Gardens for Biodiversity: Insects
Cecilija Rubenis, 30th Jan 2025
A Christmas Beetle amongst Ficinia nodosa and Banksia robur.
One of the great pleasures of creating a garden is watching it take on a life of its own, humming with insects. The sheer number and diversity is astounding - from the noisy Blue Banded Bees visiting the cup-shaped flowers of Bulbine bulbosa to the tiny, iridescent Cuckoo Wasps searching for a safe place to nest, it’s a joy to pause and observe as they go about their day. Aside from the beauty and interest they bring to our gardens and landscapes, insects play many critical ecosystem functions, such as pollination, decomposing and nutrient cycling, controlling pest species, and fulfilling an important link in the food-chain. As the CSIRO puts it, “The planet would cease to support life without the services insects provide.”
Plants in the Asteraceae family, such as this Xerochrysum viscosum, are a magnet for a range of insect species.
The problem
It’s no secret that insect populations worldwide are in decline, which in turn has huge impacts on the larger birds, mammals, and reptiles that feed from them. For example, the well-documented drop in Bogong Moth numbers in alpine and subalpine regions of NSW and Victoria is proving devastating for the endangered Mountain Pygmy Possum, with fewer than 2000 of these marsupials left in the wild. Globally, research published in 2019 suggests that on average 41% of known insect populations are in decline. In Australia, entomologists believe that most of our insects have yet to be identified and comparatively little is known of this vast and complex area of study. Anecdotally it is often remarked that Christmas Beetles are not as common as they used to be. As a child I have vivid memories of summer nights spent camping, picking huge beetles from my hair and clothes in-between rounds of Uno. Driving home at night in rural NSW meant arriving with a windscreen covered in sticky bug-squish. This is now very rarely the case.
So what’s causing the issue? It’s the usual suspects - according to the University of Sydney’s Dr Francisco Sanchez-Bayo, the major factors include habitat loss, the use of pesticides and fertilisers (as well as other forms of pollution), biological threats such as pathogens and introduced species, and climate change.
The issue is mammoth in scale and it would be tempting to bury our heads in the sand; however, the good news is that as gardeners and earth-lovers, we have real power to protect and nurture our local insect populations.
A dragonfly resting on a warm rock in my pond. There are 325 species of dragonfly and damselfly in Australia.
How to help
Change your habits and ditch insecticides
Former Director of Horticulture at New York’s Brooklyn Bridge Park, Rebecca McMackin, notes in her TED talk, “an incredible amount of damage has been done in the name of making pretty gardens…there just isn’t a garden pretty enough to be worth all of that.” She continues, pointing out that “Gardens can, and have, brought back plants and animals from the brink of extinction.”
There are many accepted gardening practices that are immeasurably harmful to our insects and the life they support (which is to say, all of us).
The maintenance of a pristine lawn will call for a huge use of resources such as water and fertiliser, as well as the use of insecticides known to be harmful to insects and their larvae. An example of this are products that promise to control ‘curl grub’, a generic term applied to beetle larvae that feed on grass roots and organic matter, leading to brown patches in lawns during the warmer months. Many of the curl grubs found in lawns are Sarab Beetles native to Australia, including our iconic Christmas Beetle. These beetles have suffered from loss of habitat as they favour open grassy woodlands, many of which have been cleared for housing development or agriculture. With this in mind, it’s no wonder they’re trying to make a home in our backyards. If you do have lawn, water in the morning rather than the evening - soggy lawn left overnight is more likely to lead to large numbers of curl grubs.
Be wary of all fly sprays and garden insecticides, even those that are labelled ‘organic’ or ‘natural’ - even naturally-derived and homemade products are harmful to insect life, indiscriminately killing pest species as well as beneficial insects in your garden. By using these products you’ll be shooting yourself in the foot, harming insects that will help to control pests. Commonly seen beneficial insects include Hoverflies and Lady Beetles, both of which control aphids. Paper Wasps are also a gardener’s friend, controlling Cabbage White Butterflies that love to eat our brassicas, such as broccoli and kale. Although wasps can have a nasty sting, in general if you leave our native wasps alone they will leave you alone. We have three wasp nests (that I know of) in our small back garden, but I’m more than happy to have them sharing our space and helping to maintain the balance. So far, I haven’t had any issues, and the birds in my garden also have a wasp-feast every now and then, keeping populations at a manageable level.
