White grubs are the larval stage of scarab beetles, and they follow a four-stage life cycle: egg, larva, pupa, and adult. Most species complete this cycle in a single year, though the timing of each stage determines when your lawn is most vulnerable to damage and when treatment is most effective.
The Four Stages of Development
Like all beetles, white grubs undergo complete metamorphosis, meaning they pass through four distinct forms rather than gradually growing into adults.
Eggs: Adult female beetles deposit small, shiny, white, oval-shaped eggs in moist soil during early to mid-summer. As the embryo develops, the eggs absorb moisture from the surrounding soil and expand into spheres. This stage lasts roughly two weeks, depending on soil temperature and moisture.
Larvae (grubs): This is the stage that causes lawn damage. Newly hatched grubs are plump, pale, C-shaped creatures with six true legs near the head and no leg-like structures along the abdomen (which distinguishes them from caterpillars). They feed on grass roots in the thatch layer just below the soil surface, growing through three size stages called instars. By the final instar, their chewing mouthparts are highly developed and they’re capable of serious root destruction. The larval stage is by far the longest part of the life cycle, lasting from midsummer through fall, then resuming after winter.
Pupae: In late spring, mature larvae stop feeding and transform into pupae in the soil. During this resting phase, the grub’s body reorganizes into its adult beetle form. Pupation lasts a few weeks.
Adults: After pupating, grubs emerge as stout-bodied, short-lived beetles. Different species look quite different as adults, varying in color and size, but they share the same basic body plan. Adults mate, females lay eggs in the soil, and the cycle begins again.
Seasonal Timeline Through the Year
For the most common species (Japanese beetles, masked chafers, and others with one-year life cycles), the calendar breaks down like this. Adults emerge and mate in early summer, typically June or July. Females burrow into moist soil to lay eggs, often favoring well-watered lawns. Eggs hatch within a couple of weeks, and tiny first-instar grubs begin feeding on grass roots immediately.
Through late summer and into fall, grubs grow rapidly. This is when lawn damage becomes most visible, usually peaking in August and September. As soil temperatures drop in late fall, grubs stop feeding and burrow deeper into the ground to overwinter, sometimes reaching 8 to 12 inches below the surface.
When the soil warms again in spring, grubs migrate back toward the surface and resume feeding on roots for a few weeks. By late May, they stop eating and pupate. New adults emerge in June or July, and the cycle repeats.
One notable exception: May and June beetles take two to three years to complete their life cycle, spending multiple seasons as larvae in the soil. On the other end of the spectrum, black turfgrass ataenius beetles can produce two generations per year.
How Grub Damage Shows Up in Your Lawn
Grubs chew off grass roots just below the soil surface, which cripples the turf’s ability to absorb water and nutrients. The damage compounds during hot, dry weather when grass is already stressed. Early signs include gradual thinning, yellowing, and weakening of the grass, followed by scattered, irregular dead patches. As feeding continues, those patches expand, and areas that looked healthy can suddenly wilt.
Two physical tests help confirm the problem. First, infested turf often feels spongy underfoot. Second, heavily damaged sod pulls loose from the soil like lifting a carpet, because the roots anchoring it have been eaten away. You may also notice skunks, raccoons, or armadillos digging up sections of your lawn to feed on grubs. Sometimes this animal damage is worse than what the grubs themselves cause.
How Many Grubs Are Too Many
Not every grub in your soil is a problem. Healthy, well-maintained turf can tolerate a surprising number. The general treatment threshold is 5 to 10 grubs per square foot, though the exact number depends on the species and the condition of your lawn.
Japanese beetle grubs become a concern at about 6 to 8 per square foot in healthy turf, and up to 10 per square foot if the grass is in excellent shape. Southern masked chafer grubs are less damaging, with well-managed lawns tolerating up to 20 per square foot. May and June beetle grubs are more destructive: populations above 7 per square foot can wipe out roots entirely, so treatment is typically warranted at 4 to 5. Green June beetle grubs don’t actually feed on grass roots at all, but their tunneling causes problems above 5 to 7 per square foot.
To check your lawn, cut a one-foot-square section of sod about 3 inches deep with a shovel, peel it back, and count the grubs you see in the soil and on the underside of the sod. Check several spots, since grub populations are rarely uniform across a lawn.
Timing Treatment to the Life Cycle
Understanding the life cycle is essential for choosing the right control strategy, because different products work at different stages.
Preventive Products
Preventive insecticides target newly hatched, small grubs and must be in the soil before or shortly after eggs hatch. Most preventive products work best when applied in June or July, timed to be active when tiny first-instar grubs begin feeding. One exception is chlorantraniliprole, which is less water soluble and can be applied earlier, from April through mid-July. Research from Michigan State University has shown that earlier applications of this product (before June) actually perform better than later ones.
Preventive products do not work on large, mature grubs. Applying them in fall or spring is ineffective.
Curative Products
If you discover a heavy infestation in fall or early spring, curative insecticides are the remaining option. These are short-lived compounds that kill grubs of all sizes. The critical timing detail: do not apply curative products in spring after mid-May, because grubs stop feeding in late May as they prepare to pupate. A grub that isn’t eating won’t ingest the treatment.
Biological Controls
Several biological options exist, including beneficial nematodes and bacterial products marketed as “milky spore.” However, university research has consistently found that these biological products provide limited and highly variable control compared to chemical options. Milky spore in particular has not performed well in recent university trials. If you choose a biological approach, follow the product label closely for soil temperature and moisture requirements, and set expectations that results may be inconsistent.
Why Life Cycle Knowledge Matters
The single most common mistake homeowners make with grub control is applying the wrong product at the wrong time. Preventive products applied in September won’t touch the large grubs already feeding. Curative products applied in June are unnecessary when grubs haven’t hatched yet. And any treatment applied during pupation in late May or June is essentially wasted, since the grubs are inactive and not feeding.
Matching your response to the grub’s current life stage, whether that means a preventive application in early summer, a curative treatment in early fall, or simply accepting that a low population doesn’t need treatment at all, is the difference between effective management and throwing money at your lawn.