Only a few of the world’s 750,000 known insects are worthy of the label ‘pest’. Most are harmless, some are beneficial to your garden, and they all have a role to play. So the next time you spot an unfamiliar critter in your garden, consider it innocent until proven guilty. Beneficial insects provide a number of essential services including pest control, pollination and the breakdown of decaying matter.
Attract and Protect
Beneficial insects will help you attain great garden success. Follow these guidelines to attract and protect a diversity of garden allies:
- Fill a shallow birdbath or dish with stones and water so tiny beneficial insects can drink without drowning.
- Attract adult insects with a variety of nectar and pollen-rich plants including herbs (e.g., fennel, dill and parsley) and flowers of the daisy family (e.g., cornflower, coneflower, sunflower and coreopsis).
- Leave some weeds in your yard including lamb’s quarters, Queen Anne’s lace and dandelion for food and shelter. Dandelions are especially important as they play a part in the ecology of 93 different insect species.
- Avoid chemical and botanical insecticides that kill good insects with the bad. If you must use these products, spot-spray instead of broadcast spray.
- Plant hedges and windbreaks to protect beneficial insects from dehydrating dust.
- Minimize tillage to protect the habitat of soil insects and animals.
- Establish permanent walkways and perennial beds, apply mulch and allow some leaves to remain where they fall for year round shelter.
- Top-dress lawns and gardens with finished compost to enrich soil life.
The Usual Suspects
Here is a list of beneficial insects commonly found in gardens. The larval (immature) form of most of these species differs greatly from the adult form. Familiarize yourself with the appearance, diet and shelter requirements of all life stages.
Ladybugs (Ladybird Beetles)
Adults range in colour from pale yellow to red to black and are often spotted. 
They are attracted to angelica, tansy and scented geraniums. Larvae look like spiny alligators. Both adults and larvae feed voraciously on small, soft pests such as aphids, mealybugs and spider mites.
Lacewings
The pale green or brown, alligator-like larvae prey on aphids, scale insects, small caterpillars and thrips. Adults have large, finely veined wings and feed mainly on flowers including Queen Anne’s lace, wild lettuce, goldenrod and tansy. Stratford Camera Club
Parasitic Wasps
Adults of these mostly tiny and non-stinging wasps are attracted to members of the carrot 
and daisy families, strawberries and clover. Females inject their eggs into or onto pests such as aphids, flies, beetles and many caterpillars. Larvae grow by absorbing nourishment through their skin. See Common Garden Pests (Caterpillars).
Tachinid Flies
These large, bristly, dark grey flies place their eggs on cutworms, sawflies, stinkbugs and other pests. Adults are attracted to pollen and nectar plants including bee balm, comfrey, rudbeckia and butterfly bush.
Aphid Midges
Delicate, long-legged adults feed on the honeydew left by aphids. Larvae, which look like tiny orange maggots, voraciously consume aphids.
Syrphid Flies
Also known as hover flies, these black-and-yellow- and black-and-white-striped flies resemble wasps, but do not have stingers. They are attracted to bee balm, butterfly bush, marigold and members of the daisy family, and are highly effective pollinators. Females lay their eggs in aphid colonies. The greenish-grey larvae that emerge eat aphids in tight places too small for most other insects.
True Bugs
This is the common name for insects in the Hemiptera order. Members of this order have needle-like beaks for sucking fluids and leathery wings crossed flat over their backs. Immature insects closely resemble adults. While some are garden pests, many others are allies. Assassin, ambush and minute pirate bugs prey on the tomato hornworm, thrips, leafhopper nymphs, corn earworms and a great number of other pests.
Ground Beetles
These large, iridescent black beetles hide under rocks and logs during the day and move 
quickly when disturbed. They live in the soil and eat a variety of pests including slugs, snails, grubs, cutworms and root maggots. They are attracted to perennial groundcovers, logs and stones.
Spiders
Although not insects, spiders are often grouped with them. Some of the best predators in the garden, spiders catch their prey in webs or leap on their prey using silk thread as a dragline. Common garden spiders do not move indoors come fall and are nonpoisonous.
Earthworms
Earthworms — also not insects — are highly beneficial in gardens. Referred to as ‘nature’s plow’, earthworms aerate and enrich the soil. Worms are highly sensitive to chemical and physical changes, so avoid any synthetic fertilizers, and minimize tillage.
As you get to know the residents of your garden, you’ll find it’s an ever-changing delight to take time to stop and look, to see who’s at work today, to observe the ones who have been working all week, and to welcome the new helpers. When autumn comes, check out Putting The Garden to Bed for ways to keep those helpers coming to your special garden.
Reprinted & adapted with permission of the Toronto and Region Conservation Authority
See also: Gardening for Wildlife and Plants That Attract Beneficial Insects to the Garden
Learn more about the insect world by exploring resources at the Stratford Public Library for additional information! 19 St. Andrew Street (519-271-0220)