Twin Spot Longhorn Beetle

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).

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.

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).

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).

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).

Classified as Endangered in Great Britain (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).

Foodplant / internal feeder
larva of Oberea oculata feeds within live pith (young stem) of Salix

Oberea oculata is a species of beetle in the family Cerambycidae. It was described by Carl Linnaeus in 1758, originally under the genus Cerambyx. It has a wide distribution throughout Europe. It feeds on Salix alba, Salix acutifolia, Salix pentandra, Salix caprea, and Salix triandra, and serves as a host for the parasitic wasp Ephialtes manifestator.

O. oculata measures between 15 and 21 mm (0.59 and 0.83 in).