Agriotes obscurus (Linnaeus, 1758)

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POLYPHAGA Emery, 1886

ELATEROIDEA Leach, 1815

ELATERIDAE Leach, 1815

ELATERINAE Leach, 1815

AGRIOTINI Laporte, 1840

Agriotes Eschscholtz, 1829

This very common species occurs from lowlands to the alpine zone throughout almost the entire Palaearctic region from Western Europe east to China and Japan; it is abundant across Europe except for the far north and has become established in eastern North America through accidental introductions. Here it is very common across England and Wales and rather less so further north to Orkney, it is present on all the islands and there are a few, mostly coastal, records from Northern Ireland but it seems to be absent from the south. In northern Europe and Asia it is often abundant coniferous forests but in the UK typical habitats are open grassland, wasteland, parks and road verges; they often occur on disturbed land and in gardens and may be very abundant on agricultural land where large populations can be harmful to crops. Adults appear in March or April and are active into the summer, they feed on grasses and emergent vegetation and are mostly nocturnal but they move on to flowers as they begin to bloom and sometimes appear in numbers on hawthorn and umbels. Mating occurs early in the season and pairs will often be seen on flowers, females choose damp and often shaded situations to oviposit and lay groups of eggs directly into the soil; they often choose areas of dense grass and oviposit around tussocks or among mats of couch grass (Elymus repens (L.) Gould) etc., each will lay between 75 and 230 eggs over an extended period and this behaviour often causes problems in arable situations as the larvae are root feeders and widely polyphagous. Larvae emerge after three or four weeks and immediately begin to feed, they readily consume grass roots and are known to predate other larvae but they also attack tubers and root vegetables, they can be very injurious to cereal crops as they consume seeds and destroy small seedlings, among such crops populations of thirty or forty larvae m-2 are common and in serious infestations can reach 180 m. Larval development can extend over four years and involve up to 11 instars, they are active in temperature between 10 and 35°C and soil humidities around 55% and so they move deeper (> 30cm) into the soil during the summer and winter to avoid adverse conditions, at these times they are less destructive but also less prone to the effects of insecticides but deep ploughing is often used to destroy them or bring them to the surface where they are predated by birds and ground beetles etc. Pupation occurs deep in the soil, between 20 and 50 cm, during July and August and adults are fully-formed within a few weeks but they remain in the soil to overwinter and emerge the following spring. Adults are very likely to appear when sweeping or beating foliage or flowers in spring and early summer, they often occur with other common members of the genus but the broad and robust appearance will soon become familiar.

Agriotes obscurus 1

Agriotes obscurus 1

Agriotes obscurus 2

Agriotes obscurus 2

Agriotes obscurus 3

Agriotes obscurus 3

Agriotes obscurus 4

Agriotes obscurus 4

7-10mm.  A broad species with a transverse pronotum; very variable in colour from pale yellowish-brown to very dark brown, dorsal surface with fine creamy pubescence throughout and appendages always pale brown. Head densely punctured and rugose, with weakly convex eyes that usually touch the margin of the pronotum, antennae filiform with all segments elongate, the basal segment shorter than the next two and the second segment very nearly as long as the forth. Pronotum slightly transverse, broadest across the middle and curved laterally to a rounded anterior margin and sinuate margin outside produced posterior angles, basal margin strongly sinuate, surface evenly convex and densely punctured, the punctures separated by at most their diameter, often less. Elytra with sloping shoulders and evenly curved to an acuminate apical margin, with narrow impressed and punctured striae complete to the apex and flat, finely and randomly-punctured interstices. Legs long and slender, all tibiae with fine spines and pubescence throughout and very fine apical spurs. Tarsi 5-segmented; all segments simple and distinct, the forth only slightly shorter than the third. Claws smooth and without a basal tooth.

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Agriotes obscurus 2