Glischrochilus Reitter, 1873
POLYPHAGA Emery, 1886
CUCUJOIDEA Latreille, 1802
CRYPTARCHINAE Thomson, C.G., 1859
GLISCHROCHILUS Reitter, 1873
LIBRODOR Reitter, 1884
Members of this genus are often referred to as Ips or Librodor. Glischrochilus is a small cosmopolitan genus with the greatest diversity in Southeast Asia; there are about 30 Palaearctic species and a dozen or so in the Nearctic region. They are poorly represented in the Australian, African and Neotropical regions and only 5 species occur in Korea. They are among the largest and most readily recognisable of the Nitidulidae; broadly oval, rather convex and black with distinctive red or yellow markings to the elytra. The genus is divided into 2 subgenera; Glischrochilus s.str. and Librodor Reitter, 1884 which contains the majority of the species. Both have a Holarctic distribution. Species of Glischrochilus s.str. are generally saproxylic, living beneath dead or damaged bark on a range of deciduous and coniferous trees, both as larvae and adults, where they are facultative and obligate predators of other insects and their larvae. Some species have occasionally been introduced into new areas to help control scolytid pests etc. They fly strongly, are quick to colonize new areas, and may quickly appear in large numbers as they are attracted to pheromones used by bark beetles. Members of the subgenus Librodor feed on a range of plant products; in the wild typically on exuding sap from injured trees, decaying vegetation and fungi but they are strongly attracted to fermenting products of all kinds e.g. alcoholic products, vinegar and fruit juices which has earned them the common names of picnic beetles or beer bugs. They are readily surveyed using traps baited with molasses, pineapple or vinegar etc. Some are considered economic pests, although not in the U.K., of fruit and vegetable crops e.g. strawberries, tomatoes, apricots and peaches etc. and may become a serious problem when fruits become over-ripe or damaged. They are also known to assist in the spread of pathogenic plant fungi such as Fusarium and Ceratocystis. They are generally difficult to control as they are very strongly attracted to the small of fermenting products and they are hugely fecund.
In general the eggs are elongate and white and laid among suitable decaying plant material or under bark etc. in the spring. Larvae develop rapidly, usually taking about a month from hatching to pupation. New generation adults appear in the spring and there is a single generation each year.
The species of both subgenera are oblong, glabrous and shiny. In some species the outline is discontinuous with the base of the pronotum narrower than the elytral base, and this may be an adaptation allowing some articulation in species that live under bark. In general they are black with 2 or 4 discreet yellow, orange or red markings to the elytra but this pattern sometimes varies e.g. G. vittatus (Say, 1835), a Nearctic species found under pine bark, has attractive yellow streaks to the elytra, and in some the margins and apex of the elytra are pale. The entire upper-surface is finely to moderately strongly punctured. Size variable, some species are among the largest of the family, 3-12mm. Head large and broad, usually with large, convex eyes. The labrum is short and fused to the clypeus. The antennae are short, about as long as the head; basal segment long and convex, second rounded and shorter than the third, 3-8 progressively shorter and more convex towards the apex. The last 3 form a moderately compact club. Antennal grooves visible in side view and generally curved down in front of the eyes. Mandibles asymmetric; bifid at the apex and interlocking when closed, robust and produced forward, usually visible from above. Palpi short, the first segment as long as the first, and the second longer than the third. Mentum strongly transverse and deeply emarginate anteriorly. Pronotal base as broad as or a little narrower than the elytral base. Lateral margins strongly bordered and often narrowly explanate, the base variably bordered and usually sinuate. The front margin generally without borders and the front angles produced. Scutellum usually small, equilateral or transverse and to some extent punctured, sometimes only at the base. Elytra entire, exposing at most a part of the pygidium. Generally with traces of striae among the random punctures, and a sutural stria is usually distinct towards the apex. Shoulders generally distinctly toothed and lateral margins explanate to the apical angle. Apices weakly curved and truncate or separately rounded. Anterior coxal cavities open behind. Prosternal process laminiform, produced behind the coxae but not reaching the mesosternum. First abdominal sternite about as long as the next 3 combined, the fourth longer than the third. Legs robust with the tibiae generally curved outwards towards the apex and a spine on the inner apical angle. Tarsi 5-5-5. Basal segments bilobed, strongly so on the pro tarsi, and often sexually dimorphic, being broader in the male.
Three species occur in the U.K. and they may be identified from the following key:
Body outline discontinuous; pronotum narrowed towards the base where it is distinctly narrower than the elytra across the shoulders. Apex of prosternal process truncate or nearly so. Overall more parallel-sided and flattened, the elytra not so gradually contracted towards the apex. Elytral maculae red; the anterior transverse, irregular in shape and produced forward, the posterior more regularly transverse than in the other species. 3.5-6.0mm.
Body outline continuous; the width of the pronotal and elytral bases more or less equal. Apex of prosternal process semicircular. Overall more convex, the pronotum and elytra less parallel and more contracted towards their apices.
Elytral maculae pale, the anterior obliquely transverse, sharply angled, irregular and distinctly produced forward. 3.0-5.0mm.
