Twin spot longhorn beetle (Oberea oculata)
|Also known as:||Eyed longhorn beetle|
|Size||Length: 15-21 mm (1)|
Classified as Endangered in Great Britain (2).
This large and attractive beetle is endangered in the UK (2). It has a long, thin body, and like all members of the longhorn family, has long antennae. In males, these antennae are longer than the body, but in females they are as long as the hard wing cases (elytra) (1). The head and antennae are black, the wing cases are mottled greyish-black, and the abdomen, legs and thorax are orange. Both the common and Latin names refer to the two black spots on the thorax; oculata means 'eyed' (4).
Historically recorded from Kent, Oxfordshire and Cumbria, and during the 19th century was common in East Anglia. After 1890 it was recorded only from around Wicken Fen National Nature Reserve, Cambridgeshire (3). At present just one population is known in Britain, on the Cam Washes, but the location is a closely-guarded secret in order to protect the species from collectors (3). This beetle also occurs in central Europe where it is more common in mountainous areas and is rare further north (1).
This beetle is a species of fen and carr habitats. The remaining colony occurs on purple willows growing in wet conditions next to a body of open water (3). A preference is shown for shoots of the larval host plant that are shorter than 2 meters (3).
Adult females lay their eggs in the straight stems of young purple willows (Salix purpurea). After hatching, the larvae overwinter, and only begin to feed in the following summer. They then live inside the stems, where they take three or four years to develop, and are thought to be inactive from September to April (3). More than one egg is often laid in a single stem, and just 20% of the eggs laid go on to become adults (2).
Although the reasons for the decline are not known, a number of suggestions have been put forward. These include: grazing of the breeding habitat by cattle; the cessation of large-scale sedge cutting and resulting scrub encroachment; reduction in pollarding; increase in woodpecker predation, and the lowering of the water table due to water abstraction and drainage (3).
This beetle is a priority species under the UK Biodiversity Action Plan. The Species Action Plan produced aims to reintroduce the species to at least two former sites by 2005 (2); however the surviving colony of this endangered beetle is too small to be used as a source of reintroductions, and must therefore be enhanced (3). Habitat management, planting of purple willow and surveying is currently underway (3). A Species Action Plan has been produced by the National Trust, which is the lead partner for the conservation of this species.
For more information on this species, see:
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- Abdomen: in arthropods (crustaceans, insects and arachnids) the abdomen is the hind region of the body, which is usually segmented to a degree. In crustacea (e.g. crabs) the limbs attach to the abdomen; in insects the limbs are attached to the thorax (the part of the body nearest to the head) and not the abdomen. In vertebrates the abdomen is the part of the body that contains the internal organs (except the heart and lungs).
- Antennae: pair of sensory structures on the head of invertebrates.
- Carr: term used to describe wet habitats. In East Anglia it is used to refer to wet woodlands, especially alder woods.
- Elytra: in beetles and earwigs, the hard fore wings. They are held aloft when the insect flies, and are often coloured or patterned.
- Fen: wet peat, usually with alkaline water. The alkalinity arises due to ground water seeping through calcareous rocks (rocks containing free calcium carbonate).
- Larval: of the stage in an animal's lifecycle after it hatches from the egg. Larvae are typically very different in appearance to adults; they are able to feed and move around but usually are unable to reproduce.
- Thorax: part of the body located near the head in animals. In insects, the three segments between the head and the abdomen, each of which has a pair of legs.
National Biodiversity Network Species Dictionary (September 2002)
- Harde, K.W. (2000) A field guide in colour to beetles. Silverdale Books, Leicester.
UKBAP Species Action Plan (May 2002):
Latin Dictionary and Grammar aid (May 2002):
Colston, A. & Stebbings, P. (2000). Species Action Plan for the twin-spot longhorn beetle, Oberea oculata. (May 2002):