Curl grub (scarab beetle larvae)
Scarabaeidae spp. (includes African black beetle and Christmas beetle larvae)
A fat, creamy grub that curls into a C and eats roots. Look under a dead patch of lawn next to a bed.
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Identify from a photoBackground
Curl grub is the common name for the larval stage of several scarab beetles found across Australian gardens, most often African black beetle and Christmas beetle. The grub curls into a tight C-shape when disturbed, which is the easiest way to tell it apart from a caterpillar, which stays straighter and has visible legs down most of its body.
The grubs live below the surface and feed on plant roots, including grass roots and the roots of vegetable seedlings. Damage is usually noticed above ground first: a section of lawn that has gone brown and can be rolled back like carpet because the roots holding it down have been eaten away, or a row of seedlings that wilts and dies for no obvious reason even though the soil is moist.
Adult beetles emerge in late spring and summer, feed on leaves at night, then lay eggs back into the soil, so grub numbers usually build through summer and peak in autumn before the largest grubs pupate over winter.
How to identify
- C-shaped, cream to white grub, 10 to 40mm long depending on species and age, with a distinct brown head capsule and six small legs near the head.
- Found a few centimetres below the soil or turf surface, curled up, not moving quickly when exposed.
- Lawn or bed can be lifted or rolled back like a loose carpet because the root mat has been eaten through.
- Seedlings and young transplants wilt, yellow, or fall over even with adequate water, because the roots are damaged.
- Increased bird, possum or cane toad activity digging at the lawn at night, hunting the grubs.
Life cycle
One generation a year in most of eastern Australia. Adult beetles fly and mate in late spring to early summer, lay eggs in soil through summer, grubs feed and grow through summer and autumn, then move deeper and pupate over winter before emerging as adults the following spring.
Weather triggers
- Temperature: 18-32°C
- Humidity: >50%
- Grubs feed closest to the surface, and do the most visible damage, in warm, moist soil. Heavy watering or a wet spell right before a hot stretch tends to bring numbers to the surface.
Peak season (southern hemisphere)
Red = active season · Dark red outlined = this month
Affected vegetables & crops
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Climate zones at risk
Organic & low-impact control
- Water the suspect area, lay a wet hessian sack or damp cardboard over it overnight, then check underneath at dawn; grubs and adult beetles often gather there and can be collected by hand.
- Apply a garden-grade beneficial (entomopathogenic) nematode product to moist soil in late summer to early autumn while grubs are still small and near the surface.
- Turn over and expose soil in a heavily affected bed in autumn or winter so birds can find and eat the grubs.
- Keep lawn and garden beds on the lean side of watering; grubs thrive in consistently moist soil.
Chemical control
- A registered lawn grub granule or liquid treatment applied and watered in during late summer to early autumn, when grubs are smallest and most vulnerable, following the label rate exactly.
- Spot-treat only the affected area rather than the whole garden; scarab larvae are not usually evenly spread.
Always read product labels. Registrations change.
Prevention
- Keep an eye on lawn areas next to vegetable beds in late summer and autumn; treating a lawn infestation early stops grubs spreading into adjoining beds.
- Avoid overwatering. Deep, less frequent watering keeps soil less attractive to egg-laying beetles than a lawn kept constantly damp.
- Mulch vegetable beds to keep soil temperature more even; scarab beetles favour bare, warm soil for egg laying.
Sources
- Queensland Department of Agriculture and Fisheries, home garden lawn grub and scarab pest advice
- NSW Department of Primary Industries, scarab beetle pests of turf and pasture
- Agriculture Victoria, African black beetle
Accuracy confidence: medium. We update this library as new extension guidance is published.
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