A white grub is the larval stage of a scarab beetle, the thick, C-shaped creature you find curled up in soil when digging in your yard. These larvae are creamy white with a dark brown head and three pairs of legs near the front of their body. They live underground and feed on grass roots, making them one of the most common and destructive lawn pests in North America.
Which Beetles Produce White Grubs
Several species of scarab beetle start life as white grubs, and they all look remarkably similar at first glance. The most common culprits in North American lawns are May or June beetles, masked chafers, and Japanese beetles. May or June beetles are the largest of the group as adults, with oblong, robust brown bodies. Masked chafers are smaller and yellowish brown. Japanese beetles are easy to spot as adults because of their metallic green bodies and bronze wing covers, but their larvae look nearly identical to the others underground.
Other species that show up in lawns include European chafers, Asiatic garden beetles, oriental beetles, and a smaller species called the black turfgrass ataenius. The only reliable way to tell grub species apart is by flipping the larva over and examining the pattern of tiny bristles on the underside of its tail end, called the raster pattern. You need at least a 10x magnifying lens to see it clearly, and for smaller species, a microscope helps. Identifying the species matters because it determines when and how you should treat them.
How White Grubs Damage Your Lawn
White grubs feed on turfgrass roots just below the soil surface. The damage shows up as irregular patches of dead or dying grass that look drought-stressed, even when the lawn has had plenty of water. In severe cases, the root system is so destroyed that you can grab the turf and roll it back like a carpet.
To check whether grubs are the problem, cut a small square of turf at the edge of a brown patch and peel it back. If the grass pulls up easily with almost no roots attached and you see white, curled larvae in the soil, you’ve found your answer. Five or more grubs per square foot is generally the point where treatment becomes worthwhile. At lower numbers, a healthy lawn can usually tolerate them without visible damage.
Secondary Damage From Wildlife
Grubs attract hungry animals. Skunks hunt at night, poking small, nose-sized holes in the lawn as they root for larvae. Raccoons are more destructive: they use their front paws to grab and flip entire pieces of sod, peeling back turf to get at the grubs underneath. This is especially common on newly laid sod or lawns with shallow root systems. You might even notice a skunk odor in your yard if a raccoon disturbs a skunk while both are feeding in the same area. If you’re waking up to torn-up turf, the grubs themselves may be doing less damage than the animals hunting them.
Preventing Grub Problems
One of the simplest defenses is mowing your lawn at 3 inches or higher. Taller grass develops a larger root system that can tolerate more grub feeding before showing damage. Combined with moderate fertilization and watering during dry spells, raising your mowing height can reduce or eliminate the need for any insecticide. Mowing below 3 inches actually stresses the turf and makes it more vulnerable.
Preventive insecticide products are designed to be applied before grubs hatch or while they’re still very small. The timing depends on the product. Chlorantraniliprole, sold to homeowners as GrubEx, works best when applied between mid-April and early June. Neonicotinoid-based products should go down between mid-June and early August, timed to when adult beetles are laying eggs and the active ingredient can reach newly hatched larvae. These products need to be watered into the soil after application to reach the root zone where grubs feed.
Treating an Active Infestation
If grubs are already large and causing visible damage in late summer, your options narrow. Curative products work on contact but are less effective as grubs grow. One common curative ingredient, trichlorfon, kills grubs within one to three days and breaks down in the soil within seven to ten days. Another option, carbaryl, also provides quick knockdown. But once grubs reach full size, often by mid-September, even these curative treatments rarely reduce the population by more than 50%. The window for effective treatment closes as fall progresses.
Biological Alternatives
For homeowners who want to avoid synthetic insecticides, two biological options target grubs in the soil. Milky spore disease is a naturally occurring bacterium that specifically infects Japanese beetle grubs. Once established, it can remain active in the soil for 15 years or longer. The catch is that it takes two to four years to fully colonize the treated area, especially in colder climates, and it only works on Japanese beetle larvae, not other grub species.
Beneficial nematodes are microscopic worms that parasitize grubs. Different nematode species hunt in different ways. Some ambush prey near the soil surface, while others actively track grubs deeper in the soil by following chemical trails the larvae leave behind. The hunting species tend to be more effective against grubs because the larvae feed several inches below the surface. Nematodes work against multiple grub species but need moist soil and moderate temperatures to survive after application.