Beneficial Bugs

Green lacewing on peony bloom

Q: I know there are “good” bugs and “bad” bugs for my garden. How do I know which is which?

A: Insects – a general term for “multi-legged creepy crawlies” have a certain “ick” factor for many people. In spite of their tiny size, we perceive them as scary and harmful to people. Surprisingly, most insects found in your yard or home do not feed on or harm plants – or people. (So try to think of it as MOST insects you encounter in your garden are the “good” bugs.”) Certainly, there are many pest insects such as aphids, scales, various caterpillars and beetles that cause problems for plants. But there are also many beneficial insects that feed on and destroy insect pests.

The following info is a summary of a longer fact sheet from Colorado State University Extension (see Work Cited below).

Some beneficial insects are classified as predators. They actively seek out and eat harmful insects. Lacewings, spiders (arthropods), and ladybugs, also known as ladybird beetles or lady beetles, are predators. Tachinid flies, Braconid, and Ichneumonid wasps are parasitic insects that live in and feed on the eggs or bodies of insect pests.

Lady beetle larva

As many insects develop, they go through a life-cycle process called partial or complete metamorphosis. Most gardeners recognize the adult versions of various insects. The younger, larval stages of these insects look very different. Often it is immature larvae that do the most work fighting insect pests. Gardeners should be able to recognize – and not destroy – the immature stages of these insects. For example, ladybug larvae look nothing like the familiar adult ladybugs that are red with black spots. Ladybug larvae are elongated and dark in color, flecked with yellow or orange markings. Green lacewing larvae are similar in general appearance to ladybug larvae but are light brown with hooked jaws that project forward. These larvae are voracious predators that feed on insect pests. Adult green lacewings (seen on a peony in the topmost photo), pale green insects with large, clear, highly-veined wings, feed on plant nectar.

Green lacewing larva

Syrphid flies, also known as flower flies, are often mistaken for bees or yellow jackets. They feed on flower nectar and are harmless to people. Once again, it is the larval stage of the Syrphid fly that preys on insect pests. These larvae look like small, yellow maggots.

Parasitic Tachinid flies look very much like the common fly. They lay their eggs near the heads of caterpillars and beetles. The eggs hatch and the young tunnel into, feed on, and ultimately kill the host insect. There are many varieties of Tachinid flies that are caterpillar parasites. These flies are rarely observed by gardeners even though they control insect pests.

Many people are terrified of spiders also known as arthropods. But spiders prey on other insects and are often the most important biological control of insect pests in gardens, forests, and fields. Spiders whose bites require medical attention are rare in Colorado. Some spiders actively hunt their prey; others catch prey in webs and use venom to subdue the insect. Recognizing specific spiders can help people avoid the rare ones that are harmful and safely ignore the many others that provide pest controls.

Work Cited:See Colorado State University Extension Fact Sheet 5.550 at www.ext.colostate.edu/pubs/Insect/05550.html

Next week – should you buy beneficial bugs for your garden?

Contributed by Deb Ross, Certified Colorado Gardener
Photo of lacewing on peony courtesy of Carey Harrington.
All other photos courtesy of Colorado State University Extension