Destructive Emerald Ash Borer Beetles: Identification And Signs Of Infestation

Emerald ash borer beetles (EAB) are costing cities, companies and property owners millions of dollars because of damage caused by their invasion of ash trees. Unless these infestations are stopped, the economic impact will continue to worsen for industries that rely on this type of lumber. Because of the continual spread of EAB infestations, learning to identify EABs and the signs of infestation are critical so they can be stopped.

Identifying the Emerald Ash Borer

It can be challenging identifying the emerald ash borer because there are other types of beetles that look very similar to it. Plus, during the pre-adult stages of the EAB lifecycle, you must rip the bark from a tree in order to spot them because these beetles live in small chambers they've built beneath the bark.

  • Adult: An adult emerald ash borer has a metallic green body with purple areas beneath its wings. Its entire body is about a half-inch long and it has a flattened back.
  • Pupae: After one to two years of feeding inside the bark of an ash tree, the EAB larvae build small tunnels and chambers for themselves in the layers below the bark, known as the sapwood. In the spring, the EAB pupae emerge from the tree as adults.  This is the lifecycle stage between larvae and adulthood.
  • Larvae: Immature emerald ash borers, or larvae, have lightly flattened bodies that are white with two brown pinchers on the very end. They vary in size, depending on how much they feed and grow beneath an ash tree's bark.
  • Egg: The eggs of an EAB are only about one millimeter long, making them very difficult to spot. After the adult female deposits them into crevices within the tree bark, they hatch from the eggs and immediately begin boring their way deeper into the tree.

How EAB Infestation Spreads

Emerald ash borers typically only fly a distance of about a half-mile, so infestation is spread by humans who inadvertently transport firewood, logs, branches, chips and other raw ash wood products infested with larvae.

This destructive beetle was first discovered in North America in 2002, just outside Detroit. Since then, EAB infestation has spread to Canada and at least 22 other states. Since emerald ash borers originate in Asia, infestations in the U.S. and Canada also spread from larvae-infested wood products imported from the Far East.  

Signs of EAB Infestation

Emerald ash borer beetles are responsible for killing tens of millions of ash trees throughout North America, so it's crucial to identify the signs of infestation as soon as possible. An EAB-infested tree can die within two to four years because EAB larvae feed on the sapwood and inner bark, causing the tree to starve as it loses its ability to transport nutrients and water from its roots to the rest of the tree.

  • Dieback of the Tree's Canopy: The upper and outer canopy of a tree begins to die after years of EAB infestation. Dead branches appear throughout the canopy, beginning near the top.
  • Epicormic Sprouts: As an EAB-infested tree becomes sicker, it may try to grow new branches and leaves from the area of the trunk located below the larvae infestation. This usually occurs near the base of the tree.
  • Splitting Bark: An infested tree often has long, vertical splits in the bark caused by larval boring and feeding.
  • Increased Woodpecker Interest: Woodpeckers like to eat EAB larvae beneath the bark. When woodpeckers forage for these beetles, they create holes in the tree. In a highly infested tree, woodpecker damage may appear as long strips of missing bark.
  • D-Shaped Holes: An abundance of tiny holes shaped like the letter "D" in the tree's outer bark is a sign of EAB damage because they use these holes to emerge from the tree.
  • S-Shaped Patterns: As larvae feed on the sapwood beneath the bark, they wind back and forth, creating long S-shaped patterns. These patterns are not visible unless the outer layer of bark has been removed.

One of the most effective ways to stop the spread of EAB infestation is to avoid moving ash firewood across state lines. If you do notice any signs of emerald ash borer beetles, contact your local town office for more information.