Don’t kill the grubs in your garden – they may be native beetles

Have you ever been in your garden and found a gigantic, white, C-shaped larva with a distinctive brown head and six legs clustered near the head?

If so, you have had contact with the larva of the scarab beetle (family: Cranesbills) also known as “curly hair”.

Many gardeners fear that these gigantic larvae can damage plants.

So what are grubs? And should you worry if you discover them in your garden?

What are curl larvae?

The grubs turn into scarabs.

There are more than 30,000 species of scarab beetles in the world. Australia is home to at least 2,300 of them, including the rainbow Christmas beetle (Anoplognatus), spectacularly horned rhinoceros beetles (Dynastinae) and beautifully patterned flower beetles (Cetoniinae).

Although adults are the most evident stage of life, scarabs spend most of their lives as larvae, living underground or in rotting wood.

Scarab larvae can assist the environment

Scarab larvae living in the soil can aerate the soil and assist distract seeds.

Species that feed on decaying matter assist recycle nutrients and keep soil hearty.

Most scarab larvae are gigantic and full of protein and fat. They are a perfect meal for hungry birds.

In addition to being significant to ecosystems, scarabs also play a role in cultural celebrations.

For example, the old Egyptians worshiped the sun using a symbol of a dung beetle rolling a ball.

In Australia, colourful Christmas beetles traditionally herald the arrival of the holidays.

Unfortunately, the number of Christmas beetles has decreased significantly rejected over the last few decades, probably due to habitat loss.

Are the grubs in my garden harming my plants?

Most scarab larvae feed on grass roots. In the case of gigantic numbers of plants, this can cause damage.

In Australia Argentine lawn scarab and African Black Beetle are invasive pest species that cause significant damage to pastures and lawns.

Native species of scarab beetles can also become pests under the right conditions.

For example, when Europeans began planting sugar cane (a type of grass) and converting native grasslands into pastures, many native Australian scarab species found a recent, ample food source and were classified as pests.

Unfortunately, we know little about the feeding habits of many native scarab larvae, including those found in gardens.

Some common garden species, such as the beautifully patterned fiddler beetle (Eupoecila australasiae), feed on rotting wood and are unlikely to harm garden plants.

Even root-eating species do not pose a problem under normal conditions.

Plants are surprising resistantand most can handle losing a petite amount of roots to the beetle larvae. Even while damaging plants, the grubs can assist keep the soil hearty by providing aeration and mixing nutrients.

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How can I tell if I have “good” or “bad” beetle larvae in my garden?

Unfortunately, identifying scarab larvae species is complex. Many of the features we exploit to distinguish groups are complex to see without magnification. Although there are identification guides for scarab larvae that can be found in pasturesThere are currently no sources enabling the identification of scarabs found in home gardens.

Since identification may not be possible, the best indicator of whether scarab larvae are a problem in your garden is the health of the plants. Plants with damaged roots may wilt or turn yellow.

Since most root-feeding scarab beetles prefer grass roots, lawn grasses are most at risk, and the damage is usually caused by exotic scarab species.

What should I do if I find grubs in my garden?

The sight of suspiciously plump grubs among the roots of prized garden plants can be disturbing, but you shouldn’t immediately reach for insecticides.

Chemicals used to control scarab beetles harm all scarab larvae, whether they are pests or not.

Many of the most popular grub control products contain chemicals called “anthranilic diamides” which are also toxic for butterflies, moths and aquatic invertebrates.

By disrupting soil ecosystems, insecticide exploit can do more harm than good, and can even kill harmless native beetle larvae.

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So what to do instead?

Larvae found in decaying wood or litter feed on the wood and are useful composters; they do not harm plants and should be left where they are.

Larvae found in composters assist decompose waste, so they should not be left alone.

If you find larvae in your garden soil, exploit the condition of your plant as a guide. If your plants appear hearty, consider simply leaving the grubs where they are. Scarab larvae are part of the soil ecosystem and are unlikely to cause damage unless present in gigantic numbers.

If your plants appear yellow or wilted and you have ruled out other causes, such as under-watering or nutrient deficiencies, consider feeding the larvae to birds or crushing them. It’s not pleasant, but it’s better than insecticides.

Lawns are particularly susceptible to attacks by alien scarab larvae. Consider replacing lawns family soil covers. This increases biodiversity and reduces the risk of damage from alien scarab larvae.

Scarab beetles are attractive and fascinating insects that assist keep soil hearty and provide food for wildlife.