Although spiders are not insects, on the same principle I choose to mostly leave them alone when they make homes on the outsides of our windowsills. Even though I am a recovering arachnophobe, I know that these predators are part of the amazing and complex ecology in our garden that keeps the system healthy and functioning well. For that, I am very grateful.
This flower spider (perched on Xerochrysum ‘Dargan Hill Monarch’) is a leaf and petal-dweller, relying on camouflage to capture its prey.
Rather than immediately turning to insecticides when we first notice a problem, instead take a moment to pause and observe. For example, the aphids you’re trying to control on your roses may very well be housing the larvae of tiny wasps, which parasitise the aphids and turn them into a metallic bronze ‘mummy’. The wasps hatch in these aphid mummies, continuing the lifecycle and hunting more aphids. The key to discovering these beneficial interactions and keeping your garden in good health is to observe, observe, observe. At home, I do this when hand-watering in the morning with a cup of coffee, and when I come home from work, taking a moment to wind down as I move through my garden.
2. Plant flowers, especially endemic species
It’s a lovely thing that one of the key solutions to a catastrophic problem is to grow more flowers. Insects need flowers for nectar and pollen, and in return they enable the plant’s reproductive cycle by pollinating their flowers, which in turn become fruit. This process of pollination leads to the production of many of the fruits and vegetables that we commonly eat every day. Some insects, such as native Blue Banded Bees, pollinate via ‘buzz pollination’ - this involves the insect vibrating rapidly inside the flower, thereby releasing the pollen. This is how many food plants, such as eggplants and tomatoes, come to fruit. In fact, as I sit in my study typing this paragraph, I can hear Blue Banded Bees in my garden noisily buzz-pollinating my tomatoes. Thanks friends!
It’s understandable that many people enjoy having a lawn, especially if you’re the parent of young children or a boisterous hound. However, traditional lawns are ecological deserts, largely devoid of food and forage for insects. Consider minimising your area of lawn and increasing space for flowering plants. As Rebecca McMakin points out, “Lawn should be area rugs, not wall-to-wall carpet.”
Unfortunately, it’s not a ‘one size fits all’ policy when it comes to planting for native insects. Australian insects have developed alongside our unique plant life over millennia, meaning that many of them are specialists when it comes to their food sources. In contrast, European Honey Bees are generalists, meaning they’re happy to forage whatever’s going to collect their nectar and pollen. The huge number of European Honey Bees puts tremendous pressure on local insects, especially our local bees, as they compete for resources.
The Wahlenbergia in my garden are visited by many local insects, including tiny native bees.
The key to nurturing our local six-legged friends is to plant local species. The word ‘local’ or ‘endemic’ refers to plants that are from the place where you’re gardening, whereas ‘native’ is a broader term that could describe a plant originating anywhere in Australia, from NSW to WA to the NT and back again. Exotic species are plants that originate from outside of Australia. Many native plants are grown far outside their natural range, such as WA’s beloved Kangaroo Paws (Anigozanthos sp.) or Flowering Gum (Corymbia hybrids). This is not to say that it’s wrong to plant Kangaroo Paws if you love them - heck, Cam and I both have them in our gardens - or that you can’t grow exotic plants in your garden. It means that if you can, find a space for some of our wonderful local species; if there’s one thing I know about gardeners, it’s that they are experts at finding room in their gardens for more plants.
The other important factor to consider when planting for insects are host species. Host species refer to plants that house eggs, larvae or pupae, as well as food plants that are necessary to insects when they’re in their larval stage. An example of this are the caterpillars you might notice on your citrus leaves - these caterpillars are the larval stage of either the Dainty Swallowtail or Orchard Swallowtail Butterfly. Remember, without caterpillars, there are no butterflies.
