Curl Grub
Scarabaeidae
Curl grubs are C-shaped beetle larvae that chew turf and plant roots below the soil, causing patches of weak, dying grass.
Curl grub is the common name for the larval stage of scarab beetles (family Scarabaeidae), which includes African black beetle, Christmas beetles, and various cockchafers. Australia has many native and introduced scarab species, and several are considered lawn and garden pests in their grub stage.
The larva is a soft, plump, creamy-white to greyish grub with a distinct brown head capsule and three pairs of small legs near the front of the body. It curls into a tight C-shape when disturbed, which is where the common name comes from. Depending on species and age, grubs range from about 10mm up to 30-40mm long. They live in the soil beneath turf or garden beds, feeding on organic matter, thatch and plant roots. The adult beetles are stout, oval, dark brown to black or metallic beetles roughly 10-25mm long, active at night and often attracted to lights in warmer months.
Adult beetles lay eggs in soil over spring and summer. Eggs hatch into grubs that feed through summer and autumn, doing most root damage as they grow. Grubs are most active and cause the most visible damage during warm, moist conditions, then move deeper into the soil to overwinter before pupating and emerging as adults the following season.
Curl grubs are found across Australia in lawns, garden beds, pasture and turf. Populations build up in soils with plenty of organic matter and moisture, and damage is often worse in warm, humid regions or during warm, wet seasons. Management relies on monitoring grub numbers, maintaining healthy turf that can tolerate some root loss, and encouraging natural predators such as birds. Physical checks and targeted control measures are used when grub numbers exceed damaging thresholds.
How to identify
- Above-ground signs: Irregular patches of turf turn yellow, brown or wilt despite adequate water, and the grass often feels spongy or can be rolled back like carpet because the roots have been eaten away.
- Secondary damage: Birds, possums or foxes digging up the lawn at night are often searching for grubs, and this digging can cause as much visible damage as the grubs themselves.
- Confirming the pest: Cut a section of affected turf about 30cm square and peel it back to check the root zone and top few centimetres of soil. Finding several plump, C-shaped white to grey grubs with brown heads confirms curl grub activity. Counting grubs per square metre helps judge whether the population is high enough to be causing real damage.
- Lookalikes: Curl grubs are sometimes confused with other soil-dwelling larvae such as wireworms, which are thin, hard-bodied and yellow-brown rather than plump and C-shaped. Damage from curl grubs can also resemble drought stress, so checking the soil and roots directly is the only reliable way to confirm the cause.
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