Odacantha melanura (Linnaeus, 1767)
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ADEPHAGA Clairville, 1806
ODACANTHINI Laporte, 1834
Odacantha Paykull, 1798
The tribe Odacanthini Laporte, 1834 is variously classified as a group within Lebiinae or Harpalinae or considered sufficiently distinct to warrant its own subfamily, Odacanthinae. The group is very diverse in warmer regions but only very poorly represented in temperate areas e.g. of the 33 genera only 2 are represented in Europe, each by a single species, and 5 species of a single genus occur in North America , by contrast 50 species representing 16 genera occur in Australia. Of the European species Eucolliuris olivieri (Buquet, 1864) is restricted to Southern Spain, North Africa and the Balearic Islands while O. melanura occurs throughout Europe except for many Mediterranean areas, extending north into the southern provinces of Sweden and the UK and east into Siberia. In the UK Odacantha melanura is a very local and generally rare species; it is almost entirely confined to South Wales, southern England and East Anglia, many records are coastal and it is virtually absent from The West Country and the English midlands. Adults are generally associated with well-vegetated margins of reedbeds and floating reed rafts and are present year-round; they overwinter in stems of rushes (Typha L.) and reeds (Phragmites Adans.) etc. and become active in March or April; they are diurnal and predatory, spending much of their time climbing stems in search of springtails and aphids, and almost always occur among reeds but may also be found among patches of sweet grass (Glyceria R.Br.) and other marginal vegetation, usually in small numbers and often in company with other reedbed carabids such as Agonum thoreyi Dejean, 1828 and Demetrias imperialis (Germar, 1823). Reproduction occurs in the spring and larvae develop within hollow stems of reeds and rushes, new-generation adults occur from late summer and so adults may be present continuously, the previous generation usually persisting into July or August. Flight ability is unknown; in Central Europe adults are macropterous but in the north they have reduced wings and dispersion is thought to occur by climbing among stems.
Easily recognized by the distinctive colouration and habitus; forebody, elytral apex and abdomen shiny black with a metallic green or blue reflection, base of elytra, meso- and metasternum pale brown to reddish-brown, antennae dark with three basal segments pale, legs pale with femoral apices and tarsi darkened. Head smooth and shiny; broader than the pronotum and evenly convex, with long and curved temples and a short neck, inner margin of eyes with 2 setiferous punctures. Prothorax elongate and cylindrical, lateral margins curved and constricted before weakly protruding posterior angles, dorsal surface finely to moderately strongly punctured and (usually) strongly transversely wrinkled. Elytra elongate and flattened, with sloping shoulders and sinuate and separately curved apical margins, striae present as rows of fine punctures which may lie in weak longitudinal impressions, especially towards the apices. Tarsi without bilobed segments, claws smooth, basal segments of front tarsi weakly dilated.
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Our single species is very distinctive and typical of much of the group but exotic genera display a wide range of morphology e.g. the head and prothorax vary from quadrate and rounded to cylindrical and very elongate, the pronotum from cylindrical to flattened and strongly bordered, the elytra smooth to strongly punctured and deeply striate and the fourth tarsomere may be simple or strongly bilobed, and while some species are drab black or dark brown, the majority are strongly coloured and/or patterned.