Lawn Insects That Damage Your Grass: Army Worm and African Black Beetle Explained
Spring in Lake Macquarie and the northern Central Coast brings warmer soil, faster grass growth, and longer days — but it also brings the insects that can undo months of careful lawn maintenance almost overnight. Two of the most damaging are army worm and African black beetle. If you've noticed brown patches appearing suddenly across your lawn, or sections of turf that lift away from the soil with barely any effort, one of these pests is likely the culprit.
Here's what you need to know about each one.
Army Worm
What Is Army Worm?
Army worm is not actually a worm — it's the larval stage of a moth. The caterpillars are typically olive-green to brown with pale stripes running along the body, and they feed by chewing grass blades down at or near the surface. The name comes from the way they move: in large numbers, stripping a section of lawn before advancing to the next. This is why the damage can appear so fast. A lawn that looked perfectly fine on a Tuesday evening can have a badly browned patch by Wednesday morning, because army worm feeds heavily after dark.
In the Lake Macquarie and Central Coast region, army worm is most active through spring and into summer, with numbers often spiking after a period of warm, humid weather — exactly the conditions that arrive in September.
How to Identify Army Worm Damage
The most obvious sign is brown or straw-coloured patches that seem to appear from nowhere. Part the grass at the edge of the affected area and look at the base — you may find the caterpillars themselves, or small dark pellet-like droppings. Birds are another indicator: mynas, magpies and currawongs will peck persistently at areas where army worm is feeding below the surface.
A simple test is to mix a small amount of dish soap in a bucket of water and pour it over a suspicious patch. If army worm is present, they'll surface within a few minutes.
Treatment
A contact insecticide is the most effective solution for army worm. Products containing bifenthrin are widely available at hardware and garden stores and work quickly on surface-feeding caterpillars. For longer-lasting protection, Acelepryn (chlorantraniliprole) is a professional-grade option that offers up to six months of residual control — it's what we use and is available online and through turf suppliers.
Apply any treatment in the late afternoon or early evening when army worm is most active, and lightly water in afterwards if the label allows. A second application may be needed if moth activity in the area is high.
Prevention
The best defence against army worm is a healthy, dense lawn. Thick turf is harder to damage significantly and recovers faster when pests do get in. Regular mowing, seasonal fertilising, and consistent watering all help build resilience. Monitoring through spring and summer is just as important — check your lawn after warm, wet periods and deal with any signs of activity early. A small patch treated quickly is far easier to manage than widespread damage that's been allowed to spread.
African Black Beetle
What Is African Black Beetle?
African black beetle (Heteronychus arator) causes a different kind of damage, and it does it in two stages.
The adult beetle is a hard-shelled, shiny black insect about 12–15mm long. It damages lawns by chewing through grass stems at ground level, killing individual plants and creating irregular dead patches across the surface. The larvae are small, C-shaped white curl grubs that live in the soil and feed on grass roots from below. Root damage is often the more serious of the two — once the root system is gone, affected grass loses its ability to take up water and nutrients, and the turf will pull up from the soil like a loose mat.
Spring is the most damaging period because adult beetles are emerging from the soil while the previous season's grubs are still active underground. Both stages can be causing damage at the same time.
How to Identify African Black Beetle Damage
Look for brown patches that don't recover with watering — that's the key difference from drought stress. Try grabbing a handful of affected turf and pulling gently. If it lifts away with almost no resistance and you can see the root zone has been eaten back, grubs are almost certainly the cause. Digging into the soil in a damaged area and finding white curl grubs a few centimetres down confirms it. Adult beetle damage tends to look more patchy and scattered, with individual grass plants dying rather than large continuous dead zones.
The soapy water test works here too — pour a diluted dish soap solution over a suspected area and watch for grubs or adult beetles coming to the surface.
Treatment
Treatment depends on which stage you're dealing with. For adult beetles at the surface, a contact insecticide containing bifenthrin applied to the lawn and watered in will work. For curl grubs in the soil, a systemic product like Acelepryn is more effective — it gets down into the root zone where the grubs are feeding and provides extended protection through the season.
Always follow the product label; the timing and rate of application make a real difference to the result. Bifenthrin and Acelepryn are the products we use professionally at ALTA Garden Care. If you'd prefer not to handle pesticide application yourself, or the damage is already across a significant area, get in touch and we can take care of it.
Prevention
A healthy, well-maintained lawn is your best protection. Avoid overwatering — African black beetle is attracted to consistently moist soil conditions, so good watering habits reduce the risk. Regular dethatching helps too, as excessive thatch buildup creates a favourable environment for beetles to lay eggs. As with army worm, keeping an eye on your lawn through the warmer months and catching any signs of damage early makes treatment far simpler.
Need Help Getting Your Lawn Back on Track?
If your lawn has taken a hit from army worm or African black beetle this spring, ALTA Garden Care can help. Regular maintenance — mowing, seasonal fertilising, and keeping an eye on things visit to visit — is the most effective way to build a lawn that recovers quickly from pest damage and stays healthier long-term.
If you're in Cooranbong, Morisset, Dora Creek, Bonnells Bay, Halekulani, Mardi, Magenta, Sunshine or surrounding areas and want someone reliable to take care of your lawn, get in touch for a free quote.
ALTA Garden Care provides regular lawn and garden maintenance for homeowners across Cooranbong, Morisset, Dora Creek, Bonnells Bay, Halekulani, Mardi, Magenta, Sunshine and surrounding areas.