In the garden, bugs have a bad reputation: We call them pests, curse them when we find our crops eaten and sometimes even consider poisoning them with chemical pesticides. Yet, more than 97 percent of insects and spiders in home gardens and landscapes are actually beneficial, says Leonard Perry, extension professor at the University of Vermont. “That is, they either do no harm, provide food for desirable species such as birds, or prey upon insects that are destructive to our crops,” Perry says.
When it comes to maintaining the health of our gardens without turning to hazardous chemicals, good bugs may be among our best allies. Knowing how to identify the most common beneficial insects, and how to help and not harm them in your garden, will help you minimize pest problems and the use of pesticides.
Understanding Good Bugs
There is a hidden world in and around our gardens that we can begin to understand if we employ patience, observation and a bit of hard science. In fact, the plant and insect life in our gardens is so deeply intertwined, scientists now know that some plants emit a chemical alarm signal when pest insects begin feeding on them, alerting nearby beneficial insects to respond. If your garden is fully stocked with beneficial bugs, they can become your pesticide-free pest patrol.
If we think about our gardens as whole ecosystems, rather than a collection of individual plant species, it can help us learn what causes insects to come to our garden in the first place, what incites them to stay and which ones we hope will do so. The first step is to learn about the life cycle of insects, and how this affects the natural balance.
Too often, gardeners wait until they have a problem, then try to combat the imbalance by ordering beneficial insects from a mail-order supply. This is unlikely to help solve the problem. Typically the new insects will eat then leave after a day or two. If we hope to maintain a supply of natural pest-killers, our goal is to attract and nurture beneficial insects long enough that they stay and lay eggs, hatching new generations of pest protection.
Another reason to keep beneficial bugs around to lay eggs is that adult insects eat far less than just-hatched hungry larvae. Take, for instance, Coccinellids, more commonly known as ladybug beetles, one of the best-known beneficial insects with more than 450 species native to North America alone. A single adult ladybug beetle (a term entomologists prefer, as these are not true bugs) will eat 50 aphids in a single day and lay hundreds of eggs. The young hatch, however, will devour thousands of aphids, mealy bugs, scales, spider mites, thrips, whiteflies and other slow-moving insects. Cultivating ladybug beetles in several lifecycle stages will be the most beneficial.
Attracting and Keeping Beneficial Insects
Cultivating the right type of plants plays a key role in attracting beneficial insects to make their homes in our gardens. Researchers have identified a few plant groups with flowers that easily provide nectar and pollen to insect friends: plants in the daisy family such as aster, cosmos and yarrow; plants in the carrot family such as cilantro, dill, parsley and fennel; alyssum and other members of the mustard family; mints; and buckwheats. As you select plants, keep in mind bloom time, aiming to provide sources of nectar throughout the growing season.
How we plant for beneficial insects is also key. Companion planting is a time-honored method of placing plants together to attract beneficial insects while deterring harmful ones. Roses, for instance, are susceptible to aphids; but underplanting roses with sweet alyssum attracts parasitic wasps that eat aphids. Nasturtiums and marigolds do the same thing for vegetable gardens, providing a colorful element while acting as a protector, drawing aphids away from tomatoes and other garden crops.
While interplanting can help protect specific plants, it’s also wise to plant a permanent space for beneficial bugs near your garden plants. This offers an undisturbed space for beneficial bugs to feed, reproduce and overwinter, ensuring you will keep your garden friends for multiple seasons. Mimic natural systems by adding borders or strips of diverse perennial vegetation, including flowers, shrubs and grasses. Make sure to research which plants are native to your area and include some of these natives in your plantings: Native plants are perfectly suited to coexist with native bug populations.
Finally, cover the soil with organic mulch or cover crops, which protect beneficial insects from climate extremes, and provide bugs with a source of water such as birdbaths or other shallow, gravel-filled dishes. (Make sure to change water often to avoid mosquitoes.)
The Best Offense
When it comes to naturally fending off garden pests, observing your garden closely is your most important task. Learn to check your garden often, carefully inspecting plant stems and the undersides of leaves for eggs and larvae, and learn which bugs—good and bad—are likely to call your garden home. We include a list of 10 of the most beneficial bugs below, but you might also consider investing in a dependable bug identification book such as Good Bug Bad Bug by Jessica Walliser.
