HELOPHORIDAE Leach, 1815
Grooved Water Scavenger Beetles
Includes several very common and widespread species, the ubiquitous H. brevipalpis is especially abundant in almost any wetland situation.
POLYPHAGA Emery, 1886
HYDROPHILOIDEA Latreille, 1802
The Helophoridae is a small family of around 200 described species included in several subgenera of the single genus Helophorus Fabricius, 1775. They are a mostly Palaearctic, and to a lesser extent Nearctic, group but a few occur in tropical Africa and Central America and there is a single Indomalayan species. There are about 150 Palaearctic species of which about 100 occur in Europe, whereas about 50 occur in North America of which 27 occur in Canada. Some species e.g. H. arcticus Brown, 1937, the only member of the subgenus Orphelophorus Orchymont, 1927, occur at high latitudes. The U.K. fauna includes 20 species classified among 6 subgenera. The species of Helophorus, while showing variation in detailed external morphology, are a uniform group and instantly recognizable by the (usually) elongate shape and dorsal sculpturation. They are mostly small, 2-9mm, and drab insects ranging from black to almost completely yellow but the majority are some shade of brown with darker markings which often form a pattern characteristic of a species. The head and pronotum are granulate and usually, at least to some extent, metallic. There is a variable Y-shaped impression on the head and the eyes are convex and prominent. The antennae are 8 or 9 segmented with a loose club consisting of 3 segments and a basal cupule; one of the flagella segments is pointed and used to break the water surface when the beetle is replenishing its air-supply, the pubescent antennal club being pulled back under the head to form a connection between the atmospheric air and that in the plastron covering much of the ventral surface and connected to a sub-elytral air supply. The palps are about as long as the antennae with all the segments elongate, the terminal segment being longer than the penultimate. The pronotum is usually transverse and arched, at least to some extent granulate, and has 7 longitudinal furrows on the surface; this feature separates the Helophoridae from other families of the Hydrophiloidea. It is generally broadest anteriorly with prominent front and hind angles and the lateral margins are sinuate. The microsculpture and colour varies although a frequent pattern is dark with at least part of the margin paler. The scutellum is small but easily visible. The elytra are elongate and generally broadened around the middle, smoothly rounded apically and entirely covering the abdomen. The
humeral convexity may be well-developed and there are strongly punctured striae including, in some subgenera, an intercalary stria. In some there is a wide and transverse, V-shaped impression before the middle. The legs are usually long and slender and the tarsi are 5-5-5 although the meso- and meta-tarsi may appear 4-segmentd as the basal segment is tiny. The wings are well-developed and the adults fly readily. Most are wetland species which possess fine and sometimes long swimming hairs on the meso- and meta-tarsi, but in the more terrestrial subgenus Empleurus Hope, 1838 these are replaced with short and stiff setae. Identification to the subgenus level is generally straightforward but beyond this, to the specific level, it can be very difficult and many specimens will need to be dissected. The adults of all species, so far as is known, are vegetarian.
The larvae of the subgenus Empleurus have formerly been serious pests of various crops in the U.K. H. nubilus Fabricius, 1776, The Wheat Shoot Beetle, occurs in eastern parts of the U.K. while H. porculus Bedel, 1881 and H. rufipes (Bosc d’Anctic, 1791), The Turnip Mud Beetles, both occur sporadically throughout.
The subgenus Cyphelophorus Kuwert, 1884 contains a single very distinctive species, C. tuberculatus Gyllenhal, 1808, which occurs among peat and moss etc, it is entirely black with several series of shiny tubercles along the elytra and resembles charred wood in the field.
Our remaining species are associated with wetland habitats. Many are attracted to light, and during the day will come to polarized light, alighting on vehicle surfaces and puddles etc. Adults are easily found by sweeping vegetation and dipping among well vegetated marginal areas, searching cattle troughs and ponds etc. and flooded tyre ruts in woodland areas can be very productive in the spring. They will often be found encrusted in substrate among the roots of marginal plants. The adults are generally aquatic, or mostly so and will therefore occur by general pond sweeping. The eggs are enclosed in a silky cocoon and placed out of the water among soil etc, especially among vegetation; an exception to this is H. laticollis Thomson, C.G., 1854 which places them on vegetation emerging from the water. The larvae live among marginal soil and are predacious, only those of the terrestrial species are vegetarian.