Enochrus melanocephalus (Olivier, 1792)
POLYPHAGA Emery, 1886
HYDROPHILOIDEA Latreille, 1802
HYDROPHILINAE Latreille, 1802
Enochrus Thomson, C.G., 1859
For long considered confined to the Western Palaearctic region, but recently discovered in China (Fenlong & Renchao, 2015), this species is widespread in Europe from Portugal to the Balkans, and north to the UK and the Baltic countries where it extends into Southern Norway and Central Sweden. It is also recorded from many of the Mediterranean islands, parts of North Africa, Turkey, Israel, and extends east into European Russia. The species is generally sporadic and very local, occurring from lowlands to Alpine areas where it is very local and rare. In the UK it is widespread though local across Central and Eastern England, but otherwise much more local and scarce throughout England as far north as Cumbria and across Wales. In Scotland it is known only from Kirkcudbrightshire, and most of the few Irish records are from southern and eastern coastal sties. Typical habitats are slow-moving canals and ditches, ponds and lake margins, often sparsely vegetated and exposed to the sun, and often on calcareous substrates although it has also been recorded from brackish pools in coastal areas. Adults are present year-round, they are active from March until October and they peak in abundance during May. Dispersal occurs by flight in the spring, and at this time adults are attracted to light. Breeding also begins in the spring but details are unknown; typical of the genus females produce a silken egg case which is probably attached to aquatic vegetation so that a ‘mast’ protrudes so allowing gaseous exchange, larvae are aquatic but development varies widely in the genus, from a few weeks to two months, and pupation probably occurs out of water among marginal substrate. Larvae are predaceous whereas adults feed on algae and decaying vegetation. Following a peak during May the adults remain common through the summer and there are no further peaks later in the year, suggesting the species is univoltine. Head black with a pale mark in front of the eyes, pronotum pale brown with four small dark marks forming a square, elytra pale brown, maxillary palps pale with the terminal segment darkened apically, antennae pale with darker clubs, legs dark brown to black. Head slightly uneven between large and slightly-protruding eyes, surface more finely and less densely punctured than the pronotum.
Enochrus melanocephalus 1
4.2-5.5 mm Elongate-oval and continuous in outline, dorsal surface glabrous and convex, ventral surface black, finely pubescent and flat. Maxillary palpi much longer than the antennae, penultimate (third) and terminal segments about equal in length, this feature is diagnostic among our European species; in all others the terminal segment is distinctly shorter than the third segment. Antennae 9-segmented with a loose 3-segmented club. Pronotum transverse, broadest across perpendicular posterior angles and narrowed to slightly projecting anterior angles, apical margin curved, basal margin very finely bordered and almost straight. Pronotal surface smoothly convex, without depressions or structure, and finely and densely punctured throughout. Scutellum elongate and triangular, punctured as the adjacent pronotum. Elytra smoothly curved and narrowed from rounded shoulders to a continuous apical margin, sutural stria deepened beyond the basal quarter or so, otherwise with weakly impressed longitudinal lines although these may be very faint or hardly visible. Elytral punctation fine and dense, similar to that on the pronotum. Tibiae slender, with well-developed apical spurs. Tarsi with five simple segments. Front claws strongly curved in males.