Understanding and encouraging ground beetles (a natural enemy of crop pests)

There are 350 species of ground beetles (Family: Carabidae) in the UK, of which 20–30 are important for biocontrol.

Eggs are ovoid and usually laid singly in or under the soil.

Larvae are elongated, with biting mouthparts. They have three pairs of legs, each of which has six segments with two claws at the end, and 10 abdominal segments. They can be confused with rove beetle larvae, but the heads of ground beetle larvae are flatter.

Adult ground beetles are of variable size (2–25 mm), are typically black or brown, often with metallic sheens; some are brightly coloured. They have biting mouthparts and are normally seen running on the ground. Most are flightless and usually nocturnal.

Within the ground beetles, there are varying life cycles. For example, some breed in the summer/ autumn and overwinter as larvae, whereas others breed in the spring and overwinter as adults. Others flex breeding times according to the weather, while some have prolonged resting periods as adults. The life cycle can last from one to several years, with between two and five larval stages. Larvae are carnivorous, except for Harpalini spp., which feed upon seeds. Adults usually overwinter outside of the crop, in field margins or woodland, whereas larvae are also found overwintering within fields at densities of up to 1 million per hectare.

Approximately 20–30 species are important for biocontrol; 5–10 are abundant on farmland. Beetles overwintering outside of the crop reinvade in the spring to help control pests, but most remain within 60 m of the edge. Consequently, coverage of large fields may not be achieved.

Ground beetles are generalist predators. They provide a background level of control for a variety of pests, such as aphids, fly eggs and larvae, moth/butterfly eggs and larvae, slugs and weed seeds. They also act synergistically with other natural enemies; for example, consuming pests dropping from the crop as they try to escape other predators or parasitoids.

Learn about the integrated control of slugs

Although abundant on farmland, numbers have recently declined. Ground beetles are killed by most foliar-applied insecticides, as well as intensive soil tillage.

Techniques to encourage ground beetles include:

• Dividing large fields (>15 ha) with beetle banks to ensure more even coverage
• Having field margins with tussock-forming grasses
• Reducing the intensity of soil cultivations
• Using spray thresholds to reduce insecticide applications
• Allowing uncompetitive weeds to survive within the crop: low levels of weeds within crops also help to support ground beetles by providing cover and alternative food (insects and seeds)