How do predaceous insects help the garden?

September 20, 3:32 PMPittsburgh Gardening Scene ExaminerRose Field

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While novice gardeners may be unfamiliar with the label “predaceous insects”, chances are they have long been familiar with some of the insects bearing the label. Ladybugs and praying mantises are well-known to everyone, gardener and non-gardener alike. Their practical value comes to light when we examine their predatory nature and how it can work for our benefit in an organic garden. These, along with many other lesser-known species, are predators in the insect world, hunting and killing other insects for food, often preying on pests that plague our fruits, vegetables and ornamental plants.

Long before chemists invented lethal bug sprays, nature devised a wonderful system of checks and balances. Dragonflies eat mosquitoes, spiders eat a wide range of pests. Green and brown lacewings are called “aphid lions” due to their appetite for the plant pests. Houseplant enemies such as aphids, scale and mealybugs are food for ladybugs. The Ichneumon wasp, which is harmless to humans, eats the European corn borer. The list goes on and on.

One of the major drawbacks of chemical pesticides is the indiscriminate nature of the toxicity. Praying mantises and ladybugs, bees and even birds, die along with the aphids and cutworms. Predatory insects are much more targeted in their killing.

A useful pdf document from the Michigan State University Extension points out important principles of pest management utilizing predaceous insects. One salient point:

“Because natural enemies depend on the pest for development, a certain population level of the pest is necessary to sustain them.”

We have been conditioned to expect perfection by the purveyors of the perfect lawn, the perfect apple and the perfect rose, but this fake cosmetic perfection comes at a price and is usually purchased with poison. If we can learn to live with a small number of aphids instead of demanding zero tolerance, the lady bugs and green lacewings will be attracted to live in our garden and keep the pest population low.

Another pdf document with an excellent overview of all aspects of organic gardening is available from Purdue University, and it provides good tips on attracting beneficial insects, pointing out that an ample supply of nectar and pollen throughout the growing season is important. Clover, marigolds and zinnias work  well to provide this.

Also check the Cornell gardening resources “Attracting Insects' Natural Enemies” for tips on attracting “good bugs.”

The Planet Natural store website shows good pictures of useful predatory insects. However, as the Purdue article points out, buying these predators is often unnecessary, and they can simply leave after you release them. Planet Natural offers 250 eggs of the spined soldier bug for sale for $118.95. Most folks in our area have all the spined soldier bugs, also commonly known as "stink bugs",  they can handle. These slow-moving little tank-like critters invade our houses in the fall to over-winter. While they're harmless, unless you squash them and have to endure their smell, they are certainly more welcome outdoors than in. Welcome or not, they teach us a lesson: be careful what you kill.

For More information about natural controls see articles on

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