About Japanese beetle traps
What is the purpose of Japanese beetle traps?
Japanese beetle traps help protect plants and trees from being eaten by adult Japanese beetles. Once Japanese beetles begin eating a plant, they quickly “skeletonize” the leaves—filling them with large, irregular holes. Left unchecked, Japanese beetles can cause extensive and permanent damage.
The traps also help assess the Japanese beetle population in an area. If a trap becomes filled in one day, the surrounding area is most likely experiencing a Japanese beetle infestation. However, a trap that is barely filled after a week indicates an area with a minimal problem.
What attracts Japanese beetles?
The question should probably be “what doesn’t attract Japanese beetles” because the list might be shorter. Japanese beetles are attracted to a wide variety of field crops, ornamental trees, shrubs, garden flowers, and vegetables—almost 300 different species.
Japanese beetles prefer to lay their eggs in the turf of lawns, pastures, and golf courses. They also like the odor of diseased or rotting fruit.
Who typically uses Japanese beetle traps?
Gardeners and homeowners who want to protect their plants and trees from Japanese beetles are the primary users of the traps. The beetles are particularly attracted to treasured plants (like roses) and expensive ornamental trees (like Japanese maples). Farmers and orchard owners also use Japanese beetle traps to protect their trees and crops from damage.
How does a Japanese beetle trap work?
Japanese beetle traps have a relatively simple construction, with only two main parts—the lure and the bag (also known as Japanese beetle bags).
Once the beetles fly to the lure (which is located near the top of the attached bag), they crawl into or fall into the bag, where they become trapped and cannot escape. The bag fills with more beetles until it needs to be emptied or replaced. The traps must be hung from hooks or posts at the optimum height to attract beetles.
Most traps use plastic bags that can be removed and replaced as needed. One of our top choices (the Tanglewood trap) uses a hard-plastic trap that can be emptied, cleaned, and reused.
Do Japanese beetle traps work?
Yes! The traps are extremely effective at attracting and capturing Japanese beetles. However, one criticism of Japanese beetle traps is that they are too efficient—drawing such large numbers of beetles to them that they cannot trap them all. The “excess” beetles then land and feed on nearby plants. Tips for dealing with this are provided in the “Tips for using Japanese beetle traps” section below.
Are there alternatives to using Japanese beetle traps?
There are several alternatives to using Japanese beetle traps, each with their own benefits and drawbacks. Some methods are best used in conjunction with the traps. For example, targeting the grubs that will become next year’s adult beetles helps to reduce the overall beetle population.
Alternatives to Japanese beetle traps include the following:
- Pyrethrin-based insecticides. However, traps are more environmentally friendly than spray insecticides, which can harm helpful insects, such as honeybees and butterflies.
- Neem oil is a natural, non-toxic pesticide derived from the neem tree. When sprayed on plants, it helps control Japanese beetles (as well as a host of other pests) by causing them to stop feeding on the plants.
- Hand picking. Instead of using traps, some gardeners use a more hands-on approach—literally! Every morning when the beetles are sluggish, you can pick them off by hand and drop them in a bucket of soapy water. Even when they are more alert, Japanese beetles are slow and easy to catch.
- Biological control. Although biological control doesn’t provide an immediate way to eliminate the adult beetles eating your plants, they can be used to kill the grubs that will become next year’s adult beetles. One option is Beneficial Nematodes —microscopic parasitic roundworms that actively seek out and kill grubs in the soil. For Japanese beetles, the most effective are Steinernema glaseri and Heterorhabditis bacteriophora. Another option is to use soil bacteriums that affect the development of Japanese beetle grubs. Options are Bacillus thuringiensis and Bacillus papillae (also known as milky spore). These options can take as long as 2 to 4 years to become effective.
- Parasites. Releasing natural enemies or parasites of Japanese beetles can help reduce the population. Two such parasites (Tiphia vernalis and Istocheta aldrichi) are being studied by the USDA, but are not yet commercially available.
- Habitat Manipulation involves planting trees and plants that are less susceptible to Japanese beetles—helping to make the areas less attractive. Keeping trees and plants healthy also help as diseased plants and trees are particularly vulnerable to the beetles. Removing diseased or prematurely ripe fruit from trees or the ground will also prevent the beetles from coming to feed—thereby protecting the healthy fruit.
Japanese beetle trap buying guide
After the lure, you want to choose a trap that securely contains the beetles. Although most traps use replaceable plastic bags, the Tanglewood trap features a reusable plastic trap. Our top choices feature bags that have proven to be durable and reliable.
As far as pricing, the Tanglewood trap will have a higher initial cost. However, once you factor in the additional expense of purchasing replacement bags, the costs even out—and the reusable trap may prove to be more cost-effective overall.
The number of traps you need to purchase will depend on the size of the area you are trying to protect.
