11 days. After hatching, larvae eat their way into the tree. Larvae can stay in this stage for one to two years. 

Once larvae are ready to mature, they create a hollow chamber in the tree where they can pupate. The pupa develops for two to three weeks before an adult beetle emerges and tunnels itself out of the tree. 

What does the Asian longhorned beetle eat? Asian longhorned beetles in the larval stage burrow through trees, eating the wood as they go. Adult beetles are herbivores and tend to eat twigs and leaves.

Several species may be mistaken for Asian longhorned beetles. Citrus longhorned beetles, another invasive species, look the same as Asian longhorned beetles from a distance. If you look very closely, citrus longhorned beetles have bumps on their back that Asian longhorned beetles don’t have. 

Other species that look somewhat similar include:

  • White-spotted sawyers, which are much smaller than Asian longhorned beetles but colored similarly
  • Northern pine sawyers, which have grayish bodies rather than black
  • Cottonwood borers, which have a light body with black spots (the opposite of the black body with light spots seen on Asian longhorned beetles)

Asian longhorned beetles native range. Asian longhorned beetles are natively found in East Asia, most commonly throughout China, Japan, and Korea.

Asian longhorned beetles invasive range. Asian longhorned beetles have been present in North America since at least 1996, when they were first spotted in New York and Chicago. It’s believed that the beetles came from Asia through untreated wooden shipping crates.

These beetles spread easily, and are now found in most of the northeastern United States and in parts of eastern Canada. They have also been found in almost a dozen countries in Europe, including Austria, Italy, France, and the United Kingdom.

Asian longhorned beetles habitat. These beetles spend most of their life as larvae eating their way into trees. As adults, Asian longhorned beetles typically stay around hardwood forests and other areas with large amounts of hardwood, such as warehouses that store wooden crates.

Adult Asian longhorned beetles are hard to miss. Look for large, black beetles with white spots, particularly around any trees in the yard. 

Asian longhorned beetle damage. Adult Asian longhorned beetles are typically most active in the summer and fall. If you aren’t seeing any beetles but are worried about an infestation, you can look for certain signs of damage on trees, including:

  • Round exit holes in the trunk that adult beetles have emerged from
  • Frass, a byproduct of burrowing that looks like sawdust scattered around the branches and base of the tree trunk
  • Dark, circular stains on the trunk where eggs have been laid
  • Branch dieback, dead branches at the top of an otherwise healthy-looking tree, since infested trees tend to die from the top down

Unfortunately, there is not much you can do to prevent an infestation of Asian longhorned beetles. It can be difficult to tell if you have an infestation, as an infested tree may not die for 10 to 15 years, and larvae can infest a tree for a year or two before emerging as adult beetles. 

Asian longhorned beetles are not directly dangerous to humans. These beetles will not bite, poke, or sting you. However, Asian longhorned beetles can have significant indirect health impacts. 

The wood-boring nature of these beetles kills trees from the inside. Dead trees pose a significant hazard if left standing and are likely to drop limbs that can injure pedestrians and damage vehicles or even topple over entirely during storms.

Asian longhorned beetles are an invasive species that are usually dealt with by governmental agencies like the United States Department of Agriculture. These agencies typically have eradication programs that will quarantine affected areas and take down infected trees at no cost.

Asian longhorned beetle treatment. If you’re worried about a beetle infestation:

  • Contact your local eradication program before removing yard waste.
  • Do not sell or move any wood, including firewood, from potentially infested trees.
  • Use a compliant tree removal or landscaping company to dispose of any woody material.
  • Allow eradication program officials to inspect and remove infested trees.