Blue ground beetle (Carabus intricatus)

SizeLength: 25 - 38 mm

The blue ground beetle is classified as Near Threatened (NT) on the IUCN Red List (1).

A large and impressive beetle, the blue ground beetle (Carabus intricatus) has an attractive metallic purple or blue sheen to it. It does not possess wings, although it does have 'typical' beetle wing cases. These have a rough surface, described as looking like a 'rugged landscape' under the microscope. It was only recorded three times in the twenty years prior to 1993 and was considered extinct in Britain until a specimen was found in 1994.

The blue ground beetle is found throughout Europe where it is known to be in decline. It is considered a threatened species in the Netherlands, Belgium, Luxembourg and Denmark. In the UK is has always been considered rare, known from only 12 sites in Devon and Cornwall. In 1994, it was found in just two small woodlands, on the edge of Dartmoor but, by 2000, it had also been found at a total of six sites, one near the two Dartmoor sites and three on the edge of Bodmin Moor.

The blue ground beetle is associated with damp, rotten moss-covered wood in mature beech and oak woodland. It seems to prefer little or no ground vegetation, and requires a humid atmosphere and a moist, peaty leaf-litter, with grazing to reduce the build-up of ground vegetation.

Until recently, little was known about the life cycle of the blue ground beetle, but following field research, more is known now about the adults. Blue ground beetles are nocturnal carnivores, and tests have shown they prefer a certain species of slug Limax marginatus. (They were also found to have a taste for liver, dog food and crabsticks!) In the wild, the adults are found under bark on deadwood, and under rocks.

The beetles seem to be active throughout the year and a fully-grown larva has been found in summer. This specimen also ate slugs prior to pupating, and emerged as an adult some three weeks later. It is thought that, being a large beetle, it may take two years to complete its life cycle. The adults are known to be very long-lived by beetle standards.

As much still remains to be discovered about the beetle's full life cycle, the current theory for its decline suggests that loss of appropriate woodland conditions, over-vegetation of the woodland floor and lack of suitable grazing may have contributed to its rarity.

The blue ground beetle is listed in the UK Biodiversity Action Plans (UKBAPs), and has been included in English Nature's Species Recovery Programme (SRP). Dartmoor National Park, English Nature's joint lead partner working on this species, has commissioned a number of annual reports to discover more about this rare beetle, particularly about the larval stage of its life cycle.

Future work aims to choose a number of suitable sites close to existing populations, and it may prove possible to re-introduce beetles to these sites. Captive breeding is being used to discover more about the beetle's larval stage.

Information supplied by English Nature.

  1. IUCN Red List (March, 2011)