Ground beetles
Ground beetles are the fast, shiny, usually black beetles that run when you lift a stone or a pot. They are predators, not pests: adults hunt at night on the soil surface, and the larvae hunt in the litter and topsoil, eating slugs and snails, caterpillars such as cutworms, root maggots and other soft-bodied soil insects. Some species also eat large numbers of weed seeds. North America has more than 2,200 species. You cannot buy them. You keep them by leaving cover such as mulch, stones and leaf litter, and by not treating the soil with broadcast insecticides.
At a glance
- Kind
- Wild — attracted, not bought
- Adult
- 1/8–1 in (4–25 mm); shiny, long legs
- Active
- At night; hides under objects by day
- Eats
- Slugs, caterpillars, root maggots, soil insects
- Life cycle
- Often one generation a year; adults can live 2+ years
- Species
- More than 2,200 in North America
How it works
Adults are elongate, usually shiny black or dark reddish, and some are brilliantly coloured or iridescent. They have long legs, threadlike antennae, prominent jaws, ridged wing covers and a head narrower than the thorax behind it. They rarely fly. By day they hide under stones, boards, pots, mulch, leaf litter and compost, especially where it is damp, and at night they run over the soil hunting. The larvae are elongate, with a relatively large head and curved, forward-pointing jaws, and live in the litter and topsoil, where they eat soil-dwelling insects.
Prey includes caterpillars, root maggots, slugs and snails, millipedes and other ground-level invertebrates, and different species specialise. Large species such as Carabus and Pterostichus melanarius are known slug hunters, and the fiery searcher, a brilliantly coloured caterpillar hunter, was imported to attack spongy moth larvae. Others eat seeds: field studies have found ground beetles removing 65–90% of some weed seeds shed each year. They develop slowly. Many take about a year from egg to adult, and adults can live two years or more, so a population builds over seasons in undisturbed ground, not in weeks.
What it is confused with
Ground beetles are easy to mistake for pest beetles because they are dark, fast and turn up in the soil where damage is being done. Three lookalikes are worth knowing.
- PestDarkling beetles — Also dark and similar in build, but they feed on plants. UC IPM notes that ground beetles have enlarged basal leg segments that partly cover the abdomen, and that a darkling beetle's antennae attach beneath a distinct ridge.
- Also goodBombardier beetles — A ground beetle that, when threatened, raises the end of its body and fires a hot chemical gas with a popping sound. It is a predator like the others; do not handle it.
- Also goodRove beetles — Wing covers so short that they leave the abdominal segments exposed from above. Ground beetles lack this; their wing covers are ridged.
How to keep it around
Ground beetles rarely fly and can live for years, so habitat matters more than flowers. Give them somewhere damp and dark to hide by day, and leave the soil undisturbed where you can. In a South Carolina trial, plots mulched with cover-crop residue caught more ground and rove beetles than bare, tilled plots in at least one year. On farms, 'beetle banks' and field margins are kept to give natural enemies shelter and overwintering sites for the same reason.
- Keep a mulch of straw, leaves or cover-crop residue on beds rather than bare soil
- Leave stones, boards, logs or upturned pots at bed edges as daytime shelter
- Keep a permanent strip of grass, perennials or leaf litter beside the vegetable beds
- Keep a compost heap; ground beetles hide and hunt in it
- Dig and till only as much as you need to
- Avoid broadcast soil insecticides, which kill soil-dwelling beetles along with the pest
Pesticide sensitivity
UMass warns that soil-dwelling beetles are susceptible to insecticides, so broadcast soil treatments should be avoided. In Mid-Atlantic corn and soybean fields, however, neonicotinoid seed treatments and foliar sprays had no significant effect on ground beetle activity in a two-year survey of 37 fields. Open the compatibility matrix →
When to choose something else
Ground beetles are the background check on ground-level pests. They are not a fix you can call on. Look elsewhere when:
- Slugs are shredding lettuce or hostas now — beetles catch slugs on the soil, not up in the plant; see the slug page for traps, barriers and baits
- Damage is below ground, on seedlings — slugs that stay in the soil are out of the beetles' reach
- You need a control you can buy for cutworms — the nematode Steinernema carpocapsae is sold for them
- The pest is up in the canopy, such as hornworms or aphids — most ground beetles hunt at soil level
Ground beetles by target
What it eats and when it turns up differ by pest. Each page below is the picture for one target.