Garden Ecosystems Part One: Pest Predator Dynamics and Balance 21   Recently updated !

Start seeing your outdoor space as an ecosystem rather than a garden​

The more I learn about edible gardening, the more I learn the importance of “bugs” in successful gardening. Often, you are too busy concentrating on day to day gardening tasks to see that pest issues come and go in your own garden. You see aphids today, aphids tomorrow and aphids the next day.  You feel there is a problem that is not resolving itself, and you reach for a quick fix.

When I was performing ongoing maintenance for my clients, and visiting their gardens every two weeks, it was a perfect time frame to see the ebbs and flows of pest predator interactions.

Good Bugs and Bad Bugs

The concept of “good bugs” and “bad bugs” is not a new one. However, in this article I’ll try to convince you that there’s no such thing as a bad bug! Instead you need to look at your garden as an ecosystem that contains a species rich diversity. All of the bugs should interact to achieve a “balance”.

Traditional “Bad Bugs”

Most “bad bugs” are labelled so, because they feed on, and damage plants in the garden. They are usually sap sucking insects, or leaf chewing insects. This damage weakens the plant, reduces the potential yield and may even kill the plant. Sap sucking insects can also transfer diseases such as mosaic virus between plants. Some of these bad bugs are:


Earwigs chew holes in leaves. They cause damage especially to fresh young fruit tree leaves in spring. They also have a liking for bean seedlings, lettuces and broad beans. I’ve outlined some traditional earwig control methods in a blog post.

Earwigs are also the great decomposers in the garden and as discussed below this is a silver lining to a perceived problem.

Bad Bugs in the garden

Slugs & Snails

Snail bad bug garden

Slugs lay their eggs in soil and emerge to feast on tender young seedlings. They are often prevalent during and after rain.

Traditional methods of control for slugs and snails are snail pellets and beer traps.

I’ve noticed that using sugar cane mulch attracts slugs and snails into the garden. This is because the sugar cane is full of sugar and yeasts, and these are the very same things that attract the slugs and snails to beer traps. The sugars and yeasts also attract the snails and slugs from the mulch into your patch. See this post for more information on mulch.


Aphids are profusely breeding, sap sucking insects. There are many different species, some of which have specific hosts such as the Allium Aphid (Neotoxoptera formosana) and the Cabbage Aphid (Brevicoryne brassicae). They are tiny and can be green, grey, brown and black in colour.

Aphids quickly breed up via asexual and sexual reproduction. The adult stage of the lifecycle has wings enabling them to fly (often with the assistance of the wind) to infest nearby plants.

Aphids can transport plant viruses between plants and are often accompanied by ants (see below)

Good Bugs vs Bad Bugs Aphid


Whitefly is another sap sucking insect that can be noticed as clouds of white insects lofting from plants as they are disturbed. They cause speckled damage to leaves. Population explosions can be greater in some years than others, depending on the local weather conditions. See some traditional control methods in my blog post.

White Cabbage Butterfly

White cabbage butterfly cause lots of damage to winter brassica crops. It is the small, green caterpillar that causes the damage by chewing holes in the leaves of plants. Small seedlings are most susceptible to damage and entire crops can often be wiped out by this pest. I’ve written an extensive blog post on control methods for white cabbage butterfly.

Autumn planting melbourne white cabbage moth


Citrus pests and diseases in Melbourne

Scale are a sap sucking insect often found on citrus trees and other plants. They are waxy and difficult to control with sprays. I’ve noticed that scale tends to infect weakened trees (eg citrus trees that haven’t been fertilised for a while). They are often accompanied by ants (see below)


Ants aren’t what we would normally call a garden pest or “bad bug”. However, they are often associated with bad bugs such as scale and aphids. This is due to a symbiotic relationship that they share.

good bug bad bug resilient ecosystem

Sap sucking insects such as aphid and scale don’t have actively moving mouth parts. This means they don’t actually “suck” the sap out of the plant. Instead they insert their proboscis into the vein of the plant and use capillary (wicking) action to extract the sap. The sap flows up through the proboscis and some of the sugars from the sap are extracted as they take it up. To enable the capillary action to flow, they excrete the rest of the sap out through their “bottom” as honeydew.

This honey dew is rich in sugar and the ants greedily use it as a food source. In return the ants protect the scale and/or aphids from predation. Ants have also been observed moving the scale and aphids around the plant to encourage their spread. They effectively “farm” the sap suckers.

Ants are a symptom of a pest infestation, but not a cause of damage to the plants themselves.

Part 26 of my Vegetable Patch from Scratch series looks at some of the common pests of the vegetable patch in more detail.

What are some of the Traditional "Good Bugs"?


Lacewings are very generalist predators and control aphids, scale, whitefly, mites, mealybugs and all manner of sap suckers in the garden.

Their larvae, called ‘antlions,’ will eat massive numbers of pest critters over their lifetime. They can be difficult to spot as they use debris such as dust and aphid exoskeleton to cover their back as a disguise.

Gardening Good Bugs and Bad Bugs
Lacewing eggs good bugs ecosystem garden
Lacewing eggs such as these are often found in gardens that are a healthy ecosystem.

