Grub Worm: How to Tell If You Have Them, and When to Treat

Most lawns carry grubs harmlessly. The threshold is 6 to 10 per square foot — how to count them, and why timing matters more than the product.

By Zakaria September 18, 2026 5 min read Save to Pinterest

Two cream-white C-shaped chafer grubs on dark soil, showing brown head capsules and three pairs of legs — Photo: Сарапулов, CC BY 4.0, via Wikimedia Commons

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Almost every lawn has grubs. Almost none of them need treating. The number that matters is 6 to 10 per square foot — and finding that out takes five minutes with a spade.

The short answer

Grub worms are the larvae of scarab beetles — Japanese beetles, June beetles and chafers — living in the top few inches of soil and eating grass roots. They are C-shaped, cream-white, with a brown head and three pairs of legs. Most lawns carry them harmlessly: the damage threshold is roughly 6 to 10 per square foot, measured by peeling back a one-foot square of turf and counting. Treat only above that. Timing decides whether treatment works — preventive products go down in early summer before eggs hatch, curative ones in late summer while grubs are small, and spring treatment is largely wasted.

Under 6 per square foot is normal. Do nothing
Peel back a 1 ft square of turf and count. Five minutes
Early summer = preventive. Late summer = curative. Spring is wasted
Animal digging is often the real damage
Routine annual treatment is the common mistake

What they actually are

Not worms. The larvae of scarab beetles, and which beetle depends on where you are.

C-shaped, curling when disturbed
Cream-white, soft-bodied, ½ to 1½ inches
Brown or orange head capsule
Three pairs of legs at the front end
Living in the top 1 to 3 inches of soil, eating grass roots

Who you are dealing with

Beetle	Life cycle	Where
Japanese beetle	1 year	Eastern and midwestern US; spreading
Masked chafer	1 year	Much of the US
European chafer	1 year	Northeast US, southern Canada, UK
June beetle / May beetle	2–3 years	Widespread
Green June beetle	1 year	Southeast US

The multi-year species matter because a single treatment cannot line up with every stage at once, and populations do not collapse the way an annual species can.

Do not confuse them with earthworms or billbugs

Earthworms are pink-brown, segmented, legless and move by stretching. They are pure benefit and should never be treated against.

Billbug larvae are similar in colour to grubs but are legless and much smaller, and they need a different response. If what you found has no legs, it is not a grub.

The count that decides everything

Do this before buying anything.

Pick a suspect patch, at the edge of damage rather than the dead centre — grubs have already left fully dead turf.
Cut a one-foot square on three sides with a spade, 3 inches deep.
Peel it back like a flap.
Count grubs in the soil and in the root mat.
Repeat in three or four spots, including healthy lawn. They are very patchy.
Fold the turf back, tread it down, water it.

What the count means

Grubs per sq ft	What to do
0–5	Nothing. This is a normal, healthy lawn
6–9	Borderline. Treat only if the lawn is already stressed or has thin roots
10+	Treatment justified in a healthy lawn
5+ in drought-stressed turf	Treat — a weak lawn cannot outgrow the damage

Reading the damage

Grub damage:

Irregular brown patches that do not respond to watering
Turf lifts like loose carpet — the roots have gone
Spongy underfoot
Worst in late summer and early autumn

Not grub damage: drought, dog urine, fungal disease, chinch bugs, compaction and fertiliser burn all produce brown patches. Only the peel-back test distinguishes them, and turf that does not lift freely has roots, so the problem is something else.

The animals often do more damage than the grubs

Skunks, raccoons, crows, badgers and moles dig lawns up to eat grubs, and a night of that does far more visible harm than the grubs themselves. It is also the most common way people discover they have grubs at all.

Treating the grubs removes the reason for the digging — but it takes weeks, so it is not an answer to tonight’s damage.

Timing, which matters more than the product

This is where most treatments fail. Grub products are not interchangeable, and each works on a specific stage.

