Last week, we began a two-part series on garden pest predators with Jessica Walliser and discussed the predator/prey cycle taking place in all our landscapes as well as the cues that signal to good bugs that a meal is available. If you haven’t checked out that episode, I recommend you begin there before diving in this discussion on top predatory beneficial insects.
In this episode, we cover some of those specific predators we want in the garden as well as steps to draw in and protect them. Although Jessica isn’t an entomologist by trade, she has discovered that her passion for the world of bugs has even surpassed her interest in her horticultural training and background.
Jessica has written a book on the subject of beneficial insects, and it draws from thousands of hours she spent in observation as well as extensive research. She is a strong proponent of taking a wait-and-see approach to garden pest management – allowing those natural predator/prey cycles to play out and bring the harmonious balance which comes from the voracious activity you might not realize is happening.
Top Five Garden Predators
As a culture, we’ve been trained to loath or even fear bugs. When we find them in the garden, our first instinct is often to remove or destroy them immediately. But this is the wrong approach.
Did you know that only 1% of all insects are considered pests? Nearly all of the thousands and thousands of insect species are considered beneficial (or at least neutral) bugs. With so many insects from which to choose, a top five list can’t effectively be narrowed down to specific species. Instead it’s best to think in terms of categories. Within each category are hundreds or even thousands of species which provide their own unique skills and preferences to seek out and destroy pests.
There are over 1,300 species of tachanid flies in North America. Although you may never have heard of them, they are all around you in the garden. When you see a fly sipping nectar from your flowers, you aren’t looking at a house fly. You are looking at a powerful good bug. Adult tachanid flies look like house flies, but they are actually pollinators.
As a pollinator, they are a benefit to our plants and crops, but it’s their larval stage which should really get you excited. The larvae are parasitoids – they tunnel into garden pests and eat the pests alive.
Many species of tachanid fly will feed on just one species or category of prey, such as aphids. The female tachanid locates that specific type of pest through various cues sent out by plants or the pests themselves, and she lays her eggs on the back of those insects. Once the egg hatches as larvae, it burrows its way into the pest and devours its way out. The end result is always the death of the pest.
Some tachanid fly species lay their eggs in the path of the pest. The insect consumes the fly egg while consuming your plant – not a good meal choice, since the tachanid fly egg will hatch as larvae and eat its way out of the pest. Goodbye pest.
So how do you get more tachanid flies into your garden to enjoy this pest feast? Add asters and dill to your beds. These are two popular food sources for the pollinating adult tachanid fly. As the flies are drawn in to feed on the nectar of these plants, they will also be seeking out prey in the area as a future food source for their young.
Hover or Syrphid Flies
Yes – more flies, and there are hundreds of species which fall into the group of the hover or syrphid fly. These insects often have yellow stripes, so they are easily mistaken for bees. Like bees, adult hover flies move from flower to flower and provide important pollination as they feed on nectar.
How can you know which is which? Bees have two pairs of wings, while flies have just one pair. When you think you are watching a bee at work, take a closer look. If it has just one pair of wings, celebrate – you’ve found yourself a hover fly.
While she is at work pollinating, the female hover fly is also seeking out prey for her offspring. Once she finds them, she lays her eggs around the pest colony. The hatched larvae crawl around on the plant to locate the pests and consume them.
Here’s where it really gets interesting: The female hover fly is able to sense the size of the pest colony and adjust the quantity of eggs she lays in correlation with the prey population. Large colony – lots of eggs. If the pest colony is small, she lays only a few eggs. Any eggs she doesn’t lay are reabsorbed by her body to be used as energy as she goes about her pollinating business. Nature is a remarkable wonder.
Minute Pirate Bug
Speaking of remarkable, the minute (my-noot) pirate bug is the third in Jessica’s list of top garden predators. There are only a handful of species of this tiny insect in North America, but they are very common in most gardens.
How can you spot a minute pirate bug? You’ll need a little patience and a keen eye. Their wing covers don’t extend to the end of the bugs’ 1/16” long bodies, so you will see a silvery diamond shape on their back end.
