How to manage insects in the garden

ladybug on leaf

You may be convinced that all insects are bad, but that’s not true, especially in the garden.

There are plenty of insects that are beneficial to the plants and flowers in your garden. Good insects help to control the number of bad insects that destroy plants.

Good bugs

The following list of good insects that you may find in your garden is adapted from Penn State University Extension and University of Nebraska-Lincoln Extension:

Ladybugs. Both the immature and mature beetles have benefits for your garden. The immature beetles feed on aphids, scale insects, mites, mealy bugs, whiteflies, thrips and the eggs of other insects. Immature ladybugs look like tiny alligators; they usually have orange or yellow spots, but they don’t look like mature ladybugs. Mature ladybugs will eat aphids.

Ground beetles. Ground beetles eat other types of insects. They’ll eat caterpillars, cutworms, root maggots, spiders, mites and other beetles.

Hover flies. Hover flies have yellow and black markings, so they’re often mistaken for wasps or bees. However, hover flies can’t sting. Hover fly maggots are predators. They are pale, greenish brown in color. They eat aphids, leafhoppers, scale insects, mealybugs, thrips and corn borers (corn earworms).

Parasitic wasps. Parasitic wasps live inside small insects, while some live inside insect eggs. When adult parasitic wasps mature, they eat their hosts. Some parasitic wasps are small and difficult to identify as wasps.

Spiders. Spiders offer control of grasshoppers, crickets, moths, true bugs and other insects.

Praying mantis. Mantids prey on many different insects.

Assassin bugs. Assassin bugs attack and kill their prey. They aren’t poisonous but will bite, so it’s a good idea to leave them alone if seen.

Damsel bugs. Damsel bugs will feed on grasses and ground cover in gardens. They’re long and slender with large forelegs and slender back legs.

Lacewings. Lacewings can eat 200 insects a week. Green lacewings are more prevalent in lawns and gardens than brown lacewings.

Ant lions. Ant lions will capture ants and small insects during the night.

Tachinid flies. Tachinid flies are parasitic and invade their hosts internally.

Attracting good insects

Penn State University offers directions for building a ‘good bug tub’ for your garden. As the name suggests, the plants in the tub will attract good bugs. It can be made out of galvanized metal or plastic, have a capacity of about 18 gallons and should have drainage holes drilled in the bottom. The tub can be placed on casters so that it can be moved easily.

The tub should be filled with a mixture of potting soil, compost or commercial potting soil. Fertilize the soil weekly, or use a time release fertilizer.

Some of the plants that can be used in the good bug tub include dill, basil, nasturtium, sweet alyssum and yarrow. Each plant will attract specific good bugs.

Bad insects

The following list of common bad garden insects is adapted from Purdue University Extension. For information about other common bad garden bugs as well as ways to control them, refer to Purdue’s Vegetable Insects publication.

White grubs. Some white grub species eat roots or the underground parts of most vegetables.

Wireworms. Wireworms target corn, bean and pea seeds and seedlings. They’ll also eat potatoes, sweet potatoes, radishes, carrots, rutabagas and turnips. Wireworms will eat the roots of cabbage, cucumbers, tomatoes, onions and watermelons.

Cutworms. Cutworms feed on most vegetables in the garden. They usually feed on young plants low to the soil’s surface, but they may also climb the plant to feed on foliage and fruit.

Japanese beetle. Japanese beetles feed on a variety of plants and tend to reinvade yards and gardens, even after the areas have been treated.

Tarnished plant bug. Tarnished plant bugs typically feed on beans, beets, chard, celery, potatoes, cabbage, cauliflower, turnips, salsify and cucumbers. These pests are active early in the season and can migrate to preferred plant hosts.

Blister beetles. Adult blister beetles feed on plant leaves.

Aphids. Aphids are normally found on the underside of leaves and are usually in large clusters. They suck on leaves and cause them to turn downward.

Twospotted spider mites. Mites aren’t insects, but they remove plant juices from bean, corn, tomato and eggplant leaves. Mites are typically a problem in hot, dry weather.

Slugs. Although they’re not classified as insects, slugs will shred plants leaves or defoliate entire plants. Slugs normally are a problem in cool, wet weather.

Tips for keeping bad insects out

Purdue University Extension offers helpful tips for decreasing the number of harmful insects in your garden:

  • Remove plant residue from the previous year’s garden.
  • Pay attention to recommended varieties for your area as well as recommended planting times.
  • Inspect transplants to make sure they aren’t infested with insects.
  • Properly space plants, use appropriate fertilizer and water to ensure healthy plants.
  • Weed frequently.
  • Regularly inspect plants for insects or insect damage.
  • When pests are observed, treat most vegetables with insecticides. Plants like cucumbers, cantaloupes and squash should be treated before damage is detected as a preventative measure.

More about garden insects:


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