Tips for using Japanese beetle traps
Where to Place Japanese Beetle Traps
Hang the traps at the correct height—approximately 13 centimeters above the ground. This is the height at which the beetles fly, so it ensures they won’t miss the trap
- Place the traps as far away from the plants you are trying to protect. An optimum distance is 30 feet. If possible, place the traps next to a plant or tree (e.g., pine tree or boxwood tree) that isn’t attractive to the beetles
- Install the traps downwind from the plants you are protecting. Otherwise, you risk inadvertently causing the beetles to fly over the plants you are trying to protect while on their way to your trap—thereby diverting them to the plants instead of the trap
Tips for Making the Traps More Effective
- Place buckets of soapy water under the traps to capture beetles that don’t make it into the trap
- Another way to capture excess beetles attracted to traps is to place the traps near geraniums. Research has shown that Japanese beetles become paralyzed after feeding on geranium petals. According to the Agricultural Research Service (ARS), within 30 minutes of eating geranium petals, beetles rolled over on their backs and remained paralyzed for several hours. Although the beetles eventually recover, this gives you time to squish them, pick them up and put them in soapy water, or leave them to be eaten by predators. Savvy gardeners have begun using geraniums as “sacrificial” plants to protect their more treasured plants
- Place the traps as early in the season as possible to prevent the females from mating and laying eggs
Replace the bags (or empty and clean the trap) frequently so the smell of dead beetles doesn’t repel the living beetles you want to trap
- Because Japanese beetles can fly long distances, attempts to reduce the population are most effective when done throughout a community. Enlisting your neighbors into your efforts to trap and eliminate beetles will be more effective than going it on your own. Otherwise, your traps may simply attract the beetles that are emerging from your neighbor’s yard
Tips for Disposing of Dead Beetles
Are you wondering what to do with the dead beetles collected in your Japanese beetle bags? If you own chickens, they’ll love to eat them! You can also check with nearby farms to see if they are interested.
Putting the dead beetles in your compost bin is another option. Sealing them in plastic bags and tossing them in the trash is another alternative.
One creative gardener used the bags of dead beetles to protect her cherry tree. When her trap bag got full, she punched holes in it, pounded on it, and hung it on the tree. The smell of the dead beetles acted as a repellent. Of course, the downside to this method is the stinky smell of dead beetles, which may not be appreciated by everyone.
Useful information about Japanese beetles
Identifying Japanese Beetles
Knowing how to identify Japanese beetles is essential as people sometimes confuse them with other types of beetles. Japanese beetle traps will not work on different species of beetles or insects.
- Color: Metallic green body with iridescent coppery-brown wings. Rows of white hairs that resemble spots can be found on the sides of the abdomen
- Size: Adults range in size from 1/3 to 1/2 inches long and 1/4 inch wide. Males are usually smaller than females
Japanese Beetle Life Cycle
When trying to eliminate Japanese beetles, it is important to understand their life cycle. This is because most beetles stay near the area where they emerged from the ground. If there is a large amount of grubs in the soil, a massive infestation of adult beetles can be expected the following year, unless steps are taken to kill the grubs.
The beetle’s life cycle is approximately one year long and starts when the female beetle lays white, oval eggs in the soil about two to four inches deep. During each mating cycle, the female lays between one to five eggs. The mating cycle is repeated, and most females lay approximately forty to sixty eggs during her lifetime. Most of the egg laying happens during July and ends during the first week of August.
The eggs hatch in approximately ten days, at which point they turn into grubs. The grubs are shaped like the letter C and are cream-colored with brown heads and three pairs of legs. When mature, the grubs are about one inch long.
During August and early September, the grubs feed on the roots of grass, which can cause brown and blotchy patches in the grass. In the middle of October, the grubs move deeper into the soil—anywhere from six to eighteen inches deep—and remain inactive until the spring.
In late March or early April, the grubs wake up and move upward to feed on grass roots. In late May, the grubs cease feeding and being to pupate. Japanese beetle pupae are cream or reddish brown and are about a half inch long. Once they reach their full size, they emerge from the ground as adult beetles—usually in June. In warmer climates, emergence may take place earlier. Once Japanese beetle “season” begins, it lasts for about three months.
Assessing for Japanese Beetle Grubs
One way to find out whether you’ll be having a Japanese beetle problem is to survey your lawn for grubs. The best time to do this is in August. At this point, most of the eggs should have hatched, and the grubs will be about an inch long.
If you have brown or dead areas in your lawn, check that area for grubs. If grubs are found, this area of your yard should be treated. However, the density of grubs can vary widely in a small space.
- To survey for grubs, use this method and calculation provided by the USDA’s Managing the Japanese Beetle: A Homeowner’s Handbook
- Dig a square hole with a shovel that is approximately eight inches wide by eight inches long and three inches deep
- Flip the sod over onto a newspaper and search the grassroots and soil for grubs. Also, inspect the area around the hole you removed
- Record the number of grubs found in each location where you dig a hole
- To find out the number of grubs per square foot, multiply the number of grubs you found by 2.25. You should consider treating areas in your lawn with more than ten grubs per square foot
- Once you’re finished with the removed sod, put it back into the hole and add water to help it recover
If you need to treat your yard, you can choose between insecticides or biological control, which are briefly described above.