The busy ground beetles' diet can help control slugs, asparagus beetles, caterpillars, Colorado potato beetles, corn earworms, cutworms, squash vine borers and tobacco budworms.
Illustration By Keith Ward
This article is part of our Organic Pest Control Series, which includes articles on attracting beneficial insects, controlling specific garden pests, and using organic pesticides.
Ground Beetles (Coleoptera)
Most of the 2,500 ground beetle species are one-eighth to 1 1/2 inches long, dark, shiny and hard-shelled. Shape and color varies among species, with most being brown to black while others have metallic backs. Ground beetles live in the soil beneath mulches, around compost piles, or in the sheltered areas around perennials plants. Some of these beneficial garden insects create vertical tunnels that they use to ambush and trap prey, but most ground beetles wander about feeding at night. Compared with other garden insects, ground beetles are long-lived and may inhabit the garden for more than a year, overwintering as adults.
Ground Beetle Diet
Ground beetles will try to eat almost anything that moves, including asparagus beetles, cabbage worms, Colorado potato beetles, corn earworms, cutworms and slugs. Some are also important consumers of weed seeds. Ground beetles also eat earthworms, but their benefits outweigh this small flaw. Ground beetles cannot climb, so their foraging range is limited to the soil’s surface and top few inches of moist soil.
How to Attract Ground Beetles
Maintain stable habitats for ground beetles consisting of nicely mulched perennial plants that are customarily watered in dry weather. Flat stones or boards also serve ground beetles by providing safe places to rest during the day. Grow clovers in pathways. Bushy amaranth plants also are attractive to ground beetles. Do not use pesticides in the garden, as ground beetles are highly sensitive to anything but Bt. (Bacillus thuringiensis). Ground beetles can be collected from rotting logs or the wood pile and released in the garden.
More information about these helpful garden insects is available from Washington State University, University of Minnesota, and Cornell University.