Not all critters crawling around garden plants and squirming through the soil are harmful. Some insects and worms have beneficial roles in gardens. You should recognize these helpers to ensure you don't mistakenly kill them. Convergent lady beetles, commonly called ladybugs (Hippodamia convergens), are desirable insects, and species of nematodes, such as roundworms (Steinernema and Heterorhabditis spp.) and earthworms (Eisenia foetida and Lumbricus rubellis), provide benefits to garden soil.
Ladybugs and some worms help reduce populations of predatory insects that can damage or destroy garden plants. This natural elimination of insect pests decreases your need for chemical pesticides. As a result, fewer toxins that may harm fish, plants or warm-blooded animals are released into the environment. Beneficial nematodes are barely visible -- less than 1/5 inch long -- but they can help to curb infestations of destructive insects. Ladybugs provide pest management even as larvae, with immature beetles preying on harmful garden insects. Although not involved in insect control, earthworms improve soil quality and provide essential nutrients to garden plants.
Certain species of roundworms can be as effective as traditional pesticides at controlling certain predatory insects. These nematodes feed on larvae and grubs of insects known to attack garden plants, including rootworms, stem borers, root weevils and cutworms, as well as other backyard pests, like fire ants, flies and fleas. Members of the Heterorhabditis genus of roundworms are particularly effective at combating Japanese beetle infestations. Ladybugs are most useful at controlling soft-bodied, sucking insects, such as aphids and whiteflies, as well as thrips, mealybugs and spider mites. Ladybugs are big eaters, consuming up to 50 aphids a day and as many as 5,000 in their lifetime.
Earthworms and Soil
While roundworms and ladybugs work to control insect pests, earthworms do double duty to improve garden soil. First, earthworms work much like plows as they push and eat their way through soil. As earthworms burrow through the soil, they loosen it, which improves drainage, air circulation and plant root growth. Then, the feeding byproducts pass through earthworms. The dark excreted granular matter is called a worm casting. Worms produce a lot of castings – their weight's worth every day. These castings are rich in essential nutrients required for healthy plant growth and development, and make an excellent garden fertilizer.
Building Beneficial Populations
With such natural benefits, you can do a few things to keep the populations of these critters high. Avoid adding nitrogen-rich synthetic fertilizers to garden soil. Earthworms dislike the resulting increase in soil salinity and will move away. Increase nematode numbers by using a commercial spray, granules or sponges. These products contain hundreds of millions of nematodes and are effective immediately. To attract and retain ladybugs, plant a mix of nectar- and pollen-producing flowering plants. Annual cornflower (Centaurea cyanus) and golden Marguerite (Anthemis tinctoria), which is perennial in U.S. Department of Agriculture plant hardiness zones 3 through 7, are two varieties especially attractive to ladybugs.
- National Gardening Association: Beneficial Nematodes
- CalRecycle: Vermicomposting: Composting With Worms
- University of California Statewide Integrated Pest Management Program: Convergent Lady Beetle
- Organic Gardening: Understanding Earthworms
- The Baltimore Sun: Beneficial Bugs
- Organic Gardening: Flowers for Borders
- Los Angeles Times: Ladybugs Are Good, but Lacewings and Mantises May Be Better
- Washington State University Clark County Extension: The Beneficial Ladybug
- Photo Credit Hemera Technologies/AbleStock.com/Getty Images