When to apply what

Window	Type	Works because
Early summer (roughly June–mid July)	Preventive	Goes down before eggs hatch; kills tiny new grubs
Late summer–early autumn	Curative	Grubs are still small and feeding near the surface
Spring	Mostly wasted	Grubs are large, nearly finished feeding, about to pupate
Midwinter	Nothing	They are deep and dormant

Two rules that apply whichever you use:

Water it in. These products have to reach the root zone, and an unwatered application sits on the thatch doing nothing.
Read the label for your product and region. Timings shift with latitude, and several older active ingredients are now restricted.

Options, from least to most drastic

1. Do nothing. Genuinely the right answer below the threshold.

2. Fix the lawn instead. A deep-rooted lawn tolerates grubs that would wreck a weak one.

Water deeply and infrequently — roots follow water down
Mow high, 3 to 4 inches. Taller grass, deeper roots
Reduce thatch, where beetles prefer to lay
Let it go dormant in high summer if you can: dry soil in the egg-laying window kills many eggs outright

3. Beneficial nematodes — Heterorhabditis bacteriophora specifically, not the other species.

Apply in the evening or on a dull day; UV kills them
Water in immediately, and keep the soil damp for two weeks
Buy fresh, cold-stored stock and use it promptly
Soil above about 12°C

Most “nematodes did nothing” reports come down to heat, sunlight or dry ground, not the nematodes.

4. Milky spore. Only affects Japanese beetle grubs, takes several years to establish, and does nothing about chafers. Worth it only for a long-term Japanese beetle problem.

5. Insecticide, if the count genuinely justifies it. Treat only the affected area rather than the whole lawn, follow the label exactly, and never apply to flowering weeds in the lawn — clover and dandelion in a treated lawn kill bees.

The annual preventive habit is the thing to break

Blanket-treating every year is the most common mistake with grubs. In most years the population is below the damage threshold, so the treatment achieves nothing visible while killing earthworms, ground beetles, and pollinators using lawn flowers.

Count first. Treat the area, not the lawn. Skip years when the count is low.

Common questions

What is a grub worm?

The larval stage of scarab beetles — Japanese beetles, June beetles, chafers and masked chafers, depending on region. They are C-shaped, cream-white, soft-bodied, with a brown head and three pairs of legs at the front end, and they live in the top few inches of soil eating grass roots. They are not worms at all, and the distinction matters because earthworms in the same soil are beneficial and look nothing like them once you know what to look for.

How do I know if I have a grub problem?

Cut a one-foot square of turf on three sides and peel it back like a flap, then count the grubs in the top few inches of soil. Fewer than six per square foot is normal and needs nothing. Six to ten is borderline and depends on how stressed the lawn is. More than ten in a healthy lawn, or more than five in a drought-stressed one, is worth treating. Do this in several places, because grubs are patchy.

What are the signs of grubs in a lawn?

Irregular brown patches that do not green up after watering, turf that lifts like loose carpet because the roots have been eaten away, spongy ground underfoot, and a sudden increase in skunks, raccoons, moles or crows digging the lawn up at night. The animal damage is often worse than the grub damage and is usually what makes people investigate. Drought damage looks similar, so the peel-back test is what settles it.

When should I apply grub control?

Timing matters more than which product you choose. Preventive treatments go down in early summer, roughly June to mid July in most of the northern United States, before eggs hatch — they work on tiny new grubs and do nothing to large ones. Curative treatments go down in late summer to early autumn while grubs are still small and near the surface. Treating in spring is largely wasted: the grubs are big, nearly done feeding, and about to pupate anyway.

Do beneficial nematodes work on grubs?

Yes, when handled properly, and Heterorhabditis bacteriophora is the species to use for grubs. They are living organisms, so they die in sunlight and in dry soil — apply in the evening or on a dull day, water them in immediately, keep the soil damp for a fortnight, and buy fresh stock that has been kept cold. Most reports of nematodes not working trace back to a packet left in a hot car or applied to dry ground in full sun.

Should I treat my lawn for grubs every year?

No. Routine annual preventive treatment is the most common mistake here — it applies insecticide to a lawn that in most years has grub numbers below the damage threshold, and it kills earthworms, ground beetles and pollinators visiting lawn flowers along with the target. Count first, treat only when the count justifies it, and keep the lawn healthy enough to tolerate a normal population.

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A newly seeded lawn on the left beside established turf on the right

Lawn & Soil · Sep 8, 2026