Limnoxenus niger (Gmelin, 1790)
POLYPHAGA Emery, 1886
HYDROPHILOIDEA Latreille, 1802
HYDROPHILINAE Latreille, 1802
Limnoxenus Motschulsky, 1853
This Western Palaearctic species is widespread across central and southern Europe from Portugal to Greece and north to the UK and the southern Baltic countries, it is also present on the larger Mediterranean islands, there are records from Turkey, Lebanon and Syria, and as far east as the Caspian sea. The first record from Algeria was recently confirmed (Incekara & Bouzid, 2007), the species having previously been thought to L. olmoi Hernando & Fresneda, 1994, a very local species of Portugal, Spain and North Africa, and the only other European member of the genus. L. niger is generally very local and scarce across Europe, and in some areas there are only very few modern records, in central regions mostly from lowland valleys. In the UK it is most frequent in coastal areas from Essex to Sussex, and from the Somerset Levels, but there are also scattered records from East Anglia and the east midlands, South Wales, and coastal Hampshire and Dorset, including IOW. Habitats include both fresh and brackish water, usually stagnant and densely vegetated pools and drainage ditches, and marshes. Adults have been recorded year-round; they are active over a long season from March or April and peak in abundance during spring and late summer. Dispersal by flight occurs in the spring. Breeding occurs in the spring, and females attach egg cases to vegetation just below the water surface; these were described by Van Berge Henegouwen (1975, available online), and are very distinctive; about 70 mm in length with about 20 mm rising protruding above the water. Larvae develop through the spring and pupation probably occurs among marginal substrate, new generation adults occur in the summer. Typical of the group, larvae are thought to be predacious, and adults probably feed on decaying vegetation although they may also be partly predaceous, but little is known of the biology.
Limnoxenus niger 1
Limnoxenus niger 2
8.0-9.8 mm. Elongate and continuous in outline, dorsal surface finely and densely punctured, glabrous, shiny and convex, ventral surface densely pubescent and flat. Body black, appendages dark brown to black. Head transverse, smooth and weakly convex between large eyes that follow the outline, temples strongly converging, cheeks converging to a smoothly curved clypeal margin. Maxillary palps slender and as long as, or slightly longer than the antennae, the apical segment distinctly longer than the previous segment. Antennae 9-segmented, with a long 3-segmented club. Pronotum transverse, broadest across perpendicular posterior angles and narrowed to a curved apical margin, basal margin simple and almost straight. Prosternum and mesosternum keeled. Scutellum large, triangular, and sculptured as the adjacent pronotal surface. Elytra smoothly curved from rounded shoulders to a continuous apical margin, sutural stria deepened towards the apex, striae otherwise represented by nine regular rows of tiny punctures. Tibiae slender and hardly broadened from the base, each with paired apical spurs. Tarsi 5-4-4, all segments simple. Very similar to Hydrobius, but larger, lacking impressed elytral striae and with keeled prosternum.