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Dealing with Japanese Beetles
April 01, 2013

Welcome to the Flying Butterfly!


Up until last year I had a few Japanese Beetles (Popillia japonica) visit
on occasion. It wasn't until I purchased a must have Limelight Hydrangea tree that I noticed these insects felt the same way about it as I did - must have! This year I am going in armed and should you find these insects are a problem for you to, here's the 411.





Japanese Beetles were introduced to North America in 1916. Currently they are found more in the eastern United States but are moving west.


The adult beetle has fine hairs are all over it's body. These fine hairs create the dotted white markings seen in this picture. The insects backside is metallic green with bronze wing covers.



Their body length averages 1/2" and body width is about 1/4". Life span for the Japanese Beetle is between 30-45 days. When threatened beetles will either stick up their two back legs giving warning to any potential threat or tuck in all legs then drop off of plants they are on.

As with emerging butterflies, adult beetles emerge to mate and reproduce to expand their species. More often in group settings, when beetles take a break from mating they are feeding on our butterfly garden.



They eat entire leaf surfaces
where only the veins of leaf remain,
looking skeletonized. Flower petals
and buds can be eaten as well.


While feeding, beetles release pheromones (sex hormones) to lure in more beetles to mate with. Burrowing deep into the ground, the female then lays her eggs and moves back to the surface. After about two weeks the eggs hatch into larva. The larva then travel deeper into the soil.

The larvae are plump and resemble the letter 'C'. Larva coloring is dirty gray to white, heads are light brown. Larva average 3/4" but can grow
up to 1-1/2". Note that Japanese beetle larva are also called grubs, whereas butterfly larva are called caterpillars.

Japanese beetle grubs overwinter several inches underground where they eat and grow constantly then go dormant for about 10 days. With spring's heat they make their way up to soil surface.

On their way up to the surface, grubs feed on lawn grasses, ornamental grasses and garden plant roots. The result of all of this eating are irregular brown patches that resemble loose carpeting.

When these carpet-like patches are peeled back the larvae underneath are quite visible. This lawn damage becomes obvious late spring through early fall, especially during dry spells.

Pupatation of larvae occurs in early summer and lasts anywhere from 8-20 days. After this adults begin to emerge for much of the U.S about the last week of June.

Beetles feed on over 300 species of plants. They really like Roses and other yummy plants include Cherry trees, Plum trees, Japanese maple trees, Corn silks, Grapes, Raspberries, Rhubarb, Zinnias, Hollyhocks,
Crape myrtle and yes, Limelight hydrangea trees.



Ways to Eliminate

    As a rule of thumb regardless of where one lives in the country, when adult beetles start actively flying around in summer this is when a lot of mating is going on. From the time where you see adults mating wait 5-6 weeks and then use the more intense
    control methods farther down this list.

Homemade or more organic methods:


1) There are traps designed to rid Japanese beetles. These are not as effective as other methods and have been known to do the reverse
where they attract beetles. These use pheromones or scents as bait - populations can multiply. If you opt to try these it is recommended to place trap several hundred feet from lawn and garden.

2) Soapy Water - Insects having an exoskeleton can deteriorate from inside and sometimes it is suggested spraying plant with strong detergent water. This isn't as effective. Many beetles dig legs into leaf and can survive only to be back doing what they do best, like butterflies ;-). Spraying soapy water on plants can possibly harm good insects like butterflies, which also have an exoskeleton.

  • Instead knock adult beetles off into a container of soapy water drowning them. Make sure they're dead by squishing them. This helps in preventing populations from exploding by getting started early once you first spot them. Grubs can also be placed in soapy water.

  • The best time of day to pick off plants is morning and evening. Mid-day they are more likely to fly away. Japanese Beetles don't come out on rainy days. They prefer days with low humidity and full sun exposure with temperatures between 85-95 degrees. Take into consideration of eastern sun exposure in morning and afternoons when planting vegetation.

  • Beetles and Grubs are a tasty treat for many birds, especially crows. Consider putting insects in water only, squish them and place in a container or on the soil for consumption.

  • Other animals that like the grubs are skunks, moles and racoons. If these animals come to an area frequently, it is a good sign that there is a serious grub population.

3) Because beetles like grapes, place some grape juice in a separate container in the middle of a pan that has soapy water in it. Place this at least 25' from the plant beetles are on. They will find grape juice easily.


4) One Geranium, Geranium maculatum,
is poisonous to beetles. When beetles chew on them, they die. This is a perennial wildflower found more predominately along the middle to eastern portions of North America. Consider planting geranium maculatum close to Japanese beetle infested plants or in a natural garden where butterflies can enjoy a meal.


5) During mating season grab a plastic bag and pour 1-2 teaspoons of rose-anise or fennel oil (found at craft or health food stores) to attract beetles. Japanese beetles are also drawn to yellow. Roll yellow construction or craft paper into a funnel and tape bottom of funnel into the bag. Hang funnel and bag about 25 feet from plants to lure them in.

6) Because eggs and young grubs need moisture, late summer is when females lay eggs. Avoid watering lawn in effected area during these times to avoid larva from hatching.

7) Plants that Japanese beetles won't fly to include Garlic, Rue, Tansy, Larkspur and White Geraniums. So when planting consider putting vegetation that they won't go near next plants they do enjoy.


Other preventitive actions include:

For Japanese beetle grubs use Milky Spore Disease (Bacillus popilliae).
    This is a natural bacteria that controls grubs, not harming any other soil life or mammal's. It is purchased in granular form and it's effects can last up to 15 years. Read directions - See suppliers of organic products and gardening centers.

    Milky Spore usually takes a few years to take effect, so you may need alternatives until this time.


More intense control methods:

1) Spray plants attacked by beetles with Rotenone. This is an odorless, colorless broad-spectrum insecticide that can be found at many garden supply stores. Read instructions well.

2) Neem - This is an organic pesticide made from seeds of the tropical Neem tree and a more expensive alternative. Good for repelling many insects, including Aphids and mealy bugs, It suppresses feeding and molting. It is not harmful to soil life or mammals but too much can be harmful to beneficial pollinators. Read instructions carefully. Found at suppliers of organic products and some garden centers.

3) Pyrethrins, derived from a species of Chrysanthemum, will attack pests nervous system. Use the natural pyrethrins and not synthetic, non-organic, which are called pyrethroids.

This is the stuff you use when all else fails. This organic pesticide can harm many beneficial insects. Use when populations are out of control. Like Neem, pyrethrins combat many destructive pests but also many beneficial insects. Found at suppliers of organic products and some
garden centers.


Biological control:

1) Parasitic Wasp - A beneficial nematode, or microscopic roundworm. Nematodes can be both beneficial or detrimental. Some species of beneficial nematodes can be purchased.



It is important to read directions carefully and apply the proper species of nematode best suited for your needs. In this case - Japaneese Beetles. Must re-apply parasitic wasp every spring.





It's a lot to take in but also a good place to start if you may find yourself having Japanese Beetle problems. Happy springtime!
It's time to get out and clean our gardens. Yeah!


Elizabeth @ Easy Butterfly Garden



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