Set up a bench and keep a watchful eye on the activity in your garden. Visit at different times of day, and simply observe the patterns of the insects coming to visit. Because there are so many more beneficial insects than harmful ones, it helps to try to identify which bad bugs are in your area. Notice foliage that is eaten or scarred. Sometimes when the insects are not evident, the type of damage to the plant can help you identify the type of insect that may be causing it. Make it a habit to check the underside of the leaves of plants that are susceptible to insects. If you see egg clusters, try to identify them; pest eggs will quickly hatch into hungry larvae that can strip the leaves and cut off nutrition to the plant. Sometimes, the best natural solution is to put on your garden gloves and squish the eggs before they have a chance to hatch.
Top 10 Beneficial Insects
1. Braconid Wasps (Hymenoptera): Nonstinging; less than 1⁄2 inch long; adults lay eggs inside or on host insects
Diet: Caterpillars (including tomato hornworms), flies, beetle larvae, leaf miners, true bugs and aphids; adults also consume nectar and pollen
2. Tachinid Flies (Diptera): Most resemble houseflies but with short, bristly hairs on the abdomen; all develop as internal parasites of other insects, including many garden pests
Diet: Larvae feed internally on caterpillars, beetles, bugs, earwigs and grasshoppers; adults feed on nectar, pollen and honeydew
3. Ground Beetles (Coleoptera): 1⁄8 to 1-1⁄2 inches long; dark, shiny and hard-shelled
Diet: Asparagus beetles, caterpillars, Colorado potato beetles, corn earworms, cutworms, slugs, squash vine borers and tobacco budworms
4. Predatory Bugs (Hemiptera): Includes big-eyed, minute pirate, assassin, damsel and predatory stink bugs; all use mouth, or “beak,” to pierce and consume prey; adults range in size from minute pirate bug (1⁄16 inch long) to large wheel bug (1-1⁄2 inches long)
Diet: Aphids, caterpillars, scale insects, spider mites and insect eggs; many also prey on beetles
5. Hover or Syrphid Flies (Diptera): Larvae are small, tapered maggots; black-and-yellow-striped adults resemble yellow jackets but are harmless to humans; hover like hummingbirds as they feed
Diet: Larvae eat mealybugs and small caterpillars, and are especially helpful in controlling early season aphids; adults feed on nectar and pollen
6. Spiders (Araneae): More than 3,000 North American predatory spider species include crab spider, jumping spider, wolf spider and orb-web spider
Diet: Depends on species but can include aphids, beetles, cutworms, fire ants, lacebugs, spider mites, squash bugs and tobacco budworms
7. Lacewings (Neuroptera): Larvae, sometimes called “aphid lions,” are 1⁄2 inch long and light brown with hooked jaws; adults are light green or brown and 1⁄2 to 1 inch long with transparent wings
Diet: Larvae eat aphids, small caterpillars and caterpillar eggs, other larvae, mealybugs, whiteflies and more; adults eat honeydew, nectar and pollen; some eat other insects
8. Soldier Beetles (Coleoptera): Elongated, 1⁄2 inch long beetles with soft wing covers; larvae are brown and hairy; adults usually have yellow or red and black markings and resemble fireflies
Diet: Larvae feed on eggs and larvae of beetles, grasshoppers, moths and other insects; adults feed on aphids and other soft-bodied insects, as well as on nectar and pollen
9. Trichogramma Mini-Wasps (Hymenoptera): Lay eggs inside host’s eggs, where trichogramma develop as internal parasites; life cycle is seven to 10 days from egg to adult so populations can grow rapidly
Diet: Pest eggs, especially those of cabbageworms, codling moths, corn earworms, diamondback moths, and other moths and butterflies
10. Ladybug Beetles (Coleoptera): 1⁄4 inch long; larvae can resemble tiny alligators, and are usually dark and flecked with red or yellow; adults are rounded with orange or red bodies with black spots
Diet: Larvae and adults both dine on aphids, small caterpillars, small beetles and insect eggs; specialist species feed on scale insects, mealybugs, mites and even powdery mildew; adults also eat honeydew, nectar and pollen