Japanese beetles are annoying pests that attack many types of plants. They feed on leaves, stems, flowers, buds, and roots.
Japanese beetles are attracted to light, so you can trap them with light traps. But where do Japanese beetles go at night?
I’ve found that Japanese beetles are most active around dusk and dawn. In fact, they prefer to move during the night because they’re less likely to get eaten by predators.
What is a Japanese Beetle?
A Japanese beetle is an invasive beetle of the scarab family. It was first discovered in America in the early 1900s after being accidentally introduced in the soil of imported plants.
Its scientific name is the Popillia japonica and it’s native to Japan. They can be seen feeding on trees, shrubs, grasses, flowers, and other vegetation.
Japanese beetles are highly destructive and are known to eat over 300 different plant species.
How to Identify the Japanese Beetle
The Japanese beetle bugs themselves are as pretty as they are destructive. Adult beetles measure approximately 1/3 to ½ inch long with a metallic green head and thorax. Its wings are copper-brown, and it has five white patches of hair on the sides of its abdomen and two on the tip of the abdomen.
Japanese beetle larvae are white to cream with a tan-colored head. They are C-shaped with legs that can be clearly seen. Unfortunately, they are pretty much indistinguishable from other white grubs.
The adult beetles skeletonize leaves by eating the leaf tissue between the major veins of leaves, causing them to have a tell-tale lace-like appearance.
What Do Japanese Beetles Eat?
Japanese beetles will feed on many types of plants.
The grubs live underground and mainly eat grass roots, causing the grass above it to die.
Adult Japanese Beetles eat the fruits, flowers, and leaves of fruit trees, such as apple, cherry, plum, and peach. They will also attack birch, linden, and elm, amongst others.
The adult beetles are partial to flowers such as rose, hollyhock, and marigold, as well as other fruits such as grape, raspberry, and currant. Herbs like basil are also targeted.
The beetles will eat overripe or wounded fruit, and regular harvesting can often limit their feeding on the edible parts of your plants.
Japanese beetles like to start at the top of a plant and eat downwards. Leaves that the beetles feed on emit an odor that will attract other beetles, so infestations are usually concentrated on one plant.
How Long Do Japanese Beetles Live?
Japanese beetles will live for 1 to 2 months. They spend most of their life-cycle underground in the grub stage.
The female lays her eggs underground in late summer, July and August. In about two weeks, the eggs hatch, and the larvae start to eat grass roots and other plant roots. The grubs grow throughout the rest of the summer, burrowing deeper into the earth once the soil cools in autumn.
In spring, the grubs move towards the surface, continue to eat, then pupate into adults. The adult beetle only lives for around one or two months, but they are extremely mobile and can travel several miles.
Females will lay multiple times, and each female can lay up to 60 eggs within her short lifespan.
Are Japanese Beetles Active During the Day?
Yes. Japanese beetles are most active during the day and usually feed from around 9 am to 3 pm. They prefer warm and sunny days. The are less active during cooler periods.
Adult beetles will not fly on rainy or windy days and seek shelter on cloudy days. However, dry soil can cause more eggs to die and result in fewer adults the following year.
Where Do Japanese Beetles Go at Night?
Japanese beetles actually return to their nests at night. These nests are usually just beneath the surface of the ground. They will choose a spot with a lot of cover so they can emerge from and enter their nest unseen.
If you are looking for Japanese beetle nests, check where there is thick foliage, grass, or other plant cover. The beetles make tiny entrance holes for their shallow nests, which you will be able to see beneath the plant cover.
Are Japanese Beetles Invasive?
Yes, this type of beetle species is highly invasive, and the USDA states that they are highly destructive and a threat to American agriculture.
Since first being detected in 1916, the beetles have spread to most of the states east of the Mississippi River, as well as those immediately to the west. Luckily, careful monitoring coupled with tough regulations stopped them from establishing further.
However, scientists now believe that climate change may impact the proliferation and distribution of Japanese Beetles. That means that this invasive species may be able to spread north to Canada.
How to Control the Japanese Beetle Population in Your Garden
Obviously, in these cases, prevention is better than cure. In Japan, the beetle’s natural enemies keep the population in check. But in the U.S., fewer predators and favorable conditions make it more of a pest.
You can purchase beneficial nematodes that will kill off Japanese beetle grubs. These nematodes are ideally applied to the soil in the spring before the grubs pupate, hatch. For this prevention method, you can also use Milky Spore to kill the grubs, it takes a year to establish, but the effects last for ten years.
The only problem is, you usually don’t know you have a Japanese beetle infestation until you see the beetles! The prevention method can be used as a long-term solution if you find a Japanese beetle or know it is prevalent in the area.
If the first you hear of the Japanese beetle is when these iridescent bugs are already munching on your roses, then there are a few things you can do to reduce their population.
First, you can use an insecticide. Pyrethrin-based insecticides are effective as a Japanese beetle killer and are a safe and effective way to control this pest. It also works on other harmful insects, including potato beetle, cabbageworm, flea beetles, and cucumber beetles.
If you want to go all-natural and organic, neem oil can be used as a spray. Neem oil works by reducing feeding, but it is best used in the very early stages of an attack. Neem oil also works for many other bugs, including lace bugs, sawflies, and aphids. You can also use a simple soapy water spray to knock the bugs off the plant.
If you have some time on your hands, you can hand-pick the bugs off affected plants. This method is easier in the morning when the beetles are more sluggish, but they are still slow enough to catch even at their most alert.
Chuck them in a bowl of soapy water, or if you have a fishpond, you can feed them to your koi! Although this method might sound tedious, it probably is the easiest and quickest solution.
Japanese beetle traps work by luring the male beetle into them before they can mate; however, these should be placed away from your plants as they might end up attracting more beetles!
If you don’t like the idea of killing the beetles, then row covers can keep them off your plants during peak feeding. You could also plant geraniums near any target plants.
The USDA reports that the beetles become paralyzed for several hours after consuming geraniums. While they recover eventually, you can rely on birds or other predators to do your dirty work, as the immobile beetles are sitting ducks to any other animal that wants to eat them.
How to Get Rid of Japanese Beetle
If you live in an area populated by Japanese beetles, you may not be able to get rid of them altogether. But by keeping a close eye on your plants and knowing the tell-tale signs, you can prevent Japanese beetle damage from being too widespread in your garden.
Japanese Beetles Final Thoughts
At night, Japanese beetles head home to their nest for sleep. Japanese beetles are not a huge threat to our gardens, but they can cause serious damage if left unchecked. If you notice any of the symptoms listed above, then it’s time to take action.
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