Selatosomus aeneus (Linnaeus, 1758)
POLYPHAGA Emery, 1886
ELATEROIDEA Leach, 1815
DENTICOLLINAE Stein & Weise, 1877
CTENICERINI Fleutiaux, 1936
Selatosomus Stephens, 1830
This transpalaearctic species occurs from continuously from the west of Europe to the far east of Russia but is absent from Japan, and over much of its north-western continental range is a pest of various crops and young orchard trees. In the U.K. it is locally common throughout England and Wales with the exception of the southeast, and there are a few scattered records from the Scottish Highlands. It occurs in a wide range of woodland, grassland and agricultural habitats where the adults are active from early spring until mid-summer. European populations are more typical of grassland habitats whereas those further east occur in more forested habitats, in the U.K it is a mostly grassland species which has not become a crop pest. Adults occur under debris or among leaf-litter early in the year, becoming active and dispersing by flight during May and June when they feed upon leaves of grass and shrubs for a while before mating, usually on the soil surface in sparsely vegetated areas. Females are very fecund, producing between 300 and 650 eggs which are laid on emerging grass leaves, among leaf-litter or in cracks in the soil. The eggs develop slowly with larvae emerging after four or five weeks, the young larvae move among the soil or litter seeking out conditions of optimal temperature and humidity before they begin to feed upon roots and young shoots etc. and they are also known to consume small insects and larvae, as they grow they move between plants on the surface or through the soil. Development takes between two and four years, or longer at higher continental latitudes, and winters are spent deeper in the soil, they will moult between eight and twelve times and when fully grown will pupate in a deep subterranean cell from July onwards. The adults eclose from August but remain in the cell until the following spring. In parts of Northern Europe the larvae may be the most numerous of all pest elaterids and they commonly attack cereals, sunflowers, potatoes and various vegetables, consuming seedlings and young roots of developing plants and causing deterioration of tuber and root crops. Control measures include deep ploughing etc. but the beetles typically maintain healthy populations in marginal habitats among native grasses and so are very difficult to eradicate in the long term.
Adults are among the more splendid-looking of our U.K. elaterids; 10-15mm long and strongly metallic green, blue or bronze-black with dark antennae and dark to variously red legs. Head densely punctured, with moderately convex eyes and large, curved mandibles. Antennae 11-segmented, segment two as long as segment four and segment four 1.5-2X longer than wide, segments 5-10 expanded towards the apex and rounded, without a distinct angle, the terminal segment widely truncate. Pronotum convex anteriorly, finely and quite densely punctured, more densely so laterally, the anterior margin narrower than the distance between the produced hind angles, and with a sharp but often weakly developed keel parallel to the basal lateral margin. In lateral view the prosternal process is not constricted towards the apex. Elytra widest behind the middle and smoothly curved to acute apices, weakly explanate and with well-impressed and punctured striae, the interstices very finely punctured and glabrous or with sparse and very fine recumbent pubescence. Striae 4 and 4 united and deeply impressed below convex shoulders, all striae complete almost to the apex. Legs generally dark but, especially in continental specimens, with the femora and tibiae variously red. Claws smooth. The eggs are tiny <1.0mm spherical and white, the fully grown larva measures about 25mm and is bright yellow with a metallic reflection and has two incurved and sharply-pointed urogomphi and the pupa is about 16mm in length and lacks pigment.