Helophorus brevipalpis Bedel, 1881
Generally common and usually abundant throughout Europe from the Mediterranean to the Arctic circle in Scandinavia and east through the Caucasus, Israel, Iran and western Asia; it is generally the most common member of the family and occurs throughout the UK including all the islands north to Orkney and Shetland. A single record, including only females, from Utah represents the only confirmed occurrence in the United States; in Spain some spring-dispersing females have been found to be the result of parthenogenetic reproduction. Adults occur year-round in most wetland situations including brackish water pools and salt marshes, and may occasionally be found on the seashore under seaweed; they typically prefer stagnant and well-vegetated, still or slow-moving water and will frequently be found in temporary pools in woodlands etc. They become active early in the year and are soon abundant among marginal vegetation etc., at this time they are sexually mature and will have mated the previous season, oviposition begins early in spring when a proportion of the females will lay eggs local to their overwintering sites but most will disperse by evening or night-time flight to find new habitats, these dispersing females have been found to contain larger oocytes and obviously contribute to the species success in colonizing new areas, at this time they will often be found remote from suitable habitats and may occur in numbers at light traps. Eggs are laid in a silken cocoon constructed by the female on marginal silt or among vegetation, in the present species this consists of an egg-chamber with a concave and leaf-like mast which may act as a plastron during temporary flooding. Larvae emerge within a week or so and are terrestrial, living among marginal soil etc. and feeding upon small organisms; they develop rapidly, passing through 3 instars and becoming fully grown within 2 to 3 weeks, they then burrow into soft marginal substrate to pupate and adults eclose within 2 weeks. New generation adults may emerge or remain in the soil for a few weeks but from June or July they become abundant and disperse to new areas in numbers and at this second dispersal they may occur just about anywhere, they are attracted to light and polarized surfaces (i.e. water) and so commonly alight on vehicles etc. Newly
eclosed adults are sexually immature and remain so until October or November when mating begins, depending upon conditions some will remain active and produce eggs through the winter but the majority will overwinter among litter or tussocks etc. near marginal situations and oviposit in the spring. As well as being our most common water beetle this is also relatively straightforward to identify; the elytra lack a scutellary striole, the terminal segment of the maxillary palpi is symmetrical and the lateral margins of the pronotum are evenly and gently curved or only weakly sinuate from the middle to the posterior angles.
2.0-4.1mm very typical of the family and readily identified as above but the general appearance is widely variable as very dark as well as very pale specimens occur, generally the forebody is dark metallic and the elytra sandy-brown with various oblique darker markings, especially an inverted V-shaped mark at the apical third. The granulate pronotal surface is dark with a brilliant red, purple or green lustre and usually contrasting with the bright golden longitudinal grooves. Similar to the mostly western and northern species, H. avernicus Mulsant, 1846, but with distinctly elongate terminal maxillary palpomere, evenly curved pronotal margin and all elytral interstices similarly convex.