You may notice the eggs of the lacewings in and around your garden. I often spot them stuck to dark objects such as black plastic pots. The tiny eggs are held on with thin stalks to stop ants from predating on them.


Good bugs and bad bugs in the garden

Ladybirds are one of the most commonly known “good bugs” in the garden. There are many different varieties that you might find in your garden. Most of them are beneficial and eat anything from aphids and whitefly, through to fungus such as powdery mildew.

The larvae stage look nothing like ladybirds. It is this larval stage in a lot of the species, that is most useful to gardeners

Praying Mantis

Mantises are fantastic generalist predators in the garden. They’ll eat any other arthropod that they can reach. They are ambush predators, remaining stationary until prey comes within their reach, and then they strike their prey

Paraying mantis good bug garden


Good Bug Hover FLy in the Garden

Hoverflies are often mistaken for bees or wasps due to their striped yellow and black abdomen. You’ll often find them buzzing around your garden in spring and summer.

The hoverfly larvae is a tiny, blind maggot. They move along plant surfaces looking for aphids to prey on. Once detected, they seize the aphid and digest its juices. The exoskeleton is then discarded.  A hoverfly can eat up to 30 aphids per day.


Spiders are generalist predators in the garden and help control the balance of a large variety of arthropods.

Generalist Predator Good Bugs

Predatory Wasps

good bug garden ecosystem

There are all manner of predatory or parasitic wasps available to help out Melbourne based gardeners. Most of them lay the eggs under the skin of the target species. The eggs hatch inside the host species and the pupae slowly consume the host from the inside out.

Predatory wasps target many different “bad bugs” including aphids, caterpillars, scale, whitefly and even other wasps.

Population Dynamics

I want you to imagine for a minute that you’ve got a huge glass box.

In that glass box are unlimited lettuces.

Now we are going to introduce two rabbits to that glass box. In the absence of predators and with unlimited food, they will quickly breed up at an exponential rate.

If we chart what happens to those rabbits over time it looks something like this.

Good Bugs Bad Bugs Population Dynamics
Initially the rabbit population grows at an exponential rate

After some time, we could introduce two foxes to the glass box. They start eating the rabbits and also start breeding up in numbers.

The rabbit growth rate slows as they get eaten.

Good Bugs Bad Bugs Population Dynamics
Once foxes (predators) are introduced to the system, the growth rate of the rabbits is slowed

The more the foxes breed up, the more rabbits they eat. This causes the rabbit population to dwindle.

After a while, there are not enough rabbits to support the number of foxes that are in the box. So the fox population starts to crash.

Good Bugs Bad Bugs Population Dynamics
Eventually the foxes start consuming more rabbits than are being produced. This creates a reduced net rabbit population and reduced food for foxes. The fox population dwindles.

Correspondingly, with fewer foxes in the box, the rabbit numbers start to increase. This fluctuation keeps repeating in a balanced cycle.

Good Bugs Bad Bugs Population Dynamics
A balanced ecosystem results in small population fluctuations.

Now if we happen to get rid of all the rabbits in the box, what happens to the foxes? Foxes have no food so they can’t exist. So our fox and rabbit population gets out of balance. The foxes cannot live without the rabbits.

Let’s change our thinking from foxes eating rabbits to ladybugs eating aphids. Here you can also see that the ladybugs and other good bugs cannot exist without the bad bugs.

So does that make the Bad Bugs suddenly “Good Bugs”?

The “Good Bugs” can’t exist without the “Bad Bugs”. So, in small balanced quantities I believe that all bugs are good. The key is to make sure that you have a diverse ecosystem and it will be resilient and low maintenance.

Unleashing pesticides in the garden is a terrible idea. Pesticides kill the beneficial insects as well as the targeted “bad bugs”. This means that the population of all the bugs in your garden will crash and you can’t obtain a balanced population dynamic. Once you start spraying, you will need to keep spraying at regular intervals to keep all bug populations low.

The best thing is to just step back and “Do Nothing”. Let nature take care of the “problem” for you!

Look for the good in the “bad”: They all have a silver lining (probably)

Most of the “bad bugs” have good sides to them, you just need to change your perspective to see the silver lining.

For example, earwigs tend to eat a lot of vegetable seedlings. However, they are also nature’s great decomposers. They help break down our composts, and they help break down leaf litter. They also eat codling moth eggs.

European Wasp Melbourne

This is a photo I took a few years ago. It shows a European Wasp attacking a white cabbage butterfly caterpillar. I watched them for ages, slowly dissecting the caterpillar and flying it back in pieces to its nest. So the European wasp is actually helping to control another pest in my garden.

I have huge rat problems in our suburban garden. The rats eat my tomatoes, pepinos, peaches, apples, pumpkins, sweetcorn and cucumbers. It is very frustrating. However, I’ve also noticed lots of little piles of empty snail shells tucked up behind plant pots and other locations. I believe that the rats have been eating the snails and controlling that issue for me. Without the rats, we would possibly be overrun with snails in our garden. More on strategies for dealing with rats here.

Natural control method for snails
With a change in perspective our "rat problem" becomes our "snail solution"!

There are so many similar examples of silver linings with your pest problems. Remember everything in life is a consumer until it gets consumed…. It’s all about balance and supporting the higher level predators.

Just Relax and “Do Nothing” Pest Control!