These insects have a needle-like mouthpart called a rostrum. They use this rostrum to pierce the soft bodies and suck out the innards of pests like whiteflies, aphids, scale, and rose thrips. Picture, if you will, a garden pest milkshake. Delicious.
Minute pirate bugs prefer to feed on pests, but in early spring – when there isn’t enough prey available as a food source – minute pirate bugs will eat nectar and work as pollinators. Since they are small and feed through that tiny mouthpart, minute pirate bugs prefer plants with tiny flowers. By incorporating plants like crimson clover, oregano, wild mustard, etc. (look for plants with a shallow nectary), you will be feeding these buccaneer predators early in the year, so they will be able to stick around and turn their appetites toward your bad bugs.
Who likes wasps? Well, we all should. There are over 6,000 species of parasitic wasps in our North American gardens. You might say insects have an hourglass figure. If you spot a wasp with a pinch waist, odds are good that you’re observing a type of parasitic wasp – especially if that wasp is eating nectar.
Although they are commonly referred to as “parasitic wasps,” they are actually parasitoidal. They will kill their pest prey. They tend to be specific in their prey of choice, but an often-preferred meal is the tobacco or tomato hornworm. Many species of parasitic wasp use hornworms to house and feed their young. The Cotesia wasp, for example, will lay between 1 and 300 eggs just under the skin of one hornworm.
The hornworm is a massive food source, so the Cotesia wasp egg larvae take their time. They feed on the non-essential tissue of the hornworm before they really move in for the kill by feeding on the essential parts.
By the time we spot what looks like grains of white rice clinging to the body of the hornworm, death is close at hand. At this stage, the larvae will have devoured enough of the hornworm that it has just about two weeks to live. Meanwhile inside the tiny white cocoons which look like rice, the larvae develop into adults. Within 10-14 days, the now-adult wasps will cut their way out of the cocoon and fly off to begin this cycle all over again on more pest victims.
If you know much about hornworms, you know that they can do significant damage in a short period of time, so you might not like the idea of keeping them around as a living incubator during this slow death. Yet, it is the hornworm’s feeding habits which are your best clue as to what’s really going on.
Hornworms feed and are easier to locate at night. So if you have hornworms in your garden, spend a little time inspecting your plants under the stars. These insects stop feeding almost immediately after they have been parasitized by a wasp. So when you spot a hornworm which isn’t actively feeding during this nighttime check, leave that hornworm alone. A hornworm that isn’t eating at night is a hornworm being eaten alive by predators.
In other words, wasp eggs and larvae are already at work for you before you can ever see them. By the time you spot cocoons, the lifecycle is nearly complete. When you understand this process and allow the living meal to remain on your plant, you are ensuring a new generation of good bugs will have the opportunity to mature and continue protecting your future plants.
If you’d like to make your nighttime hornworm hunt a little easier and more colorful, try a UV flashlight (commonly available online). Many varieties of caterpillar will glow under UV light, and the hornworm is no exception. I’ll admit, making caterpillars glow in the dark is just nerdy garden fun too.
The final categorization of Jessica’s top five garden predators is the lacewing. There are three groups of lacewings – green, brown and dusky wings. The dusky wings group spend most of their lives in trees, so they are less common in garden. Green and brown lacewings are very common, particularly in late summer.
These nocturnal insects have large, lace-like wings – hence the name. That unique characteristic makes lacewings easy to identify in your garden, and green lacewings are particularly beautiful.
Green lacewing eggs are easy to identify, because the adults lay eggs on stalks less than ¼” long. Why each egg is placed on a tiny stilt is still a mystery. It may be that the larvae are so voracious that they would eat each other, so isolation is a protection mechanism. Science still isn’t certain, but one thing we do know is that the adults are most attracted to dill and fennel. These plants are a great nectar source, but they are also the preferred egg-laying location of choice.
Lacewing adults are pollinators, feeding mostly on pollen and nectar. As with the fly and wasp beneficials, it’s the larval stage of lacewings which will attack garden pests. Lacewing larvae eat a variety of pests, but they are known as “aphid lions.” One lacewing can eat up to one hundred aphids every day.
