Paromalus Erichson, 1834
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POLYPHAGA Emery, 1886
HYDROPHILOIDEA Latreille, 1802
DENDROPHILINAE Reitter, 1909
PAROMALINI Reitter, 1909
P. flavicornis (Herbst, 1791)
P. parallelepipedus (Herbst, 1791)
Paromalus Erichson, 1834 is an almost cosmopolitan genus of more than 60 species; 8 are recorded from the Nearctic region and 12 from the Palaearctic region and none have a Holarctic distribution. The European fauna includes 5 species, of which P. luderti Marsuel, 1862 is restricted to Spain and France, P. simplicistriatus J. Schmidt, 1885 is endemic to Greece and Turkey, and P. filum Reitter, 1884 is widespread in southern Europe. Two species are very widely distributed and generally common through Europe and Asia: P. flavicornis and P. parallelepipedus Herbst, 1791.
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Paromalus flavicornis (Herbst, 1791)
Widely referred to in older literature as Microlomalus flavicornis, this species is generally common throughout Europe as far north as southern Fennoscandia and the UK and east to Turkey, it is also widespread in north-western Africa and is known from Afghanistan and India. It is generally common across England north to south Yorkshire though largely absent from the West Country and known from only a few records in south and eastern Wales. Habitats include established woodland and wooded parkland with plenty of trees in various stages of decay, although adults will often be found on individual trees in hedgerows and gardens etc. Adults occur year-round, they peak in abundance during spring and autumn but may be common and remain active through the winter; they are nocturnal and are among the earliest of beetles to be seen on logs and trunks by torchlight, they otherwise remain under bark and often occur in numbers. Host species include a wide range of broadleaved trees, and on the continent also from Pine (Pinus sylvestris L.) Adults occasionally occur among soft decaying wood or in old bird nests, they sometimes live in association with various ants e.g. Lasius fuliginosus (Latreille, 1798) or Formica cunicularia Latreille, 1798; and often appear among winter extraction samples of bark debris etc, they frequent sap runs and may occur in numbers on cut stumps and trunks where the sap is still oozing. Both adults and larvae are predominantly predatory on other saproxylic insects, adults often occur in stag beetle and longhorn borings, and larvae develop mostly in bark beetle (Scolytinae Latreille, 1804) galleries although on the continent they are also recorded from burrows of Bostrichus capucinus (Linnaeus, 1758). Sampling is easiest by searching at night; with a little experience the elongate, flattened form and shiny appearance is distinctive, but they usually occur along with other tiny saproxylic beetles and so at first will need to be taken for critical examination.
1.8-2.5 mm. Elongate-oval and continuous in outline; broadest about the middle and narrowed to the head and the elytral apices, body shiny black and glabrous, appendages pale brown throughout. Head transverse from above, flattened dorsally and finely punctured throughout, eyes transverse and weakly convex; almost continuous with the outline. Antennae inserted in small scrobes near the base of the eyes, 11-segmented with a long, curved scape and round 4-segmented club. Pronotum transverse and smoothly narrowed from perpendicular posterior angles to slightly projecting anterior angles, surface evenly convex and finely punctured throughout. Prosternum with a distinct gular lobe projecting under the head, this is deeply incised laterally to accommodate the antennal scape and funiculus, basal third with cavities behind the coxae to accommodate the antennal club. Anterior mesosternal keel obtusely angled either side of the middle. Elytra narrowed from the basal third to a continuously-rounded apical margin which leaves the terminal one or two tergites exposed, surface randomly punctured throughout and lacking striae although there is usually a weakly-defined partial stria in the basal third above the shoulders. Femora narrowly visible with normal setting. Front tibiae broad and parallel-sided in the apical half; in fresh specimens with an obtuse angle about the middle and three or four external teeth and a sharp apical spur. Middle tibiae gradually broadened to the middle then parallel-sided to truncate apices; in fresh specimens with several fine external teeth in the apical half. Hind tibiae smooth and only weakly broadened beyond the middle. Tarsi 5-segmented and simple.
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Paromalus parallelepipedus (Herbst, 1791)
This is the more common of the two widespread European species, especially in more temperate northern regions where it extends into middle latitudes of Fennoscandia, to the east it extends into China and Japan and it is therefore the most widespread member of the genus. It was recorded from the UK (Glamorganshire) in the 1920s but these specimens are thought to have been imported and several other older records are thought to be based on misidentified specimens of P. flavicornis, it is now included in the UK list from several specimens found in East Anglia over recent decades but whether these represent stable populations is not known. In northern Europe it is very common in conifer woodland and plantations where it occurs mostly under the bark of Pine and Spruce and less frequently other conifers and occasionally various broadleaved trees such as Beech, Oak and Willow, the UK records are from fallen Scot’s Pine trees and Pine logs. Adults occur year-round and are active over a very long season although in the UK they have only been recorded during spring and summer; they are crepuscular and nocturnal, often appearing in numbers on trunks and logs during spring and late summer, but by day remaining hidden under bark or among decaying wood. The predatory larvae develop through the summer and have been recorded in abundance in bark-beetle galleries across northern Europe, they pupate under bark in the summer and new-generation adults appear from late summer. Numbers fluctuate in line with populations of bark beetles and in northern conifer plantations they are an important component of natural control; it is likely the species is a specialist predator as adults have occurred in pheromone traps designed to attract a range of bark beetles. Adults are good fliers and are quick to arrive at new scolytid infestations.
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1.5-2.2 mm. Very similar to P. flavicornis but the form is less curved laterally; there is often a slight but distinct constriction where the pronotum and elytra meet, and the elytra are generally broadest about the middle but both species vary and are easily mistaken in these respects. Specimens can be reliably separated by the form of the transverse keels towards the anterior margin of the mesosternum; in the present species they project acutely or perpendicular towards the base of the mesosternum (like an M with curved lines) whereas in flavicornis the form widely obtuse angles which only weakly project forwards.