Garden friend or foe? Putting common 'pests' to the test

The United Nations' International Day for Biological Diversity (22 May) is an opportunity to highlight the importance of supporting our unique biodiversity.

Biodiversity is the complex web that supports life as we know it, including all the plants, animals, fungi and microorganisms we share the planet with, and the (often interconnected) roles they play in our ecosystems.

That’s a big concept, so we thought we’d zoom right into your backyard, an ecosystem of its own with a mix of creatures – big, small, slimy or scaley – with unique functions.

There are a few critters we think we should be trying to remove from our backyards, but are these maligned creatures pests? Or do they help your garden? Let’s find out.

Caterpillars

Caterpillars in your garden can be a frustrating experience, especially when they’re chowing down on your favourite plants.

But before you whip out the pesticide, consider the important role they play in the food web.

Caterpillars are an important food source for birds and wasps, so encouraging these creatures into your garden can keep things in balance.

Even better still, caterpillars that complete their life cycles turn into butterflies and moths, important pollinators we love to have in our garden.

Many people try to attract butterflies with plants like the butterfly bush, but have you considered including plants that cater to their larvae?   

Caterpillars can be fussy eaters, with some species only eating one plant! However, overall, their main foods include sedges, native grasses and mistletoes (but the specific plants depend on the caterpillar).

You can find the best caterpillar food plants for your area on the Butterfly Conservation South Australia website.

So, while it is potentially frustrating to share your garden with caterpillars, wherever possible, try to give them space to grow and turn into beautiful pollinators.

And if you’re really struggling, try vegetable meshing to protect your important plants and veggies.

Verdict: garden friend! 

Spiders

You may find them creepy, but spiders can be a great asset to your garden.

They act as natural insect control, feeding on tasty bugs and keeping those populations in check for you.

This reduces your need to resort to pesticides, which helps all the other critters you want in your garden.

You don’t have to worry about too many spiders if your garden is also home to birds, reptiles, frogs or even other insects. Spiders are food source for all these animals and will keep populations in check.

It’s important to note that while many spiders are harmless, some – like the redback and funnel web spider - can be dangerous to us humans if bitten.

The best way to keep yourself safe is to keep your distance wherever possible, wear protective gloves when gardening, and try to keep them out of your house (or relocate them if they find their way inside).

For more information on spider bites, visit SA Health’s website.

You can also find more tips to peacefully co-exist with spiders in our blog.

Verdict: garden friend! 

Wasps 

You may be familiar with European wasps, an introduced species now found widely across the state and much of the country.

They are known to be highly aggressive if disturbed, so it is a good idea to try and avoid these pests moving into your garden. You can do this by clearing up fallen fruit and uneaten pet food, and making sure you keep compost and rubbish bins covered.

If you find a European wasp nest on your property, contact a licensed pest controller.

But don’t let this aggressor give all wasps a bad name – there are many native species that play an important role in your garden. 

Australia has many species of native paper wasps which can be found across much of the country. These insects play a role in the food web by feeding other species - like the caterpillars we mentioned earlier – to their larvae. 

The spider wasp is another friend, helping to control spider populations.

While these species have important roles to play in your garden, they can still deliver a sting if disturbed, so we still recommend giving them space.

Verdict: Garden friends and foes – keep your eyes peeled for invasive species 

Flying foxes 

They may seem scary, but these nectar-loving bats can be great assets for your garden. As pollinators, they disperse native seeds and pollen while foraging for food. 

Grey-headed flying foxes haven’t always been found in large numbers in SA, but they’re protected by our National Parks and Wildlife Act 1972 and considered native.

In recent years, flying foxes have been found in more areas across South Australia – beyond the well-known colony in Adelaide’s Botanic Park – likely because of habitat loss, competition for food resources and the effects of climate change across the eastern states.

They sometimes travel more than 20 km in a night while searching for food, so you may see these nocturnal creatures in your garden. They might be looking for something to eat or sleeping before making the trek back to camp.

If you’re worried about sharing your home-grown fruit, you can use wildlife friendly netting to keep flying foxes and your harvest safe.

You can also consider:

• Keeping fruit or habitat trees pruned.
• Bagging hanging fruit with brown paper or hessian bags.
• Removing unwanted fruit from trees early (e.g. from palm trees).
• Placing reflective or shiny deterrents (like CDs or aluminium strips) in tree branches.
• Bringing washing inside overnight.

