Haliplus lineatocollis (Marsham, 1802)
Of the 8 species of the subgenus Neohaliplus Netolitzky, 1911 only 2 are known from Europe; H. ruficeps Chevrolat, 1861 has been recorded from Greece and Sardinia while the present species is a very widespread Palaearctic native occurring throughout Europe from North Africa to Southern Scandinavia and east through The Middle East, Asia Minor and Western Russia. Throughout most of its range H. lineatocollis occurs from lowland to low-mountain altitudes up to 2200m. Here it is common across the UK north to Orkney and Shetland and is eurytopic, occurring in most wetland situations in both still and slow-moving water, especially where there is abundant aquatic vegetation. Adults occur year-round; through the winter among substrate under accumulated organic debris, under stones or beneath the bark of submerged logs etc. and active among marginal vegetation at other times. Mating occurs in the spring and oviposition proceeds through the spring and summer, eggs are laid in the stems of aquatic plants and larvae emerge soon afterward. In warmer parts of Europe new-generation adults appear late in the summer but at higher latitudes larvae overwinter out of the water and pupate in a chamber at the water’s edge in the spring to produce new-generation adults early in the year. Larvae feed on filamentous algae while adults predate small larvae etc. and may also consume algae. Sampling adults is straightforward, especially so as the species is distinctive enough (look for the dark line on the pronotum) to be recognized in the field, sweeping among aquatic vegetation or searching debris or floating logs will often produce them in numbers, and in the spring they occasionally occur at light.
2.6-3.5mm, dark testaceous with the head, a median line on the pronotum, and various elytral markings darker. Dorsal surface glabrous and without sensory setae. Head smooth and shiny, finely and densely punctured and with convex eyes occupying most of the lateral margin. Pronotum broadest across the base and strongly narrowed to weakly protruding anterior angles, basal margin strongly sinuate and produced medially. Lateral margins distinctly bordered. Surface densely and finely punctured apically, more sparsely so towards the base, with a long arcuate impression either side of the middle; from the basal margin to about half the length- a feature unique among our species, a few others have a basal impression but in all cases it is much shorter, extending no more than a third of the pronotal length. Scutellum hidden under the pronotal margin. Elytra rather parallel-sided, with strongly punctured striae complete to the apex, and very finely punctured and flat interstices, some of which are carinate close to the basal margin. Legs pale testaceous; all tibiae with a pair of stiff spines on the inner apical angle. Tarsi 5-5-5 with the terminal segment notably elongate; male with basal pro- and meso-tarsal segments weakly dilated. Claws more-or-less equal on all legs.