Heterocerus obsoletus Curtis, 1828
POLYPHAGA Emery, 1886
BYRRHOIDEA Latreille, 1804
Heterocerus Fabricius, 1792
This is generally rare in Europe; it is mostly halophilic and coastal but it sometimes occurs at the margins of freshwater ponds and ditches etc. There are scattered inland sites across Europe, generally near salt pits and workings, but the majority of records are coastal from Western France to the Baltic, it is locally common around the southern coasts of Norway, Sweden and Finland, including Gotland, but is otherwise generally absent from the Baltic region. To the south there are scattered records from Southern France to the northern shores of the Black Sea, and beyond this the species has been recorded to the far east of the Palaearctic region. In the UK it is very local and scarce, it occurs more or less continuously along the coast from the Wash to Kent and there are further coastal records from West Sussex, IOW, North Somerset, and south and western Wales, beyond this there are widely-spaced records across the midlands as far north as Nottingham. The typical habitats are silty brackish pools with dense but patchy vegetation, salt marsh margins and drainage ditches etc., but inland sites seem to be fresh water remote from any obvious saline influence. Adults have been recorded from all months and it is likely that winter is always passed in this stage; they are otherwise active from early spring until the first frosts of autumn, peaking in abundance during June or July. Adults spend most of their time burrowing among damp or wet marginal sediments but they emerge and roam on the surface during the warmest days and dispersing swarms may appear in spring or late summer. Both adults and larvae are thought to feed on algae and organic matter as they burrow through sediments. Breeding occurs in the spring and females dig short burrows into wet sediment to lay eggs in small chambers. Larvae have a similar lifestyle to the adults and both stages have been found in the same burrows, they develop rapidly and pupation occurs from June or July to produce new-generation adults from July and August. Adults can be sampled by sieving or washing fine substrates but with experience the raised tracks from their burrowing become obvious although identification can be tricky and several species often occur together. Rapid and very good results can be obtained by flooding small areas of sediment and waiting for the beetles to emerge, which they soon will and usually in numbers.
© Lech Borowiec
4.3-5.8 mm. Very typical of the genus; elongate and parallel-sided with dense dorsal pubescence and drab colouration. The dorsal pubescence appears long and dense but consists of three distinct layers produced by hairs of differing length, it is mostly dense and grey, especially on the head and pronotal margins, but is mixed with longer and darker hairs throughout. Head dark grey to almost black, pronotum dark grey with pale marks inside the anterior angles, this pale colour may extend along the lateral margins towards the centre, elytra dark with obscure and usually small pale spots which, apart from a small spot near the scutellum, are usually absent from the basal third. Antennae highly modified; 11-segmented with a compact 7-segmented club and dark with several pale basal segments. Legs mostly dark, sometimes the femora are paler about the centre and the tarsi may be partly or entirely pale. Pronotum transverse, broadest across rounded posterior angles and narrowed to slightly projecting anterior angles, basal margin curved and finely bordered, apical margin almost straight, surface microsculptured and finely punctured, usually appearing duller than the elytra. Elytra almost parallel-sided from rounded shoulders to a continuous apical margin which completely covers the abdomen, surface rough and finely punctured throughout, without striae but usually distinctly longitudinally depressed inside the shoulders. In most specimens the pale elytral markings are small and obscure or at least ill-defined, they usually form two irregular transverse bands, one before and one after the middle, and there are usually more pale spots about the apex and lateral margins, in rare cases there is a U-shaped band in the basal third. Epipleura smooth, without an oblique ridge behind the humeral angle, and almost entirely dark. The first abdominal sternite bears a stridulatory ridge (which can be obscured by the hind femora), this appears as an oblique line extending from the lateral margin at the base and ending towards the centre of the apical margin, it does not recurve towards the base. This last character will distinguish all Heterocerus from species of Augyles Schiodte, 1866.