Beneficial Insects in the Garden

What Are Beneficial Insects?

The average backyard is home to thousands of insects, but you may be surprised to learn that only about a tenth of these are destructive. In fact, most are either beneficial or harmless. Beneficial insects fall into three main categories:

1. Pollinators: We depend on these insects—including bees, butterflies, flies, and moths—to pollinate our garden’s flowers.
2. Predators: These insects eliminate pests by eating them. Things like ladybugs, praying mantids, and green lacewing larvae fall into this category.
3. Parasitizers: Like predators, parasitizers also prey upon other insects, but in a slightly different way. They lay their eggs on or in the bad bugs, and when the eggs hatch, the larvae feed on the host insects. Parasitic wasps are the main member of this category.

Meet the Beneficial Bugs in Your Backyard

Everyone knows their bees from their butterflies, but what about the many other beneficial bugs? It’s likely that you’ve already seen these good guys in your garden, but maybe you weren’t formally introduced. Here are a few you might want to become acquainted with:

Ladybugs

Despite their delightful name and appearance, ladybugs are ferocious predators! Before they get their bright red colors, they start out life as larvae (pictured below), cruising around on plants and feasting on aphids. Did you know that a ladybug larva can eat up to 40 aphids an hour?

Ladybug larva

Green Lacewings

Adult green lacewings feed on pollen and nectar, but their larvae, which look like a mix between a slug and an alligator, prey upon soft-bodied garden pests, including caterpillars and aphids.

Adult green lacewing

Praying Mantids

A praying mantis will make short work of any grasshoppers that are troubling you; these fierce predators will also hunt many other insect pests that terrorize gardens, including moths, beetles, and flies. Note, however, that praying mantids are ruthless and will also eat other beneficials, like butterflies, bees, and hummingbirds—and even each other!

Praying mantis

Spiders

Spiders—though technically arachnids rather than insects—are often overlooked as beneficial, but they are very effective pest controllers. Since they are attracted to their prey by movement, they eat many live insects. Jumping spiders and wolf spiders (pictured) are especially good at keeping pests under control.

Wolf spider

Ground Beetles

“Ground beetles” is the name of a large group of predatory beetles that are beneficial as both adults and larvae. They will eat a wide range of insects, including nematodes, caterpillars, thrips, weevils, slugs, and silverfish. While insects like Japanese beetles should be controlled in the garden, don’t crush every beetle you see!

Ground beetle

Soldier Beetles

Soldier beetles are an important predator of Mexican bean beetles, Colorado potato beetles, caterpillars, and aphids. Like many beneficials, they are attracted to plants that have compound blossoms, such as Queen Anne’s lace and yarrow.

Red soldier beetles

Assassin Bugs

Assassin bugs look like a strange mix between a praying mantis and a squash bug. They use their sharp mouthparts to prey upon many different types of insect pests in the garden. In their adult form, they can be mistaken for squash bugs, so look carefully before you squish something!

Assassin bug nymph feasting on prey.

Robber Flies

With their extra-long legs, robber flies are bug-eating machines that we’re thankful to have on our side. They may look intimidating, but unlike horseflies, they do not attack humans (although they are capable of biting when threatened). Instead, they go after a number of common garden pests. Try not to shoo this fly!

Robber fly with prey.

Hoverflies

Another good fly to have in your garden, the hoverfly looks like a tiny yellowjacket without a stinger. They feed on pollen and nectar and are extremely important pollinators. Their larvae are voracious predators, killing aphids, caterpillars, beetles, and thrips by sucking the juice from their victims.

Hoverfly

Parasitic Wasps

Parasitic wasps are very tiny, so you probably won’t see them at work. However, they are a very effective pest control.

• Brachonid wasps lay their eggs on the backs of tomato hornworms and other caterpillars, forming those white cocoons you see on the caterpillar’s back (pictured below). If you see a parasitized caterpillar, don’t kill it. Instead, move it to elsewhere in your garden. The wasp larvae will take care of them for you and turn into more wasps, who will continue to do their good work in your tomato patch.
• Trichogramma wasps are minuscule wasps (several of them can fit on the head of a pin) that lay their eggs inside the eggs of over 200 different insect pests, preventing the pests’ eggs from ever hatching in the first place.
• The tachinid fly looks like just a small housefly, but is an active parasitizer of corn borers, gypsy moth caterpillars, grasshoppers, Japanese beetles, Mexican bean beetles, squash bugs, and green stinkbugs.

Parasitic wasp eggs on a hornworm.

Attracting Beneficial Insects

Like all living creatures, beneficial insects have a basic need for water, food, and shelter. By providing these things, your garden will become an inviting home for them.

A diversity of plants will attract a wide range of insects. Many beneficials appear in the garden before the pests do and need alternative food sources such as pollen and nectar if they are to stick around.

• Early-blooming plants, especially ones with tiny blossoms like alyssum, or biennials such as carrots or parsley that have been left to bloom, will help draw beneficials to your yard in the spring.
• Later, they will be especially attracted to plants with compound blossoms such as yarrow, goldenrod, and Queen Anne’s lace and flowering herbs like lavender, mint, sage, dill, fennel, and lemon balm.

Remember that if you resort to using chemical pesticides to control insects, you will often kill good and bad bugs alike. Even the so-called “natural” pesticides like pyrethrum and rotenone will kill many beneficial insects.

In her book Green Thoughts Eleanor Perenyi writes, “Every insect has a mortal enemy. Cultivate that enemy and he will do your work for you.”