Other host species that support local butterflies in the ACT include grasses such as Poa labillardierei and Microlaena stipoides, Kangaroo Grass (Themeda triandra), Lomandra (such as longifolia and cultivars), Paper Daisies (Xerochrysum viscosum, X. subundulatum, X. bracteatum), Wattles (Acacia sp.), and Native Blackthorn (Bursaria spinosa). Adult butterflies also benefit from having rocks placed in the sun for them to bask on.
Some plants for the Canberra region that nurture insect populations are found in the list below. Local species are marked with an asterisk*.
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Black She-Oak - Allocasuarina littoralis*
Native Blackthorn - Bursaria spinosa* (prickly)
Kurrajong - Brachychiton populneus*
Wolgan Snow Gum - Eucalyptus gregsoniana (an almost-local, endemic to higher altitude areas around Braidwood, the Budawangs, and the Blue Mountains)
Dwarf Snow Gum - Eucalyptus pauciflora ‘Little Snowman’
Little Sally - Eucalyptus moorei
Snow in Summer - Melaleuca linariifolia
Melaleuca linariifolia ‘Seafoam’
Weeping Myoporum - Myoporum floribundum (small flowers are fantastic for tiny insects)
River Bottlebrush - Callistemon sieberi*
Silver Banksia - Banksia marginata*
Coastal Banksia - Banksia integrifolia
Old Man Banksia - Banksia serrata
Swamp Banksia - Banksia robur (keep out of areas prone to heavy frost, can handle extra moisture)
Woolly Tea Tree - Leptospermum lanigerum* and cultivars
Slender Tea Tree - Leptospermum brevities*
Poverty Bush - Kunzea ambigua
Black Wattle - Acacia mearnsii*
Silver Wattle - Acacia dealbata*
Hickory Wattle - Acacia falciformis*
Blackwood - Acacia melanoxylon*
Grevillea arenaria
Grevillea rosmarinifolia* (prickly)
Wax Flower - Philotheca myoporoides and cultivars
Correa species and cultivars
Crowea species and cultivars
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Common Tussock Grass - Poa labillardierei*
Snow Grass - Poa sieberiana*
Weeping Grass - Microlaena stipoides*
Kangaroo Grass - Themeda triandra*
Mat Rush - Lomandra species and cultivars (not our favourite but undoubtedly a useful and important plant - we prefer to use cultivars ‘Katrinus Deluxe’ and ‘Tanika’. Avoid planting too close to walkways due to prickly flowers and foliage).
Chocolate Lily - Dichopogan fimbriatus*
Vanilla Lily - Arthropodium milleflorum*
Billy Buttons (tall)- Pycnosorus globosus
Billy Buttons - Craspedia variabilis*
Purple Loosestrife - Lythrum salicaria* (we plant this in our wetlands so it has constant access to moisture)
Native Bluebell - Wahlenbergia sp.*
Cut-leaf Daisy - Brachyscome species and cultivars* (some less common species are endemic to the ACT - we have mixed success with Brachyscome but currently ‘Pacific Cloud’ is looking nice in my garden)
Rhodanthe anthemoides (alpine form - available from Greening Australia)
Flax Lily - Dianella sp. and cultivars* (some species are endemic)
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Kunzea ‘Badja Carpet’
Yellow Buttons - Chrysocephalum apiculatum*
Alpine Grevillea - Grevillea australis*
Fringed Heath Myrtle - Micromyrtus ciliata* (prostrate form)
Creeping Boobialla - Myoporum parvifolium
Observations from the kitchen garden
Although planting endemic species is the best way to support our specialist insects, there are many non-native plants that our local insects still enjoy. The Blue Banded Bees in my garden visit many local species, but they also love the flowers of salvias such as Salvia ulignosa and culinary Sage, daisies such as Cosmos, and common companion plants such as Borage and Comfrey. Many insects also love umbelliferous flowers such as those found on Parsley, Dill, and Fennel, or flowers like Achillea, Queen Anne’s Lace, and Sedum. If you are able to do so, allow vegetables and herbs to go to flower and seed - the flowers are fantastic for insects, and the seeds may be eaten by birds such as Crimson Rosellas (unless you harvest them for your seed-bank first!)
