Beneficial Insects in the Garden

Ahealthy garden abounds with insect life–and, as gardeners, it's helpful to know which insects are working with us rather than against us. It can be frustrating to spend time and money on plantings only to watch them be devoured by pests like flea beetles, tomato hornworms, and aphids. Rather than resorting to pesticides, though, the first line of defense should be getting out to the garden regularly to monitor plants for damage and to learn to distinguish between friend and foe. Handpick eggs, larvae, and adults of pests whenever possible and keep your plants well-fed and watered (so that they can mount their own natural defense). Use row cover to protect crops from cabbage worm, cabbage looper, flea beetles, onion maggots, thrips, and early season cucumber beetles. However, the most effective pest-prevention strategy of all may be to grow a wide variety of plants that support beneficial insects. 

Beneficial insects include pollinators (such as bees, flies, butterflies, and moths), predators (like lacewings, preying mantids, and ladybugs), and parasitizers (such as brachonid wasps and tachinid flies). Parasitic wasps are very tiny and generally don't sting people. Preying mantids are somewhat indiscriminate in their appetite but can help get pest populations down. Spiders are beneficial predators too, although these are arachnids rather than insects. Growing a diversity of plants creates the necessary habitat for beneficial insects to complete their lifecycle and go to work for you. Learn to identify the insects in your garden at every stage of their development: many beneficial insects are most effective in their larval stage, such as aphid lions (lacewing and ladybug larvae). A garden teeming with life is a beautiful sight! Here are just a few of the many beneficial insects that you can find in a healthy garden:

Swallowtail butterflies aren't just pretty–they're effective pollinators! Plant Dill, Fennel, Carrot, and Parsley and welcome a little nibbling from the swallowtail caterpillar. Dill also attracts lacewings, braconid wasps, and mealy bug destroyers.

Smaller beneficials, like hover flies, feed upon the nectar of Dara Daucus and other umbel shaped blooms of the carrot family. Hover fly larvae feed upon aphids, thrips, scale, and pest caterpillars. 

Ladybugs and their larvae are fierce protectors of the garden! A single ladybug can eat up to 5000 aphids in its lifetime. Calendula draws ladybugs, honeybees, bumblebees, and lacewings.

Tiny, non-stinging parasitic wasps help to control cabbage worms, tomato hornworm, squash vine borers, and more! Plant Yarrow to invite these and other beneficials.

Assassin bugs feed on cabbage looper, flea beetles, aphids, and other garden pests. Some assassin bugs like Marigolds, including Mexican Mint Marigold shown here, in addition to Fennel and Dill. 

Dragonflies are skilled predators, feeding on mosquitos, gnats, small moths, and midges. Grow Swamp Milkweed (great for clay soils) to provide a dragonfly hunting ground.

Hosts for tachinid fly larvae include cabbage looper, corn borer, potato beetle, and squash bugs. The adult fly is an excellent pollinator as well. Feverfew draws tachinid flies and hover flies.

Bumblebees are gentle giants among bees and prolific pollinators. Plant Blue Sage (shown here) and Common Sage to invite more bumblebees into your garden.

Lacewings aren't picky: They'll happily munch mealybugs, mites, thrips, aphids, and leafhoppers. Cosmos and Coreopsis feed adult lacewings and their aphid-eating larvae.

To learn about beneficial insects, visit this helpful brochure from the Cornell Cooperative Extension. For help identifying the insects in your garden, at every stage of their development, visit the Bug Guide