Of the millions of species of insects in the world, few are actually harmful to garden plants. In fact, many species, known as beneficial insects, support gardens by feeding on particularly harmful insects.
What Are Beneficial Insects?
Beneficial insects are the species of insects that support the health of plants through either pollination or pest control.
It’s possible to encourage beneficial insects to reduce the harm of nuisance insects without resorting to chemical sprays, which can kill both nuisances and beneficial insects alike.
While honeybees, bumblebees, and butterflies need no introduction, other insects—predators rather than pollinators—may be less familiar. “Pollinators get a lot of press,” Becky Griffin, school and community garden coordinator for the University of Georgia’s College of Agriculture, told Treehugger. “But if you’re gardening to take care of your pollinators, go ahead and start taking a closer look, because you are going to be attracting all sorts of beneficial insects as well.”
Here are 14 beneficial insects you want to start attracting.
Red Paper Wasp (Polistes spp.)
Red paper wasps are parasitic wasps with red bodies and black wings. These wasps reduce the presence of caterpillars, aphids, scale insects, and whiteflies. They help control pests by paralyzing them and laying eggs inside them. To be able to do this, parasitic wasps must be small, usually only an eighth of an inch to a half-inch long.
Pollen-producing flowers like asters, tansy, chamomile, fennel, and caraway in or near your vegetable garden attract red paper wasps and then help to keep their offspring around.
Lady beetles (Family Coccinellidae)
Lady beetles are better known in North America as ladybugs and in Great Britain as lady birds, but they are beetles. They are popular with gardeners because they feast on aphids, scale insects, mites, fruit flies, thrips, and mealybugs. Garden centers may sell ladybugs in cartons or netted containers. Adult ladybugs can eat thousands of aphids over a lifetime, but they also lay eggs in aphid colonies so that their larvae will immediately start feeding once they emerge.
Imposters such as the Mexican bean beetle (Epilachna varivestis) can be mistaken for ladybugs because they are yellowish orange with black spots, like some true ladybugs. Unfortunately, these are agricultural pests that feeds on snap beans and lima beans. The easiest way to tell the difference is location: as their name suggests, Mexican bean beetles will be found on beans, not flowers.
Because ladybugs can fly, there is no guarantee that they will remain in your garden for long, but they do overwinter once aphids begin to disappear, so there is a likelihood that they will remain in the same area and visit your garden the following spring.
Keep ladybugs around by planting nectar-producing plants like tansy, milkweed, and scented geraniums.
Tachinid Flies (Family Tachinidae)
Tachinid flies are the most abundant of parasitic insects, with over 1,000 species in North America. Many have been imported from other parts of the world for insect control, such as the red-eyed fly. many species feed on scale insects, caterpillars, and beetles in both larval and adult stages. Others feed on sawfly larvae, grasshoppers, earwigs, and other bugs.
Many Tachinid flies resemble ordinary household flies, except that they are slightly larger. Others look like bees or wasps. They can be gray, black, or striped, with distinctive abdominal bristles.
You’ll find adult tachinid flies visiting flowers, posing on foliage awaiting the appearance of their prey. Avoid broad-spectrum insecticides if you want to attract them to your garden.
Ground beetles (Family Carabidae)
There are thousands species of ground beetles, many that are beneficial to your garden. Most hunt at night, so you may not notice them during the day unless you flip over a rock.
Given their diversity, ground beetles can take care of a number of garden pests like snails, slugs, and cutworms. Calosoma sycophanta, pictured here, devours gypsy moth caterpillars.
Ground beetles can be brown, black, or metallic green or blue in color. Don’t confuse Calosoma sycophanta with a Japanese beetle, a nuisance in many a garden.
Ground beetles live in mulch, leaf litter, rotting wood, and other decaying plant matter. During the day they’ll hide under stones or other solid structures in the garden. They will overwinter among perennials as well. You can also plant cover crops like clover to attract ground beetles.