A Blue Banded Bee in my kitchen garden visiting the bright blue flowers of Salvia ulignosa.
3. Give yourself permission to be messy
Our constant desire for tidiness does biodiversity a great disservice. It harks back to gardens of the past, where exerting control over nature in a garden was used as a status symbol, such as in the grand formal gardens of Italy and France. However, the world is wide and wild, and the reality is that there is very little within our control. If we are able to embrace a different style, one that is texturally softer and more relaxed, not only does it cut out a huge chunk of maintenance (I definitely try to avoid spending time on the end of a hedger, and my back thanks me for it), but it creates habitat and opportunities for biodiversity to thrive. Many insects nest in hollow stems, overwinter in fallen leaves, and burrow into clay. If we are able to leave autumn leaves in place as mulch, and consider leaving dried stems on our perennials for a little longer, we might be surprised to find out who has taken up residence. This softness in garden design has been made famous by designers such as Piet Oudolf, whose layered and textural gardens around the world speak to the beauty of plants throughout their lifecycle, rather than just favouring them for their blossoms in spring and summer.
Another garden embracing this technique is the Walled Garden at Knepp Castle in West Sussex (also home to a larger-scale rewilding project). The gardens, headed up by Charlie Harpur, powerfully and beautifully demonstrate how garden design and gardening practices can break free of past traditions and explore a future that is as beautiful as it is diverse.
Piet Oudolf’s garden, Oudolf Hummelo, in Autumn.
Source: https://oudolf.com/garden/oudolf-hummelo
Oudolf Hummelo in winter. This soft, textural look is able to be achieved using some of our Australian plants.
Source: https://oudolf.com/garden/oudolf-hummelo
4. Build an insect hotel, or two, or three
Another great way to incorporate insect habitat into your garden is by building them their own hotel. This can be as simple as a bundle of sticks tied together and hung in a tree, or as complex and creative as a bricks-and-mortar home.
In the video below, Sophie from Gardening Australia demonstrates different types of ‘bee suites’ to house different species of native bees.
https://www.abc.net.au/gardening/how-to/bee-grade-hotels/13262244
5. Dim the lights
Many of our nocturnal insects, such as the Bogong Moth, become confused in the presence of artificial lighting. Research suggests that the lights from our cities disrupt the Bogong Moth’s ability to navigate, affecting its ability to migrate, feed, and reproduce. This in turn has flow-on affects for their predators, such as the Mountain Pygmy Possum. Minimise and switch off outdoor lights at night when not in use - our local moths will thank you for it.
A tiny pollinator enjoying the cheerful flowers of Pycnosorus globosus.
It can be overwhelming to consider the environmental catastrophes that are occurring worldwide - I sometimes feel completely overcome with worry and grief. The thing that brings me out of that place is gardening with a purpose - it is what helps me make sense of the climate crisis, and brings me hope for the future. For each gardener who spreads the word and leads by example, another may follow. Each biodiversity garden nurtures our insect populations, as well as nurturing our spirits when we can look out the window and see a rambunctious garden full to bursting with bees and butterflies.
Until next time, keep up the gardening, it’s doing a world of good 🦋💚
References and further reading
Let Your Garden Grow Wild | Rebecca McMackin | TED:
https://www.youtube.com/watch?v=qxgE0q1_m6U
Emma Cutting | The Heart Gardening Project and Melbourne Pollinator Corridor:
https://theheartgardeningproject.org.au
Australian Native Plans Society Canberra Region Inc. (2018) Australian Plants for Canberra region gardens and other cool climate areas (5th edition). Canberra: Australian National University Printing Service.
Bond, S. et al. (2018) Field Guide to the Butterflies of the Australian Capital Territory. Canberra: NPA Publication Working Group.
Crawford, D. (2015) Garden Pests, Diseases & Good Bugs. Sydney: HarperCollinsPublishers.
https://www.zoo.org.au/fighting-extinction/local-threatened-species/mountain-pygmy-possum/
https://australian.museum/learn/animals/
Knepp Rewilding Projects:
