LACCOPHILINAE Gistel, 1848
Of the three British species L. poecilus is very rare, while the other two are more widespread, L. minutus in standing water and L. hyalinus in running water.
This is a relatively small subfamily of about 460 described species, it is cosmopolitan in distribution due to the largest genus, Laccophilus Leach, 1815, which includes almost 300 species and occurs worldwide although the greatest diversity is in tropical regions and temperate region are only poorly represented. The subfamily includes 14 genera in 2 tribes and other than Laccophilus all are of rather restricted distribution. The Agabetini Branden, 1885, sometimes considered as a separate subfamily, includes two species of the single genus Agabetes Crotch, 1873; one from Iran and one Nearctic, they are atypical of the group, resembling small Agabus. Species of Laccophilini Gistel, 1856 form a very distinctive group within the Dytiscidae (see below) although some faunas are relatively poorly known, especially from the Neotropics, and many more no doubt await discovery. Temperate regional faunas generally include only species of Laccophilus e.g. about 30 species occur in the Nearctic region but only 4 extend north to Canada (about 100 occur in the Neotropical region), the Nearctic fauna otherwise includes only a single species of Laccodytes Régimbart, 1895, a genus of 11 species otherwise restricted to the Neotropical region. The European fauna includes only 4 species of Laccophilus, and beyond Laccophilus the Palaearctic fauna includes the monotypic Laccoporus J. Balfour-Browne, 1939 from Tibet and the monotypic Japanolaccophilus Satô, 1972 from Japan. Tropical regions are diverse though the genera are usually restricted, only Neptosternus Sharp, 1882, with about 100 species, is widespread across Africa and Southeast Asia. The African endemics include the monotypic Philodytes J. Balfour-Brown, 1939 which extends north to the Mediterranean but not Europe, 5 species of Philaccolus Guignot, 1937, and about 20 species of Africophilus Guignot, 1948, the African fauna otherwise includes >100 species of Laccophilus. Other Old World genera are Australphilus Watts, 1978, with 2 species from southeast Australia, Philaccolilus Guignot, 1937 with 12 species from New Guinea, and Laccosternus Brancucci, 1983 with 2 species from Southeast Asia. The Oriental region includes about 50 species of Laccophilus while about 12 occur in New Guinea and 8 have been recorded from Australia. Two genera are restricted to the Neotropics; the monotypic Napodytes Steiner, 1981 is endemic to Ecuador and about 12 species of Laccomimus Toledo & Michat, 2015 occur in central and South America.
Adults occur in a wide variety of slow moving and standing water, in acid as well as basic conditions and in salt marshes, most species may be found among sparse vegetation in permanent ponds and lake margins or slow moving stretches of rivers but they also occur in temporary pools devoid of vegetation, they commonly occur in unshaded situations such as moorland ponds but may also occur in heavily shaded woodland ponds. They are generally easy to sample by sweeping and at certain times of the year, especially in spring and early summer, adults may occur in numbers, flight ability varies between species but at least some are good fliers, they may be quick to colonize new habitats and some occur in light traps. The general life-cycle is univoltine with overwintered adults breeding in spring and early summer and the new generation appearing in late summer and autumn. Adults will soon become familiar in the field but a good guide to their presence is their ability to jump vigorously in the pond net, this is a specialized behaviour where they lock a small notch on the metafemora onto a projection on the dorsal surface of the metacoxae and release the energy like a spring, propelling them forward and upward.
