Chafer Grubs & Leatherjackets in UK Lawns – Identification, Treatment & Prevention
If your lawn is suddenly thinning, lifting easily, or being attacked by birds, the cause is often below the surface. In the UK, two of the most common causes of unexplained lawn decline are chafer grubs and leatherjackets (cranefly larvae). Both feed on grass roots, both can cause rapid damage, and both are frequently misdiagnosed as drought stress, nutrient deficiency or disease. Before applying fertiliser or overseeding, you need to confirm whether pests are present.
Step 1 – Inspect the Lawn Properly
A simple inspection usually confirms grub activity. Look for spongy areas underfoot, turf lifting easily like loose carpet, repeated bird pecking in the same patches, and sudden yellowing despite adequate watering. To check, cut a small square of turf approximately 10–15cm wide and gently lift it. Inspect the top 5–10cm of soil. If you see white, C-shaped larvae, chafer grubs are likely present. If you see thinner, brownish larvae with a leathery appearance and no obvious “C” shape, leatherjackets are more likely. Finding more than 5–10 larvae in a small section generally justifies treatment.
What Are Chafer Grubs?
Chafer grubs are the larvae of chafer beetles. Adult beetles lay eggs in late spring and early summer. The larvae hatch and begin feeding on grass roots beneath the surface. Damage typically becomes visible in late summer or early autumn. Turf may lift easily, brown patches can expand quickly, and bird activity often increases as predators search for larvae. If left untreated, damage can escalate rapidly.
What Are Leatherjackets?
Leatherjackets are the larvae of craneflies, often called daddy longlegs. Craneflies lay eggs in late summer. The larvae hatch and feed through autumn and winter. Damage is commonly more noticeable in late winter or early spring. Symptoms include thinning grass, weak root anchorage and patchy dieback. Because leatherjackets feed during cooler months, damage can appear gradual before worsening in spring.
How to Tell the Difference
Correct identification matters because treatment timing varies. Chafer grubs are white, thick-bodied and curl into a C-shape. Damage tends to peak in late summer and autumn. Leatherjackets are slimmer, brown or grey, and do not form a pronounced C-shape. Damage often peaks in late winter or spring. Both can attract significant bird activity, so physical inspection is more reliable than surface symptoms alone.
When to Treat (UK Timing Is Critical)
Biological control using nematodes is the most effective treatment available for domestic lawns. Timing is essential. Chafer grubs are best treated when larvae are young and near the surface, typically from July to September when soil temperatures are above approximately 12°C. Leatherjackets are usually treated in early autumn or spring while larvae are still small and soil temperatures are above roughly 10°C. Applying nematodes outside these temperature windows significantly reduces effectiveness. Specialist nematode treatments designed for UK chafer or leatherjacket control are widely available and must be applied according to supplier guidance.
How Severe Is the Damage?
Not every grub presence requires full renovation. The level of root loss determines the response.
A simple severity guide:
Mild damage
Small thinning patches
Grass still rooted firmly
Less than 5 larvae per inspection section
Minimal bird disturbance
In many cases, treatment alone is sufficient. Grass often recovers once feeding stops.
Moderate damage
Turf beginning to lift in sections
Noticeable thinning
5–15 larvae per inspection section
Increased bird activity
Treatment should be applied promptly. Light overseeding may be required once larvae are controlled.
Severe damage
Turf lifting extensively like carpet
Large brown or bare areas
More than 15 larvae per inspection section
Heavy bird disturbance
In these cases, treatment should be followed by structured renovation to restore density and root strength.
The earlier the problem is identified, the less disruptive recovery becomes.
Do You Need to Renovate After Pest Damage?
If damage is minor and caught early, grass often recovers naturally once feeding stops. However, if large areas have died back, root systems are severely compromised, or turf has lifted extensively, overseeding or structured renovation may be required. In many cases, pest treatment followed by a proper renovation produces the strongest recovery. For a full step-by-step framework, see the Complete UK Lawn Renovation Guide.
Prevention and Long-Term Lawn Health
While no lawn is completely immune, risk can be reduced by maintaining strong root growth, minimising excessive thatch, improving soil structure and aerating regularly. Weak, compacted or nutrient-poor lawns are more vulnerable to grub damage. A dense, healthy sward is the most effective long-term defence.
Frequently Asked Questions
How quickly do chafer grubs kill grass?
Chafer grubs can cause visible damage within a few weeks during late summer and early autumn. As they feed on grass roots, turf begins to loosen and brown patches expand. Damage often becomes noticeable when birds start pecking at the lawn to feed on the larvae. Early identification significantly reduces long-term impact.
Do nematodes really work for chafer grubs and leatherjackets?
Yes, when applied correctly. Nematodes are a biological treatment that infect and kill larvae underground. Their effectiveness depends heavily on timing and soil temperature. For best results, apply during the recommended treatment window and keep the soil consistently moist for at least two weeks after application.
Can my lawn recover without renovation?
In cases of mild damage, lawns often recover naturally once feeding stops, particularly if roots are still partially intact. However, moderate to severe damage usually requires overseeding to restore density. Where turf has lifted extensively, a structured lawn renovation produces stronger long-term results.
When is the best time to treat chafer grubs in the UK?
Chafer grubs are typically treated between July and September when larvae are small and near the surface and soil temperatures are above approximately 12°C. Leatherjackets are commonly treated in early autumn or spring when soil temperatures exceed roughly 10°C. Applying treatment outside these windows reduces effectiveness.
Why are birds attacking my lawn?
Birds are often attracted to lawns containing chafer grubs or leatherjackets. They can detect larvae beneath the surface and will repeatedly peck or pull back turf to feed. While bird damage looks severe, it is usually a symptom of an underlying grub problem rather than the primary issue.
