Helophorus nubilus Fabricius, 1777
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POLYPHAGA Emery, 1886
HYDROPHILOIDEA Latreille, 1802
Helophorus Fabricius, 1775
Empleurus Hope, 1838
This species is locally common throughout Europe north to the UK and into southern Fennoscandia and extending east as far as Turkey and European Russia, there are also records from India and Siberia but these may be doubtful, it occurs mostly in lowland situations although in parts of Europe extends above the tree line in mountain areas. In the UK it is locally common across southeast and central England but more sporadic and generally scarce further north into southern Scotland and in Ireland. Atypical of the genus this species is generally associated with grassland and damp heathland although at higher altitudes it often occurs under decaying plant debris beside streams and among vegetation stranded by flood surges etc. Adults occur through from spring until the autumn and specimens are occasionally recorded through the winter, the typical habitat is open grassland, often on dry sandy or clay soil exposed to the sun, and cultivated land where they are occasional pests of various crops; in the UK there were serious infestations on farmland in the east of England during the early twentieth century but nowadays this is very rare. Mating occurs in late summer and females oviposit in the soil during the autumn. Larvae develop through the autumn and winter and will feed during even the coldest of days; they initially feed on buried grass or other organic matter and then transfer to the base of grass shoots or cereal seedlings, in northern Europe often attacking wheat. The first instars bite into the base of shoots and feed externally, they do not enter the plant but remain in the soil and may move between shoots, leaving ragged holes in the stems which usually turn brown and often die-off. Larval feeding usually commences in November and continues into the following spring, pupation occurs in the soil during April and May and new-generation adults occur from early May. Adults can fly but rarely do so, they may be sampled by sweeping of taking samples of suitable material but like the larvae, they are mostly crepuscular and nocturnal and so may occur in numbers in pitfall traps, they have also been recorded from the nests of various ants.
3.0-4.5 mm. Long-oval and discontinuous in outline, head dark brown or black, pronotum dark brown with paler lateral and apical margins, elytra mottled with dark and pale brown, usually forming a symmetrical pattern, appendages pale brown. Head transverse with protruding convex eyes and smoothly convex clypeus (in some other species this is raised anteriorly), surface distinctly granulate, the Y-shaped impression variable but usually weakly defined. Pronotum transverse, broadest behind strongly protruding anterior angles and narrowed in a more-or-less straight line to obtuse posterior angles, apical margin strongly bisinuate, surface with distinct granulation and well-impressed longitudinal furrows which are only slightly narrowed towards the base; the central furrow wide and straight, the second (sub median) distinctly angled and the outer (sub marginal) sinuate. Elytra with rounded humeral angles and broadest behind the middle, striae, including a scutellary striole, well-developed and odd-numbered interstices raised, each with a series of small stiff setae which are larger than those on the other interstices, the third depressed but not interrupted in the basal third. Legs long and slender, tibiae lacking external teeth or spines and with fine terminal spurs, tarsi with five simple segments.
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Among our UK species only H. rufipes (Bosc d’Antic, 1791) and H. porculus Bedel, 1881 have the strongly sinuate anterior pronotal margin and raised elytral sculpture. Both are on average larger but they overlap, in H. rufipes the lateral pronotal margin is distinctly sinuate and the elytral humeral angle is sharp and slightly acute while in H. Porculus the clypeus is raised anteriorly and the inner pronotal furrows are strongly narrowed towards the base.