Members are small to medium sized beetles ranging from 1.5mm (Laccodytes and some Africophilus) to about 8.5mm (Laccophilus) but most are between 3 and 4mm, they are continuous in outline and have a distinctive broadly-oval shape which is broadest before or around the middle and acuminate apically. All are glabrous and many are drab and mottled pale and dark grey but some have distinctive markings e.g. the dark transverse elytral fascia in Laccophilus fasciatus Aubé, 1838, or the brightly patterned elytra of e.g. L. maculosus Say, 1823 or (especially) L. pictus Laporte, 1835, and in many the head and pronotum are pale and contrast against darker elytra. The group is defined by a modified genital appendage in the female which forms a serrate ovipositor, this is also present in Agabetini but the tribes are otherwise very different and the following description refers to the Laccophilini, and Laccophilus in particular. Head deflexed and more or less hypognathous, widely transverse and only narrowly visible from above, the lateral margins occupied by large eyes which are smoothly convex but do not protrude and partly hidden by the anterior pronotal margin, the vertex is smooth or has shallow and poorly-defined impressions and from above the clypeal margin is smoothly curved. Anterior margin of the eyes emarginate, usually smoothly and shallowly curved behind the antennal insertions, antennae long and filiform. Pronotum transverse and broadest across the base, smoothly convex and lacking raised borders, anterior angles rounded from above, and posterior angles acute but not produced. Prosternal process long, sharp and not raised above the surrounding cuticle. Scutellum hidden by the medially produced basal margin of the pronotum. Elytra broadest in the basal half or at the middle and evenly curved to an acuminate apex, without striae but often with one or two rather random rows of small punctures from the base, surface very finely puncture and with single or double micro-reticulation, epipleura usually present only towards the base and strongly reduced before the middle, sub-lateral row of fine setae present in the apical half. Metasternum with narrow, arcuate lateral ‘wings’ and anterior margin produced medially, sometimes notched to accommodate the tip of the prosternal process, metacoxal process sub-parallel anteriorly and divergent apically, partly covering the meta-trochanters, metacoxae sometimes with a stridulatory file. The file produces sound or vibrations when rubbed against a similar structure on the posterior surface of the metafemur, in some species it is present only in the male while in others it is present in both sexes. Apical abdominal sternite rounded, truncate or notched, sometimes longitudinally impressed. Front and middle legs slender and relatively short, tibiae with paired spurs, tarsi with 5 simple segments and paired claws. Hind legs long and robust, the long femora not usually visible from above, tibiae with two large terminal spurs which are bifid apically-this character will distinguish Laccophilus from the other genera within the subfamily where they are apically simply acute-and in many there is a dorsal row of setiferous punctures. Hind tarsi with 5 visible and obvious segments, the basal three or four with the outer apical margin produced backwards. The terminal metatarsomere in the male is emarginate apically and bears a single small claw, in the female it is rounded apically and bears a much longer claw. Males may also be recognized by the lobed basal protarsomeres but they are laterally compressed and may be difficult to appreciate without manipulating a specimen under high magnification.
Adults may be recognized among the Dytiscidae by the combination of 5-segmented tarsi, the basal metatarsomeres being produced laterally at the apex, and the lack of a visible scutellum. Of the four European species of Laccophilus only L. biguttatus Kirby, 1837 does not occur in the UK, this is a widespread Holarctic species with a restricted and mostly northern distribution in Europe; in Scandinavia associated with densely vegetated brackish water in sheltered situations but further south in peat land ponds etc. Adults are distinctive in having a pale pronotum, pale elytra with a narrow dark sutural line and single-mesh microsculpture, a weakly produced pronotal basal margin and lacking a metacoxal stridulatory file.
Laccophilus minutus (Linnaeus, 1758)
This widespread and generally common species occurs throughout Europe north to the UK and the south of Fennoscandia, it also occurs in North Africa and is present on most of the Mediterranean islands, further east it ranges across Siberia and occurs in Sumatra and Java. Here it is our most common member of the genus, it occurs throughout England and Wales, including all the islands, and across Southern Scotland north to the Cairngorms. Adults typically occur in sparsely-vegetated permanent lowland ponds and lake margins, less often in slow-moving stretches of rivers and drainage ditches, they are present year-round and are good fliers, sometimes coming to light in the spring and early summer. Mating occurs in the spring and early summer and larvae develop through the summer to produce adults in late summer and autumn. Sweeping among sparse marginal vegetation or in shallow margins of unvegetated ponds is the easiest way to record this species, they usually occur in unshaded situations and they are often present in numbers, but we have also recorded individual specimens from temporary ponds in wooded situations in the New Forest.
Adults are readily distinguished from our other species by the large size, 4.3-4.8mm, and smooth hind coxae i.e. lacking a stridulatory file-this character must be looked for carefully as it may be hidden by the hind legs but its presence or absence will be obvious. Head and pronotum pale brown, at most with vague darker areas but without distinct markings, antennal and palps pale with the distal segments darker apically, elytra pale brown with darker longitudinal markings which may be extensive and so give the beetle a bicoloured appearance, ventral surface pale to dark brown, sometimes appearing distinctly reddish. In life the dorsal surface often has a greenish or even bronzy appearance and specimens need to be seen submerged to appreciate the colour and pattern. Dorsal surface with irregular double reticulation which may be very faint on the pronotal disc and at the elytral base. The base of the pronotum is strongly and rather abruptly produced backward at the centre, much more so than in our other species. Legs entirely dark reddish-brown. Males may be recognized by the dilated basal pro-tarsal segments, these are laterally compressed and so need to be examined in side view.
Laccophilus hyalinus (De Geer, 1774)
This species is locally common throughout the Palaearctic regions except for the far north, it occurs in North Africa and the Near East and is present on most of the Mediterranean islands although Mediterranean populations are sometimes referred to as L. testaceus Aubé, 1837 which differs slightly in colour but is probably conspecific. In the UK it is locally common in lowland water bodies across south and central England north to Lancashire and North Yorkshire; it is generally much more local and scarce in Wales and the West Country and sporadic and rare further north to the Scottish border. The typical habitat is sparsely vegetated slow moving canals and rivers, less often in lake and reservoir margins and occasionally around the margins of reed beds. Adults occur year-round, overwintered adults reproduce in the spring and early summer and larvae develop through the summer to produce new-generation adults from late summer. They are easily sampled by sweeping marginal situations and they will generally occur in numbers, they fly well and occasionally come to light on warm spring and summer evenings.
Readily recognized among our European fauna by the presence of a stridulatory file on the hind coxae, this is a transverse or oblique series of short longitudinal lines starting at the metasternal process and ending about half-way across the coxae, they may be hidden beneath the femora and so the legs may need to be moved to be sure of this structure. 4.6-5.1mm. Head, pronotum and appendages pale brown, distal segments of the antennae and palps darkened and sometimes the anterior and posterior margins of the pronotum are obscurely darker, elytra pale brown with various longitudinal darker markings that are often confluent and form discrete basal and lateral pale areas. Dorsal reticulation double, the finer meshes often very finely impressed and sometimes almost absent on the head and pronotum. Posterior margin of the pronotum only weakly produced medially, contrasting with the strongly produced margin seen in L. minutus. Basal pro-tarsal segments only weakly dilated in the male, these are laterally compressed and must be viewed from the side.
Laccophilus poecilus Klug, 1834
A very widespread species occurring throughout the Palaearctic region, extending south to North Africa and the Caucasus and north to the UK and the south of Sweden where it is rare and mostly coastal, occurring among dense vegetation in brackish water. In Europe it occurs in a wide range of habitats e.g. in Poland it is associated with peaty areas and especially sphagnum bogs but also in ponds and larger still-water bodies but further south, towards the Mediterranean, it occurs also in base-rich pools. In the UK it was formerly a very rare and local species of densely-vegetated lake margins and drainage ditches in near-coastal localities from Kent to South Hampshire, it was also present at a single site in Southwest Yorkshire where it occurred in pools on peaty substrates for much of the twentieth century, but it has not been recorded in recent decades and may now be locally extinct. Adults have been recorded in the UK throughout the year with the exception of a few weeks in early spring and new-generation specimens emerge in the summer and go on to overwinter which might suggest a univoltine life cycle with reproduction occurring in the winter. Adults are fully-winged and known to fly.
This species is readily identified by the small size, 3.4-4.0 mm, and lack of a stridulatory file on the hind coxae, the colouration is also distinctive. Head pale brown, often with the basal margin darkened although this is variously hidden by the anterior margin of the pronotum, palpomeres darkened apically, and antennae pale with distal segments darkened. Pronotum pale brown with a transverse dark mark behind the anterior margin about as wide as the distance between the eyes, basal margin entirely dark; broadly so about the middle and extending narrowly to the posterior angle. Basal margin broadly but not strongly produced along the centre. Elytra substantially dark with variously developed pale mottling which is usually more extensive laterally and apically, and two pale transverse bands, one oblique from the shoulder and another transverse in the apical third. Male with basal pro- and masotarsal segments dilated, these are compressed laterally and so must be viewed from the side.
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