A lawn that turns yellow in patches, or is ripped up overnight, often points to grubs feeding on the roots. In the UK the usual suspects are leatherjackets, the larvae of crane flies, and chafer grubs, the larvae of beetles. The two look different, follow different calendars and call for different timing if a biological treatment is used. This article summarises the Royal Horticultural Society (RHS) profiles for leatherjackets and chafer grubs in lawns, which are written for gardeners across the UK. It does not cover pesticides, which the pages read do not discuss. It is general information.
Telling the two apart
The RHS describes leatherjackets as elongated, tubular, greyish-brown larvae up to 30mm long, with no visible legs or distinct head. Chafer grubs, by contrast, have stout white bodies curved in a C shape, light brown heads and three pairs of legs at the head end, reaching up to 18mm when straightened. The RHS says the species that most often damage lawns are the garden chafer and the Welsh chafer, and that lawn chafers live in turf, unlike similar-looking grubs such as stag beetle larvae, which are associated with dead wood. Identification matters because a treatment timed for one grub will miss the other.
Life cycles and when damage shows
Leatherjackets
Adult crane flies emerge between August and October and lay eggs in turf. The eggs hatch weeks later and the larvae feed on roots through the winter. The RHS notes that mild winters allow faster growth, while cold winters can delay significant damage until mid-summer.
Chafer grubs
Adult beetles emerge from late May through June and lay eggs in turf. The larvae feed on roots through autumn and winter without initially causing much damage, and pupate in the soil in spring. The RHS says damage is most noticeable between autumn and spring, and that infestations tend to be localised and sporadic.
Signs to look for
- Yellowish-brown patches where roots have been eaten.
- Small round holes made by birds such as crows, magpies and starlings probing for leatherjackets, according to the RHS.
- For chafer grubs, turf torn up by crows, jays, magpies and rooks, and by badgers and foxes, which the RHS says do this to reach the grubs. In this case the animals cause most of the visible destruction.
- Seedlings collapsing when leatherjackets eat stems at soil level.
- Larvae in the surface layers of soil when a patch is lifted, which is direct confirmation.
Where badgers are responsible, legal protection limits what can be done. The site’s article on badgers damaging a garden or property explains the position in England, Wales and Scotland, and the piece on urban foxes covers the other digger.
Biological control and its timing
The RHS describes nematode treatments for both grubs, though the products differ. For leatherjackets, the RHS says pathogenic nematodes of the species Steinernema feltiae or S. carpocapsae are watered into turf or soil and infect the larvae with a bacterial disease. They need well-drained but moist soil and a minimum temperature of 12°C, and the RHS advises applying them preventively from September to early October. For chafer grubs, it describes nematodes of the species Heterorhabditis bacteriophora, applied when soil temperature is between 12°C and 20°C and kept moist, with July to September offering preventive benefit before damage becomes visible.
The timing point is crucial. The RHS’s general page on biological control explains that nematodes are living organisms, usually supplied by mail order, mixed with water and watered on, and should be used as soon as possible after they are received. It adds that they should be used with care, and only when there is a specific problem to treat, because they can infect non-target animals within the insect or mollusc groups. By the time lawn damage is obvious, cold soil may make treatment ineffective, which is why the advice centres on prevention in late summer and early autumn.
Repair and habits
For chafer damage, the RHS advises repairing lawn areas in mid to late spring, when the grubs have moved deeper into the soil to pupate, by re-seeding or re-turfing. It notes that lures and traps exist for adult chafer beetles but that their effectiveness is uncertain. It also points out that most crane fly species are beneficial, helping recycle nutrients, and that birds rely on leatherjackets as food.
Using a lawn-care company
Lawn treatment firms may offer grub control. A sensible customer asks which grub is present and how it was identified, which product and species of nematode will be used, when soil temperature suits it, and whether a return visit is included. Written scope and follow-up, as discussed in the site’s guide on costs, callouts and quote comparison, help avoid paying for a visit at the wrong time of year.
Common questions
Is a bird-damaged lawn always a grub problem?
Not necessarily, but the RHS lists bird probing and torn turf as classic signs, and finding grubs in the soil confirms it.
Is autumn or summer the right time for nematodes?
According to the RHS, September to early October for leatherjackets, and July to September for chafer grubs.
Does this apply outside England?
The RHS pages are UK gardening advice and are not limited to one nation, though wildlife protection rules for badgers differ and are covered separately.
The bottom line
Leatherjackets and chafer grubs both eat lawn roots, but they differ in appearance, calendar and nematode species. The RHS focuses on identification first, preventive nematode timing in late summer and early autumn, spring repairs for chafer damage and a tolerant view of wildlife feeding on the grubs. Any paid service should be able to explain which grub it is treating and why the timing suits it.
Sources
- Royal Horticultural Society, “Leatherjackets” (rhs.org.uk)
- Royal Horticultural Society, “Chafer grubs in lawns” (rhs.org.uk)
- Royal Horticultural Society, “Biological control in the garden” (rhs.org.uk)