Designing the Good Bugs Into Your Garden
Now that you have a better understanding of what to look for, how do you increase the predator population in your garden? Although many – if not all – of these good bugs are already present, there are easy steps you can take to protect and encourage them and naturally reduce pest problems.
- Incorporate the right plants – Many of these beneficial insects need shallow, exposed nectaries as adults. Flowers in the daisy family – like yarrow and coreopsis – are good examples. Members of the carrot family are also great options to promote those garden predators – look for dill, fennel, parsley, and other umbrella-shaped flowers. These are all important food sources for adults and can be the habitat adults prefer to lay eggs. By attracting adults and protecting their offspring, you are developing a mighty bug army which will keep pests at bay with little or no interference from year to year.
- Stop using pesticides – All pesticides, even organic options such as horticultural oils, can negatively impact garden predators. When a pesticide is deemed safe for certain insects, that designation is specific to adults. Those products haven’t been tested on the eggs or critical parasitoidal larvae. By applying something you think is safe, there’s a very good chance you are killing the next generation of garden warriors.
- Let the garden be a little messy – As gardeners, we often feel the need to keep things neat and tidy. We carefully groom our plants throughout the growing season and clean up garden debris in fall. Yet, insects often need plant litter as shelter or food. This is particularly true during cold winter months. Many pollinators and other bugs overwinter in plant debris. By allowing plant material to remain through those cold months, you are giving beneficial insects protection during hibernation. Wait to clean up your garden until temperatures reach into the 50-degree fahrenheit range, and those insects will be ready to emerge.
- Have diversity in the garden – Insects need food sources and shelter with different types of foliage, at different times of year, at different heights, etc. When you mix diverse plants together, you bring layers of color, shapes, sizes, varieties, and textures – which means a greater diversity of garden predators too. A greater diversity of predators in your garden, means fewer pest problems.
Think diversity in your plant location too. It isn’t necessary to grow all your tomatoes in one place. If you intersperse them with dill or fennel or asters, you will be distracting pests and encouraging beneficials to mill about and do their pollinating and predatory business.
For example if you struggle with rose thrips – place plants like oregano, wild mustard or daisies around your roses to attract the minute pirate bugs or lacewings which will feed on those thrips.
It’s not about ignoring the pests in your landscape – it’s about designing the pests out of and the beneficials into the garden (or just different areas of the garden).
- Don’t buy beneficials to release them – This still surprises many gardeners. Buying beneficials fits right into our “instant gratification” mentality. Yet, buying bugs can do more harm than good. Ladybugs available for purchase have been vacuumed during hibernation from the Sierra Nevada mountains. Since they are wild caught, they may be carrying diseases or pathogens which can infect any ladybugs native to your area. These ladybugs rarely remain where they are released, so they don’t provide much benefit to your garden anyway.
Purchased praying mantis are a Chinese species, which is not native to North America and which will outcompete native praying mantis. Praying mantis also prey on flying insects. In other words, their preferred food sources are pollinators and birds. That’s right, birds. Praying mantis can take down hummingbirds and other small species.
So rather than importing more trouble, support the beneficial bugs which are indigenous to your area by being thoughtful with your plant choices. Learn how to identify when the good bugs are present and in action. Before you squish, spray or remove a bug from your garden; consider allowing a little more time for the natural predator/prey cycles to take effect.
Remember too that this doesn’t need to be an all-or-nothing methodology – this can be your own evolution. You can pick one or two of these action steps to implement in your garden and go from there. Whether your garden is large or just a few containers on a balcony, every little bit you do will help. If you are willing to tolerate a little damage and take a proactive approach in plant diversity, your garden predators can be a powerful ally in pest management.
If you haven’t already listened to my conversation with Jessica, you can scroll to the top of this page and click the Play icon in the green bar just under the title. You’ll hear Jessica describe the singing habits of one garden predator as well as a few fascinating facts about aphid reproduction.
Links & Resources
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