Carabus violaceus


Carabus violaceus, sometimes called the violet ground beetle, or the rain beetle is a nocturnal species of a beetle, from the family Carabidae.

Classification

Carabus violaceus was named by Carl Linnaeus, in the 10th edition of [Systema Naturae|10th edition of Systema Naturæ]. The description of C. violaceus was published in the work's first volume, in 1758. Linnaeus gave its habitat as European forests, and described it as a winged beetle with black wing cases with metallic margins and a somewhat purple thorax. Carabus violaceus is classified in the Megodontus subgenus, and is considered a "species complex with numerous forms that display slight morphological differences".
Three subspecies of the Carabus violaceus exist. Besides the nominate subspecies C. violaceus violaceus there is also C. v. purpurascens, which has been subject to some systematic controversy: for the past 80 years or so, some taxonomists have ranked it as a species on its own – Carabus purpurascens – while others still considered it a subspecies. However, recent analyses using morphometrics and genetics have "justified" treating the taxon as a subspecies of Carabus violaceus. The two subspecies are known to hybridize. A third subspecies, C. v. picenus is the sister taxon to C. v. violaceus, and is a "conglomeration" of well-known populations. The average genetic divergence between subspecies at the same gene is "comparably high".

Description

Violet ground beetles are flightless beetles, with a black head, thorax and abdomen black with purple lateral margins, and black underside, antennae, and legs. The antennae measure half the length of the body; the thorax is nearly heart-shaped, scalloped at the front and bordered at the back; the elytra are joined, smooth and without ridges or indentations, but do have tiny bumps arranged in "indistinct lines". The body is usually between long. The species appears similar to Carabus problematicus, but the colour on C. violaceus' pronotum is more extensive.

Distribution

The species is distributed across the Euro-Siberian region. It is common throughout Great Britain.

Ecology

Violet ground beetles live in woodlands both ancient and recent and some adjacent habitats. Because they are flightless and restricted to forested habitats, they are vulnerable to habitat fragmentation and have low dispersal ability: one study showed that only a few kilometres of grassland were enough to render the beetles unable to settle in forests on the other side. However, the subspecies C. violaceus picens is known to inhabit high-altitude pastures. Stomach content examinations have meanwhile shown that jackdaws sometimes feed their nestlings violet ground beetles, among other insects, and that blackbirds also sometimes eat the beetles.