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Bug of the Month: European ground beetle

Common name: European ground beetle

Latin name: Carabus nemoralis

Taxonomy:
Kingdom Animalia
   Phylum Arthropoda
      Class Insecta
         Order Coleoptera
            Family Carabidae

 

Head of European ground beetle
Ground beetles in general

Ground beetles (Family Carabidae) are an extremely diverse, abundant, and widely-distributed group of beetles. Most species in this family are agile hunters and make their living eating other invertebrates; a few species are seed eaters. Both eating habits have made carabid beetles important to humans as natural control agents for invertebrate pests (including gypsy moth caterpillars) and weeds. As their name suggests, most ground beetles live at the ground surface, either in the soil or leaf litter, but others are found under bark or up higher in the vegetation. Species within the family vary greatly in their sensitivity to environmental conditions (e.g., some species occur across a wide range of habitats, others may be restricted to stream edges or dry meadows etc.) and also in their ability to disperse (some species are good fliers, others don't fly at all).

Because of the diversity of habits among species and the relative ease with which the beetles can be sampled (with "pitfall traps"), ground beetles have been relatively well-studied and much is known both about their taxonomy and natural history. As a result, ground beetles have often been used as subjects in ecological and biodiversity studies. One such study on the Boston Harbor Islands has related the flight capability of different ground beetle species to their distribution across islands at different distances from the mainland—testing the theory of "island biogeography." There are more than 2200 species of ground beetles in North America, and we have documented over 120 species on the Boston Harbor Islands (more than any other single beetle family).

Overhead view of European ground beetle, showing its purple and coppery colorsHow to identify European ground beetles

Most species of ground beetles found on the Boston Harbor Islands are dull brown or black in color, with long parallel grooves and ridges on the "back" of their abdomen (which is actually the hardened front pair of wings, or "elytra"). They have long legs which allow them to move quickly along the ground in search of prey. European ground beetles are easily distinguished because they are the largest ground beetles on the islands (about an inch long), and their upper thorax and elytra are metallic purple or coppery in color. The elytra each have 3 rows of dimples running along the ridges.

Where to find European ground beetles on the Boston Harbor Islands

Like most ground beetles, European ground beetles are active at night, and during the day they can often be found resting under leaves or other objects on the ground (rocks, boards etc.). This species is often found in habitats associated with humans, such as gardens and near buildings. On the Boston Harbor Islands you are likely to find European ground beetles just about anywhere: in forests, scrubland, open grassy areas, and near buildings. They are often found in large numbers in a single area.

Front, angled view of European ground beetleHow European ground beetles make a living

Adult beetles spend the winter hibernating in the soil or leaf litter, under bark or stones. They mate in the spring, and females lay their eggs in the soil. Egg and larval stages are completed through the spring and summer, and the new adults appear in late summer to early autumn. Individuals may live two years or, rarely, longer. European ground beetles have large mandibles which they use to feed on soft-bodied prey like slugs, earthworms, and caterpillars; the larval beetles are also fierce predators. They are good to have in your garden! Like many ground beetles, this species can emit a very smelly (but otherwise harmless) substance from glands in its abdomen if you pick it up. European ground beetles have non-functional hind wings and cannot fly.

Where in the world European ground beetles occur

This species is native to Europe, from where it was introduced to both coasts of North America. It is most common in the northern U.S. and Canada, and its range is expanding inland. 

To learn more about European ground beetles (and ground beetles in general)

On the web:

In print:

    Larochelle, A. and M.C. Larivière 2003. A Natural History of the Ground-Beetles (Coleoptera: Carabidae) of America north of Mexico. Pensoft Publishers, Bulgaria.

    Lindroth, C.H. 1961 1969. The Ground Beetles (Carabidae, excl. cicindelinae) of Canada and Alaska. Parts 1-6. Opuscula Entomologica Supplementa 20, 24, 29, 33, 34, 35:1-1192.