Lacewings (Family Chrysopidae)
While adult lacewings feed only on nectar and pollen, they lay their eggs around infested plants so that their larvae will eat thousands of aphids, scale, spider mites, mealy bugs, caterpillars, whiteflies, and thrips. Adults can be green or brown with their transparent wings showing a distinct network of veins. Their larvae resemble alligators, with oblong, soft bodies and distinctive sickle-shaped lower jaws. They often hide under debris and surprise their prey.
Lacewing larvae and eggs are commercially available. The eggs are shipped ready to hatch and start feeding. They can be sprinkled onto your plants or planting bed. Larvae are shipped in a honeycomb to separate the larvae from eating each other. They can be released directly onto plants.
Unfortunately, they can emit a foul odor when handled, so use caution. Apply the eggs or larvae periodically to continuously keep both vegetables and ornamental plants healthy throughout the course of the growing season.
Since adults feed on nectar and pollen, keep lacewings in your garden by planting roses, marigolds, scented geraniums, or a commercially available supplemental food source which you can spray on your plants.
Damsel bugs (Family Nabidae)
Damsel bugs are native throughout all of North America. They are slender and elongated and may be cream-colored, dark brown, or black. They are most active in mid-summer, eating a wide variety of insects, including caterpillar eggs, thrips, aphids, spider mites, and fleahoppers.
Damsel bugs are attracted to many commercial crops like clover, alfalfa, soybeans. They can also appear in backyard gardens.
Since damsel bugs will overwinter on site, plant a cover crop or flowering plants with winter interest to give them shelter and places to hide.
Assassin bugs (Family Reduviidae)
Nearly 200 species of assassin bugs are native to North America. They are predatory insects that feed on a wide variety of insects, including flies, beetles, and caterpillars, by ambushing their prey, piercing the victim’s body with a short three-segmented beak then sucking out bodily fluids.
Assassin bugs move slowly and are generally oval-shaped or elongated with a long and narrow head. They are usually black, orange-red, or brown. Avoid handling them, as they can defend themselves with a painful bite from their proboscis. They emerge in June and stay throughout the summer.
You can attract assassin bugs by avoiding pesticides, installing garden lights like solar-powered ones, and planting marigolds, dandelions, sunflowers, Queen Anne’s lace, daisies, goldenrod, alfalfa, and various herbs like dill and fennel. They also like to hide in mulch, lawn clippings, or leaf piles in order to ambush their prey.
Two-spined soldier bugs (Podisus maculiventris)
The two-spined soldier bug is a common North American predatory stink bug that preys on more than 100 pest species like caterpillars and beetle larvae, including many that infest a wide variety of vegetables. Their favorites include the Mexican bean beetle, the Colorado potato beetle, and the cabbageworm. In the adult stage, its body is light brown and shield-shaped.
Many stink bugs are nuisances, and gardeners should be aware that a mature squash bug (a garden pest) resembles the two-spined soldier bug, but the two-spined solder-bug does little damage to crops. Says Nancy Griffin: “If you see a bug that looks like the two-spined soldier bug on your squash or pumpkins, the chances are that it’s a squash bug and not a good bug.” Squash bugs suck the sap out of plants.
To keep two-spined solder bugs around, avoid non-selective insecticides. Adults will overwinter in place, so keep leaf litter or mulch around to give them a place to shelter.
Garden spiders (Order Araneae)
Spiders need little introduction. Unlike humans, spiders don’t discriminate between beneficial and nuisance insects. They are generalists when it comes to prey, as they will eat whatever falls into their clutches.
While many spiders spin webs and await unsuspecting victims to get stuck in them, other spiders sit still and ambush their prey, while still others are active hunters.
Attracting spiders to your garden isn’t hard. Give them protection from the elements, such as mulch, grass clippings, or leaf litter. And as always, avoid non-selective pesticides. Outdoor lights are also effective, as many spiders spin their webs around them to trap other insects attracted to the light.
Praying mantis (Mantis religiosa)
Praying mantises are very recognizable, distinctive-looking predators whose front legs have sharp spines to seize their prey, which include insects such as flies, crickets, moths, grasshoppers that harm crops as well as spiders, lizards, frogs, and even small birds.
