Chafer grubs in garden borders

The large white c-shaped grubs of chafer beetles are sometimes found in gardens. Most do not cause problems, some feed on decomposing vegetable matter and help nutrient cycling. A few species can damage roots including some that feed on turf (see chafer grubs in lawns).

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Rose chafer beetle on hogweed flower
Rose chafer beetle on hogweed flower

Quick facts

Common name Chafer grubs (various species)
Plants affected Many do not damage plants
Main symptoms Large white c shaped grubs with three pairs of legs and a brown head
Caused by Larvae of a chafer beetles
Timing All year

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What are chafer grubs?

Chafer grubs are the larvae of chafer beetles that belong to the beetle family Scarabaeidae, which consists of dung beetles and chafers. There are over 80 species in Britain. Many species are rare or of local occurrence. A majority are dung feeders and are vital in the recycling and disposal of dung. Around 17 species are chafer beetles some feed on decomposing organic matter, others on plant roots. Only a handful of species can cause damage in gardens, even here they can be a valuable part of garden biodiversity. Find out more about the Scarab beetles found in Britain from UK beetle recording.

All scarab beetles have c-shaped larvae that have a brown head and three pairs of legs, a form known as scarabiform. Some closely related beetle families (collectively known as Scarboidea) also have this form of larvae, including the rare stag beetle (Lucanus cervus, family Lucanidae, read more from Peoples Trust for Endangered Species), and the dor (also dung feeders dung) beetles (Family Geotrupidae). If the larvae were associated with buried dead wood (e.g. a tree stump) they are likely to be stag beetle grubs. Other endangered chafer species include the beautiful  metallic green nobel chafer which inhabits decaying old trees. These can be mistaken for rose chafer but have wrinked winged cases as opposed to smooth.

The largest chafer beetle in Britain is the cockchafer or Maybug (Melolontha melolontha) and can reach 50mm in length. Adult maybugs are over 3cm in length and are often attracted to light. They are active during May. more information on this insect is available from the Wildlife Trusts. 

A species of chafer grub is often found in compost heaps, areas rich in rotting vegetable matter and occasionally organic matter rich potting composts. This is the rose chafer (Cetonia aurata). The adult beetles are about 2 cm long and metallic green. The adults can feed on flowers and leaves, this insect is beneficial as it helps the composting process as a grub.

A few species of chafer can occasionally be a problem in garden borders, feeding on plant roots; these include the cockchafer and summer chafers (Amphimallon solstitiale). These have larvae that can feed in the soil for up to three years and occasionally damage the roots of plants.

Garden problems are caused by the smaller garden and Welsh chafers (Phyllopertha horticola and Hoplia philanthus) (up to 20mm) whose grubs are mainly found under turf where they can consume the root system. Animals such as foxes badgers and corvid birds often dig for these grubs in affected turf.
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Cockchafer (adult)
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Rose chafer grubs
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Cockchafer (Maybug) grub
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Cockchafer (adult)
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Rose chafer grubs
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Cockchafer (Maybug) grub
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Symptoms

Chafer grubs found in compost heaps and organic rich soil are often Rose Chafer larvae which do not normally damage plants and are part of the composting process.

Where problem chafer species are present plants lack vigour and examination of plant roots will often show signs of being eaten. Large c-shaped grubs can also be found.

Damage to lawns can be more extensive, for more information see chafer grubs in lawns.

Management

Most species of chafer grub do not need management, they are part of the biodiversity that gardens support. Species such as the rose chafer are beneficial. Other than in lawns, chafer grubs rarely cause damage to garden plants. 

Tolerate the presence of chafer grubs in garden borders, in some cases they are beneficial and they are easily confused with stag beetle larvae, which feed on dead tree roots.

Remove larvae of problem species from soil as they are found. Cultivation of the ground can briefly expose the grubs to predators, such as birds, and make the ground less attractive as egg-laying areas.

Biological control

You can buy pathogenic nematodes, usually Heterorhabditis bacteriophora, which enter the larvae and infect them with a fatal bacterial disease. The biological control is not specific to chafer grubs and other insects may be affected. These microscopic animals can be watered into the lawn or garden border when the ground is moist and soil temperature range between 12-20ºC. This biological control is available from some biological control suppliers and some garden centres. The ground around the edge of affected areas should be targeted to deal with larvae spreading out from  “hot spots”. The nematodes should be applied as soon as possible after purchase, following the suppliers’ instructions. It may be necessary to water the soil before and after application to ensure the soil is sufficiently moist for nematode activity and survival.

Lures and traps are available for adult beetles however their effectivness is uncertain. Adults may be trapped after the damage has already occured. 
 

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Biological control suppliers (pdf document)

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