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Japanese Beetle — Facts and Control

If you see a hard red shell with black spots, you probably automatically assume it's a friendly ladybug. But those little bugs in your garden could actually be a type of beetle that infiltrates your home, bites, and produce a foul-smelling odor similar to stink bugs. While Japanese beetles share some similarities with ladybugs, they're becoming a problem for many homeowners and gardeners, and are overtaking the native ladybug population. If you can tell the difference between the two beetles, you might be able to stop an annoying problem before it starts.

Graphic showing comparision between ladybug and Japanese beetle.

How To Identify Ladybugs

These beetles are beneficial to your garden and harmless to humans. They don't bite and consume garden pests like aphids and scale insects. When the weather cools down, ladybugs seek shelter outside and they don't congregate in large numbers.

You can identify a ladybug by its markings and size. They have bright, cherry-red shells with black spots, and their heads are black with small white "cheeks." Ladybugs are typically rounder and smaller than Japanese beetles if you look at them side-by-side.

 For basic information on Ladybugs, see Ladybugs: Beneficial Insect  

How To identify Japanese Beetles

To tell the difference between a Japanese beetle and a ladybug, look at the spot where the head meets the wings. If the bug has a small white 'M' marking in that spot, that's a telltale sign you're dealing with an invasive species. They also have larger white "cheek" markings and have more white on their heads overall. Their shell color can range from light orange to bright red, so most will have a similar color to a ladybug.

Japanese beetle inside a dog's mouth. Japanese beetles are known to sneak into your home through cracks or holes when it gets cold outside and congregate on siding, doors, and windows. They're more aggressive than ladybugs and bite by scraping the skin they land on. If they feel threatened, they'll excrete a foul-smelling yellow liquid from their legs that can stain surfaces and trigger allergic reactions.

While it isn't common, Japanese beetles can infest dogs' mouths. Since they look for a warm shelter in winter, they attach to the roof of the mouths of dogs. While this won't always mean a trip to the emergency vet, it will still be very uncomfortable and unpleasant for them. If they swallow the beetles, the yellow liquid can burn the dog's mouth or gastrointestinal tract. The symptoms include excessive drooling and the insects can be removed from the dog’s mouth with a spoon or a tongue depressor.

Life Cycle

Graphic of japanese beetle life cycle.

  Egg laying begins soon after the adults emerge from the ground and mate.
  Females leave plants in the afternoon, burrow 2 to 3 inches into the soil in a suitable area, and lay their eggs--a total of 40 to 60 during their life.
  The developing beetles spend the next 10 months in the soil as white grubs.
  Grubs feed on the roots of turf grasses and vegetable seedlings
  Japanese beetles overwinter in the grub stage.
  Grubs pass the winter 2 to 6 inches below the surface, although some may go as deep as 8 to 10 inches.
  When soil temperature climbs above 50°F in the spring, the grubs begin to move up into the root zone
  Following a feeding period of 4-6 weeks, the grubs pupate in an earthen cell and remain there until emerging as adults.

How To Control Japanese Beetles

Beetle Anatomy. The best way to keep Japanese lady beetles out of your home is by sealing and patching potential entrance points. Close up any gaps around windows, doors, and siding to minimize risk. If they do get into your home, try not to squash them, or they'll release their smelly yellow liquid. The best way to avoid odor and stains is to vacuum them and empty the vacuum when you're done. Contain the Japanese beetles in a sealed bag before tossing into the trash so they can't crawl out.

Outdoors, you can clear them off the areas the beetles usually congregate and scrub down the area with soapy water; they most likely won't return because the soap smell overpowers the pheromones that attract more beetles to the location. They especially don't like the scent of citrus, cloves, or bay leaves

You can also take measures to attract native ladybugs to your garden and they will push the Japanese beetles out. Avoid using chemicals in the garden and grow pollen-rich flowers. They're attracted to light and bright colors, so look for white and yellow flower varieties.

Biological Control of Grubs

Although there are a few biological control products that allegedly control Japanese beetle grubs, the performance of these products has been inconsistent. Biological control products include milky spore disease, insect-parasitic nematodes, and fungal pathogens such as Beauveria bassiana and Metarrhiizium.

Japanese Beetle Traps

Japanese beetle trap According to expert Dr. Michael Klein, pheromone Japanese beetle traps are the most effective, environmentally friendly method of combating Japanese beetles. Over the years, he has used pheromone traps to protect the prized rose bushes and other plants in his own back yard.

Japanese beetle traps only lure beetles that are already near the yard. Attractants lure beetles from no more than 200 yards. Problems can occur when Japanese beetle traps are placed incorrectly. If placed next to a rose bush, Japanese beetles will be attracted to that area, and may land on the roses rather than in the trap.

  Don't place traps next to ornamental plants. Set traps about 30 feet from tasty plants to lure the beetles away.

  It's best to place traps next to a non-flowering tree or shrub such as a pine or boxwood.

  Place the trap about 4 feet above the ground.

  Enlist neighbors to battle the beetles with you. Traps are effective in one yard alone, but when neighbors band together and put out traps in their yards, the overall beetle numbers are greatly reduced.

Further Information on Garden Pests:

 Groundhog Facts and Control
 YIKES! Jumping Worms
 How To Get Rid Of Ants
 All About Aphids and Their Control
 Voles — Both the Good and the Bad

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