Japanese Beetles

What are Japanese Beetles?

Japanese beetles (Popillia japonica) are highly destructive, invasive insects that pose a serious threat to a wide variety of trees, shrubs, and plants across Missouri. Recognizable by their metallic green bodies and copper-colored wing covers, adult beetles may look small and harmless at first glance, but their feeding habits can quickly turn beautiful trees into skeletonized shells of their former selves.

Originally from Japan, these beetles were first detected in the United States in the early 1900s and have since spread across much of the eastern and midwestern U.S. In Missouri, especially in the St. Louis region, Japanese beetles are a seasonal nuisance that appear in large numbers from late spring through mid-summer.

While the adults feed voraciously on leaves, flowers, and fruit, their larvae, known as white grubs, live underground and feed on grassroots, causing damage to lawns and weakening trees from below. Together, the adult and larval stages make Japanese beetles one of the most difficult tree pests to control once they become established.

When do Japanese Beetles Come Out

In Missouri, Japanese beetles typically begin to emerge in early to mid-June, with peak activity occurring throughout July and early August. Their appearance is closely tied to soil temperatures—when the soil reaches about 60°F at a depth of 2 inches, the beetles begin to surface from their pupal stage underground.

Once they emerge, adult beetles are active for about 4 to 6 weeks, feeding aggressively on the foliage, flowers, and fruit of over 300 plant species. During this time, they also mate and lay eggs in nearby soil. The larvae (grubs) hatch a few weeks later and begin feeding on grassroots through the fall before going dormant for winter.

Key timing facts:

• Late May to Early June: First adult beetles may begin emerging in warmer years
  
  
• Mid-June to Early July: Main emergence period in Missouri
  
  
• July to Early August: Peak feeding and mating activity
  
  
• Late Summer: Eggs hatch and larvae begin feeding underground
  
  

Winter: Grubs overwinter in the soil and resume feeding in spring

What Do Japanese Beetles Looks LIke?

Japanese beetles are fairly easy to identify once you know what to look for. Their distinctive appearance and group-feeding habits make them stand out during the summer months.

Adult Japanese beetles:

• Roughly ½ inch long
  
  
• Metallic green head and thorax
  
  
• Copper-colored wing covers (elytra)
  
  
• Six white tufts of hair along each side of their abdomen (a key feature that sets them apart from other beetles)
  
  
• Usually seen in clusters feeding together on foliage and flowers
  
  

Larvae (white grubs):

• Found in the soil, especially in turfgrass
  
  
• C-shaped, creamy white with a brown head
  
  
• About 1 inch long at maturity
  
  
• Feed on grass roots, causing brown patches and thinning lawns
  
  

Signs You May Have Japanese Beetles

Japanese beetles cause visible and often widespread damage, particularly during peak feeding in mid-summer. Look for the following signs:

• Skeletonized Leaves
  
  This is the most common sign. Beetles feed on the soft tissue between leaf veins, leaving behind a lace-like “skeleton.” The damage often starts at the top of the tree and moves downward.
  
  
• Leaf Browning or Wilting
  
  Severely chewed leaves dry out quickly and may turn brown or fall off early, especially in hot weather.
  
  
• Clusters of Beetles on Leaves or Flowers
  
  Japanese beetles often feed in groups, especially on sunny days. You may see dozens clustered together on a single branch or flower.
  
  
• Defoliation
  
  In extreme cases, beetles can strip nearly all the leaves from a tree or shrub, leaving it bare.
  
  
• Damaged Fruit or Flowers
  
  They will also feed on ripening fruit and blossoms, causing cosmetic and structural damage to ornamental plants and fruit trees.
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• Turf Damage (Grub Stage)
  
  If your lawn has brown patches that peel up easily, you may have a grub infestation. These larvae feed on the roots of grass and other plants beneath the surface.
  
  

How Do Japanese Beetles Spread to Other Trees

Japanese beetles may seem slow and easy to catch, but their life cycle and behavior make them surprisingly effective at expanding across neighborhoods and landscapes. Here’s how they typically spread from tree to tree and yard to yard:

• Flight
  
  Adult Japanese beetles are strong fliers. Once they emerge, they can travel several miles in search of food or mates—especially if nearby trees and plants are already heavily infested or defoliated. This is the most common way they spread locally.
  
  
• Group Feeding Behavior
  
  Japanese beetles release pheromones that attract others to the same feeding site. When one tree becomes infested, nearby trees often follow as beetles gather in clusters and move outward over time.
  
  
• Egg-Laying in Turfgrass
  
  After mating, females lay eggs in nearby lawns or garden beds. These hatch into grubs, which live in the soil over winter and emerge as beetles the following summer. If untreated, this leads to a recurring annual cycle that naturally expands outward.
  
  
• Movement Through Nursery Stock and Soil
  
  Japanese beetle grubs can accidentally be introduced to new areas via the sale and transport of infested nursery plants, sod, or soil. While this is more of a regional or long-distance spread method, it’s a concern for landscapers and garden centers.
  
  
• Wind Assistance (Rare)
  
  Though not their primary method of travel, wind can occasionally help dislodge or carry beetles short distances—especially during peak activity periods when they’re flying between trees.
  
  

Trees Commonly Affected by Japanese Beetles in Missouri

• Linden Trees (Basswood)
  
  Linden trees are the most commonly targeted by Japanese beetles in Missouri. Their soft, fragrant leaves make them extremely attractive, and it’s not uncommon for beetles to completely defoliate them during peak season.
  
  
• Crabapple Trees
  
  These ornamental favorites are frequently attacked due to their tender leaves and fruit. Japanese beetles often gather in large numbers on crabapples, leading to visible damage throughout the canopy.
  
  
• Birch Trees
  
  River birch and other birch species are highly appealing to Japanese beetles. Their delicate leaves are easily skeletonized, and repeated feeding can weaken the tree over time.
  
  
• Elm Trees
  
  Both native and hybrid elms in Missouri are susceptible. Beetles typically feed on the upper canopy first, causing patchy leaf loss that worsens over the summer.
  
  
• Cherry & Plum Trees
  
  These fruit-bearing trees are attractive for both their leaves and sweet fruit. Japanese beetles can ruin fruit crops while also causing severe defoliation.
  
  
• Sycamore Trees
  
  While not the beetle’s top preference, sycamores still suffer moderate to heavy feeding, especially in sunny locations. Their large leaves offer ample surface area for beetles to gather and feed.
  
  
• Maples (Norway, Japanese, and others)
  
  Not all maples are heavily affected, but certain types like Norway and Japanese maple are more vulnerable. In high-pressure years, these trees can exhibit substantial foliar damage.
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• Horse Chestnut & Buckeye Trees
  
  These trees often attract beetles when planted near other infested trees. Their broad, compound leaves show clear signs of skeletonization during active feeding periods.