Bugs are the flying and crawling critters you find in your garden. Scientists divide them into groups.

The largest group is insects, such as butterflies, bees and beetles, which have three pairs of jointed legs and two pairs of wings. Other groups include spiders (arachnids), sowbugs (crustaceans), snails (mollusks) and worms (annelids). While some bugs damage our plants, many beneficial ones protect our gardens by eating the bad bugs.

Lady beetles are the most widely known predatory insect, both in its adult and larva forms. They form a pest patrol, feeding on plant-eating insects such as aphids. Aphids suck the juice out of our plants and secrete sweet honeydew that attracts ants. The larva of another insect, the green lacewing — sometimes called “aphid lion” — is a voracious predator capable of eating up to 60 aphids an hour. Adult lacewings feed on flower nec

tar and help to pollinate our plants.

Another important garden ally is the nematode, a microscopic parasitic worm that acts as a biological control for many troublesome garden pests. These non-segmented roundworms are too small to be seen with the naked eye, but they are a powerful pest management tool. They help control pests like slugs, ants and beetles that would otherwise devastate your garden. They provide a way to avoid the use of artificial chemicals, such as pesticides. Note: These are not the same as root-knot nematodes, which are plant parasites that damage the roots of specific plants.

There are more than 20,000 known species of beneficial nematodes. To use them effectively, you must first identify the pest bothering your garden and then choose the corresponding nematode that targets it. You can purchase nematodes online or from your local garden center. Keep them refrigerated until you’re ready to use them.

To apply, mix the nematodes with water and apply using a watering can, hose-end sprayer or pump sprayer. Check the product label for the correct application rates. Quantities can range from the millions to the billions. For example, 5 million nematodes typically treat approximately 1,600 square feet.

A common lawn pest is the masked chafer. Its larvae — white C-shaped grubs — feed on grass roots, causing significant lawn damage and dead patches of grass. Even worse, raccoons come to feed on the grubs, tearing up large sections of grass in search of a meal. When beneficial nematodes are applied, they find the grubs and attack, releasing bacteria that kill the pests within 24 to 48 hours. The nematodes then use the grub body as a breeding ground, increasing their population and sustaining pest control.

The best time to apply nematodes is late summer or early fall when the soil temperature is above 60 degrees. Water the lawn before application to ensure the nematodes move through the soil effectively. Apply in the morning or evening for the best results. Keep the soil moist after application to allow the nematodes to establish. Two applications two weeks apart offer complete coverage.

Beyond grubs, nematodes can be effective in controlling fleas, cutworms, root weevils, mole crickets, codling moth larvae, thrips, armyworms and fungus gnats. Each one has specific nematodes that can target these pests.

• Steinernema carpocapsae targets cutworms, billbugs, crane flies and lawn moths.

• Steinernema glaseri and Heterorhabditis bacteriophora target white grubs.

• Steinernema feltiae targets thrips.

The use of nematodes is safe for people, pets and plants. Since nematodes are naturally occurring organisms, they do not leave harmful residue in the soil or groundwater.

Remember that certain plants attract and support our garden helpers so they stick around and do their important job of controlling the bad bugs. Good bugs pollinate our food crops, enrich and fertilize the soil, eat our garbage and provide food for wildlife. Some give us honey, wax and silk. The bugs that are food for other animals and regulate the pest populations are our allies in maintaining the web of life in a healthy, Earth-friendly garden.

Sponsored by UC Cooperative Extension, the University of California Marin Master Gardeners provides science- and research-based information for Marin home gardeners. Email questions to helpdesk@marinmg.org. Attach photos for inquiries about plant pests or diseases. Please call 415-473-4910 to see when a master gardener will be at the office or drop off samples 24/7 in the sample box outside the office. To attend a gardening workshop or subscribe to Leaflet, a free quarterly e-newsletter, go to marinmg.ucanr.edu.