Like most bats, grey-headed flying foxes are harmless in themselves, but they can carry viruses that can be deadly to humans. While the risk is small, only people vaccinated against rabies should handle bats.

If you find a sick, injured or dead flying fox, do not touch it, and contact a native animal rescue organisation like Bat Rescue SA (0475 132 093) for assistance. You can also search the internet for other wildlife rescue groups near you.

Be sure to visit SA Health’s website for more information on disease risks and how to stay safe around bats.

Verdict: Garden friend! 

Rats and mice 

None of us appreciate sharing our gardens with feral brown or black rats, which can flock to the warmth and ample food in our veggie gardens.

Gardening Australia has some tips on rodent-proofing, but it’s also important to stop and consider whether you’re really contending with invasive rats and mice at all.   

The native yellow-footed antechinus is actually a marsupial but is commonly mistaken for the common house mouse.

This vulnerable species can control your insect populations – its favourite cuisine - and sometimes spiders, cockroaches, lizards, small birds and even mice.

If you live on Fleurieu Peninsula or in the Adelaide Hills region, the yellow-footed antechinus is one to keep your eye out for.

Also found within coastal and marshy areas of Fleurieu Peninsula – as well as Kangaroo Island and the South East – is the rare native swamp rat.

Swamp rats are herbivores and have been known to move into veggie gardens, and if they are doing damage you can find tips on deterring them in our blog.

A key sign you’re sharing your garden with a swamp rat is a network of ‘tunnels’ or ‘runways’ through thick, long grass and vegetation, which they use to get from burrow to burrow. Fun fact: this aids with soil turnover and health.

It’s important to be aware of the different kinds of animals we share our state with as native wildlife is protected under the National Parks and Wildlife Act 1972 – meaning you can’t employ the same trapping/baiting approach you may use for feral rats and mice.

Verdict: Garden friends and foes – keep your eyes peeled for invasive species 

Possums 

While SA has more possum species than you might think, you’re most likely to encounter the common brushtail or common ringtail possum in your backyard.

Urban expansion has reduced their preferred natural woodland habitats and gum tree hollows available, meaning possums have had to adapt to find shelter and food alongside us instead.

While potentially frustrating to have a possum move into your backyard and chomp down on your fruit trees, it may be the safest habitat they can find.

They also play a role in pollination by dispersing and transferring pollen and seeds. As omnivores, brushtail possums may also help control insect populations.

As a native and protected species, we know we need to try and live with possums. But since they enjoy a wide variety of fruits, vegetables and plants, it is possible for them to do some damage.

Top tips to peacefully co-exist with these furry marsupials include:

• Trim back branches that are overhanging roofs, fences or walkways.
• Provide wildlife nest boxes in your garden as an alternative home. 
• Restrict access to your key fruit trees, vegetable or grain crops using ‘tree collars’, fence barriers or wildlife friendly netting.
• Plant alternative food sources instead, which could include natives like banksias and hakea.
• Consider incorporating plants that possums don’t find as tasty – like native mints and creeping boobialla.
• Remove overnight access to pet food.
• Keep pets inside a night.
• Guard gutters and pipes to exclude droppings.

You may find a possum moves into your roof instead of your garden, but don’t worry, we have advice to deal with that issue as well.

Check out this video from our friends at Green Adelaide for even more great tips:

Verdict: Garden friend!

Understanding biodiversity

Biodiversity is the foundation that keeps our natural world functioning, and it starts closer to home than many of us realise.

Your garden, no matter how small, is part of a living food web where plants, insects, birds, mammals and microorganisms are all connected.

From bees and butterflies pollinating flowers to spiders and wasps keeping insect numbers in check, each species plays a role. Even the creatures we may not love as much have a job to do!

By creating spaces with diverse plants and encouraging a wide variety of creatures into your garden – you can help strengthen our natural systems, build resilience and allow nature to do what it does best: regulate itself.

In doing so, our gardens become healthier, more resilient, and alive with the small, everyday interactions that sustain life well beyond the garden fence.

Some final tips to support biodiversity in your garden include:  

• Plant natives
• Mix up your plant selection to encourage a healthy environment and provide different forms of habitat – think groundcovers, grasses, shrubs of different shapes and sizes and trees (where space permits)
• Consider nest boxes to replace lost habitat
• Reduce your use of herbicides and pesticides

Want more tips like these? Check out 10 ways you can improve biodiversity or how to make a frog pond in your garden.