Have you been finding patches of yellowed or dead grass on your lawn? It could be the work of the notorious lawn killer, the white grub. White grubs are the larval form of scarab beetles. Beetles in the scarab family are comprised of thirty thousand different species around the world. In Florida, the most common scarab beetles are June Bugs, Japanese Beetles, Rainbow Scarabs, and the Green June Bug. The immature form of these beetles (larva) feeds on the roots of grasses, ornamental plants, and food crops. The feeding habits of these immature beetles will cause sections of the lawn to turn brown and die.
Grubs, or beetle larvae, sit relatively shallow under the surface in a c-shaped semicircle. They are milky white with a brown head and six spindly legs. Some species, like the Japanese beetle, can grow to be about one to two inches in length before maturity as an adult beetle. Still, most are about the size of a quarter. White grubs are often mistaken for worms. However, these are not worms at all, but the immature form of a family of beetles called Scarabaeidae. The larvae eat the roots of grasses, ornamental plants, and food crops. Just one species, the Japanese beetle, accounts for nearly $45 million annually in pest management in the United States. The Japanese beetle is considered the most destructive of all beetles that plague the US.
You may already be familiar with scarab beetles, as these were the beetles worshipped by the Ancient Egyptian culture. These beetles symbolized the restoration of life in this society. The distinct oval shape and bright colors of scarab beetles often inspired designs for good luck charms and other jewelry. Scarabs were commonly used in funeral art, providing the deceased guidance and certainty in their resurrection. It is easier to comprehend why the Egyptians worshipped these beetles as a sign of rebirth if you understand more about the lifecycle of this family of beetles.
Lifecycle of a Scarab Beetle
Scarab beetles lay their eggs in the late summer, which for most species, takes about two weeks for the grubs to hatch. The grubs then feed on the roots of grasses and other organic matter for the next few months. In the late fall, the grubs go dormant for the winter. Early the following spring, the grubs will wake and begin feeding again. Just before summer, the grubs will pupate and emerge from the ground as adult beetles. This emergence from seemingly nowhere is why the Egyptians associated scarab beetles (specifically the dung beetle) with rebirth and renewal.
Why do they destroy your lawn?
Unlike earthworms, which actually help your lawn by aerating the soil, grubs are lawn killers because they eat the roots turning an otherwise healthy lawn into patches of dead and dying grass. This feeding leaves unsightly yellow or brown spots on your beautifully manicured lawn. This destruction resembles that of a drought-stricken lawn, which makes grubs hard to identify from the surface, without further inspection. The other issue with grubs is that they attract moles, which can make an even worse mess of your lawn. Moles are grub hunters, so if you know you have moles, you can bet you probably also have a grub problem.
How to tell if you have grubs?
Does your lawn feel a bit spongy after a proper watering? That could be a sign that grubs are wreaking havoc on the roots of your grass. Lots of birds in your yard may also be an indicator of grubs. However, neither of these is a sure method. Birds dig for all sorts of underground goodies. Still, there are a few species of birds that prefer grubs to other subterranean dwellers, including starlings, crows, robins, cardinals, and blue jays. If you notice flocks of birds having a feast in your yard day after day, then you might be alerted to a grub issue. If it is just a few here and there, it is not a significant enough problem to seek alternative solutions. Just let the birds do their job in the cycle of life.
If you are sensing you have a more significant issue than just a few random grubs, then determining if you have an infestation is quite simple. The first sign of a lawn that may have grubs is the notorious yellow patches of dying grass. If you have been plagued by beetles in the past, you can be reasonably sure they’ve laid their eggs nearby, and more will emerge in the spring. You can check your lawn to find out if it is being affected by grubs, or if it is just a lack of watering by cutting around the edge of a yellow patch. Go down about one inch deep and peel back the spot. If the area of grass rolls back like a carpet, then you know that the roots are destroyed by the handiwork of grubs. Obviously, if you peel back the area and see the larvae, then you have identified your problem.
On the other hand, if your lawn peels back but gives resistance, then your roots are intact. Implementing a better watering schedule may help you return your lawn to its green glory. Grub infestations are considered severe if you see more than five grubs per square foot, which is regarded as a significant enough problem to call in the experts. Failure to treat can cause considerable damage to your lawn. Grub issues are typically handled by your lawn care experts.
How to Treat for Grubs
There are some DIY options if you prefer to take care of the problem yourself. Be forewarned, however, that using harsh chemicals on your lawn could be detrimental to the grass itself. Many broad-spectrum chemicals will kill off beneficial insects, like earthworms and bees, that help your lawn grow. If you do have grubs, then the process is a bit more difficult to control using safer methods. Start by determining the extent of the problem. For low to moderate infestation, nematodes are one of the best options for attacking white grubs. An added benefit to these microscopic soil worms is that they also attack flea larvae that may also be hidden in your lawn. Nematodes can be purchased from your local nursery or Amazon. Nematodes do require being watered into the ground. They also need a moist environment to do their job adequately, so multiple watering sessions will be required. All the big brands sell nematode mixtures, but the pure nematode products work just as well.
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If your infestation is more substantial than these remedies will offer, you should call in your local pest control expert for advice. Your lawn care specialist can also help you treat the problem.
How to Prevent Grubs from Returning
Attracting beneficial birds to your yard will help keep small grub populations under control. Cardinals, starlings, and robins eat both the larva and adult beetles, so put out a few bird feeders and fill it with your favorite songbird seed. Consider also adding a birdbath and some birdhouses. The more bird-friendly your yard, the more your lawn will thank you. Plus, you will get the added benefit of hearing them sing.
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Managing your lawn correctly can reduce your risk of grubs getting out of control. Mowing your lawn no shorter than 2” will deter beetles from laying eggs as they prefer shorter landscapes for this activity. Consistently watering your lawn will help deter scarab beetles from laying their eggs. Keeping your grass at optimal moisture levels promotes microbial activity. Thus attracting other beneficial insects that feed on grubs such as ants, ground beetles, and wasps. The most important thing to remember when dealing with Japanese beetle grubs is not to use lures to attempt to trap them unless you are dealing with multiple acres. You can actually attract beetles from up to five hundred yards away with these traps, causing a worse infestation the following year.
How To Identify Common Scarab Beetles
Japanese Beetle: Approximately 3/8” long, green head, reddish-tan wings, and an overall “shiny” appearance. They have twelve distinctive white hairs running along their bodies, five down each side, and two on the rear.
May/June Bug: Approximately ½” long, less oval than most scarabs with a more elongated shape. Mostly reddish-brown to black coloration. Glossy appearance.
Rainbow Scarab (Dung Beetle): Approximately ¾” in length, oval-shaped with metallic green or blue-green coloring with a distinctive copper coloring above the wings. Few specimens are dark blue to black and do not have the copper coloration. The most notable feature of the Rainbow Scarab is the distinctive horn on its head.
Green June Bug: Approximately ½”-1” long, with squared oval shape. Metallic green coloration with yellow to rust-colored striations along the edge of the wings.
Once you have identified which of the scarab beetles you are dealing with, you can better prepare yourself and your lawn for preventing future infestations.
Grubs are an excellent source of protein, calcium, and minerals. Would you eat one?
Woodruff, Robert E. The Scarab Beetles of Florida. Florida Division of Plant Industry (PALMM), 1973
UF|IFAS Gardening Solutions
UF|IFAS Department of Entomology & Nemotology
True White Grub:
Editors of Encyclopedia Britannica, et al. “June Beetle” “Scarab Beetle” “Chafer Beetle” “Dung Beetle” “Japanese Beetle” Encyclopedia Britannica, Encyclopedia Britannica, Inc., 2020