Mantises will eat any but that they can catch, so you’ll lose other beneficial insects to them as well as nuisances. They are less voracious than other predatory insects, so losses of beneficial insects will be minimal—but so will losses of nuisances.
A healthy, diverse flower or vegetable garden of native plants is the best way to attract mantises. Mantises will be killed off by a frost, but in some areas they will overwinter in a garden plot, so to give them a place to shelter, it’s recommended to not prune back or remove dead plants until spring.
Dragonflies (Order Odonata)
Dragonflies rely on water to reproduce, as female dragonflies lay eggs on the water’s surface or sometimes insert them into aquatic plants or mosses. Dragonfly larvae will eat mosquito larvae (also water-born) and help keep mosquito populations under control.
Adult dragonflies have four sets of wings and an ability to operate each wing independently. That makes them excellent fliers, which is important because they catch all their prey with their legs while in flight. Their diet consists of numerous insects, including pests, such as mosquitoes and midges as well as butterflies, moths and even smaller dragonflies.
Unless you live near freshwater, you’re not likely to see many dragonflies in your garden. Attempting to attract them with pools of standing water in your yard is more likely to breed mosquitoes than it is to breed enough dragonflies to keep them under control.
Syrphid flies (Sphaerophoria spp.)
Syrphid flies are also known as hoverflies. They get that name from their ability to hover like tiny helicopters in your garden and from the ability to fly backwards, something highly unusual in the insect world. In the larval stage, they feed on pests such as aphids, scale, thrips, and caterpillars. As adults, they help control aphids and act as pollinators on flowers as they hover over them.
Many species look like bees, but syrphid flies have large eyes that cover most of the head, and have only two wings, while wasps and bees have four.
Planting a variety of pollen-producing flowers will attract syrphid flies, as they feed primarily on pollen, nectar, and aphid honeydew.
Robber flies (Order Diptera)
A robber fly is a medium-to-large, stoutly built fly that’s sometimes called an assassin fly. This is an aggressive predator that will attack yellow jackets and hornets, the kinds of things other insects avoid. Because of that, they are considered a beneficial insect.
However, they are not choosy and will attack pollinators such as bees, even if the bee is larger than they are. They catch their prey by ambushing them in mid-air, kill their victims by paralyzing them, then eat them by sucking out their insides.
A defining characteristic of these unique-looking, hump-backed insects is a distinctive hollow space between their large compound eyes.
A loose mulch of wood chips or leaf litter will help attract robber flies, as their larvae live in soil, wood and other habitats, feeding on organic matter.
Earwigs (Order Dermaptera)
There are many different earwig species in the United States—and they come with a bad reputation, including some erroneous ones. (No, they don’t invade people’s ears.) Earwigs can be a nuisance in their own right, especially if they appear in large numbers or invade a home, even if they are mostly harmless.
But many species of earwigs eat mites, aphids, nematodes, slugs, and a wide variety of nuisance insects in the garden. Most are omnivorous, and will just as likely feed on the tender shoots of plants as on insects. But only if they amass in large numbers will they be a threat to your garden.
Earwigs are dark brown to black in color, with glossy backs, long antennae, and their trademark pincers at the end of the abdomen.
Earwigs are drawn to moisture, so they like to hide in wet leaf litter, mulch, or anything lying around the yard that might trap moisture. Keep earwigs in your garden and away from your home by spreading dry gravel around the house’s foundation and keep leaf litter away from it.
How to Support Beneficial Insects
In a healthy ecosystem, there is neither beneficial insect nor nuisance, since predator and prey are in harmonious balance with each other. The more your landscape is populated with a diversity of native plants, the healthier, more ecologically balanced it will be.
Plant perennial flowers that bloom early in spring to provide food for hungry beneficial insects emerging after winter. Plant long-blooming annuals that produce lots of nectar for much of the growing season. Intersperse flowers and vegetables. Plant a low-growing tree for bug-eating birds to perch as they hunt for prey. A healthy, diverse garden means is a sustainable one where you will have to rely less on attracting beneficial insects to combat the nuisances.