Elytral maculae red, the anterior an oblique parallelogram, without sharp angles or a forwardly produced lobe. 4.0-6.0mm.
Among the British fauna they might be confused with the larger spotted Mycetophagus species which are nocturnal and occur at fungi but they lack the well-defined antennal club of Glischrochilus and have distinctly striate elytra.
Glischrochilus hortensis (Geoffroy in Fourcroy, 1785)
This widespread European and Asian species occurs sporadically throughout the U.K. It is relatively common in the English midlands but local elsewhere and apparently absent from the West Country. The typical habitat is woodland where the beetles feed on sap, ripe fruit and decaying fungi but they may occur in many situations including urban gardens where they may inhabit compost heaps etc. and we have found them in numbers among excavated and decaying water-lily roots beside a gravel-pit in St. Albans, South Herts. Beyond this they are strongly attracted to fermenting vegetable matter and so may occur in just about any situation. Adults are present year round but are mostly active from April to October when they may be surveyed using molasses baited traps. They are active nocturnally and may be found during the day among their food source, when found they are usually present in numbers. On the continent they are surveyed in broadleaved and coniferous woodland using aerial traps baited with beer.
4.0-6.0mm. Black and shiny with the tarsi and at least the middle antennal segments red. Upper surface entirely finely and quite closely punctured. Head relatively large, more especially so in the male. Eyes weakly convex and protuberant. Antennal grooves distinct in side view. Clypeus variable; weakly to strongly emarginate anteriorly. Mandibles robust and asymmetric at apex. Pronotum transverse and convex, lateral margins distinctly bordered and weakly explanate. Anterior margin not bordered, front angles produced forward. Basal margin sinuate and bordered. Scutellum transverse, black with the apex pale, and punctured along the base. Humeral angle of elytra toothed. Lateral margins of the elytra explanate almost to the apex, apices separately rounded. Surface randomly and finely punctured and with traces of striae, a sutural stria is well impressed towards the apex. Apical margins rounded leaving most of the pygidium exposed. All tibiae sinuate and broadly expanded toward the apex and with a strong spine on the inner apical angle; mid and hind tibiae with rows of fine spines externally. Basal tarsal segments dilated, more so in the male, the fourth segment tiny but distinct, the fifth long and expanded towards the apex. Claws smooth and not toothed at the base.
Glischrochilus quadriguttatus (Fabricius, 1777)
This is another widespread Palaearctic species occurring throughout Europe and east to Russia and Northern Siberia. Typical of the subgenus Librodor this species has much the same habits and ecology as G. hortensis but it has a more local and sporadic distribution with records scattered northwards to the Scottish borders. In continental Europe it is common in decaying fungi on both broadleaved and coniferous trees. In Ireland it is associated with Fraxinus.
3.0-5.0mm. Entirely shiny black with the antennae, except for the club, and the legs mostly pale. Head broad with prominent and very convex eyes, produced forward in front of the antennal insertions. Surface quite strongly but sparsely punctured. Antennal scrobes distinct in side view. Mandibles strongly curved and asymmetric at the apex. Clypeus weakly emarginate anteriorly. Pronotum transverse, convex and strongly bordered laterally, anterior margin simple and the front angles produced forward. Basal margin sinuate and with weakly obtuse hind angles Scutellum large, equilateral and finely punctured; dark with the apical margin pale. Shoulders of the elytra with a small tooth, lateral margins explanate almost to the apex. The surface finely and randomly punctured, with traces of striae but a sutural stria is distinct towards the apex. Apical margins weakly rounded and truncate, leaving most of the pygidium exposed. Tibiae gradually expanded towards the apex and with a strong spur on the inner apical angle. Middle and hind tibiae with rows of fine spines along the outer edges. Basal segments of the front and middle tarsi dilated, more so in the male, fourth segment small but distinct and the claw segment long and gradually expanded towards the apex. Claws smooth and without a basal tooth.
Glischrochilus quadripunctatus (Linnaeus, 1758)
This widespread Palaearctic species occurs in suitable habitats throughout Europe and east to Siberia. In the U.K. it is widespread but very local north to the Scottish Highlands, but absent from the West Country and much of Wales. Abroad it may be found on a range of broadleaved and coniferous trees but in the U.K. it is almost entirely associated with conifers. Both adults and larvae predate other insects under bark. The adults are nocturnal and have been recorded at sap and fungi, during the day they are occasionally recorded in flight on woodland margins or in clearings during hot weather. They generally occur in numbers.
3.5-6.0mm. Black, or nearly so, but for the elytral markings. Entire upper surface finely and moderately densely punctured. Head large with long, rounded temples and the clypeus produced in front of weakly convex eyes. Mandibles strongly curved and sharp, the apex bidentate and asymmetric. Basal segment of the antennae long and curved, the club distinctly demarked. Pronotum transverse, bordered laterally and basally and with produced front angles. Sides more or less straight anteriorly then evenly contracted to obtuse hind angles. Base distinctly narrower than the elytral base. Scutellum transverse, punctured towards the base, and lighter at the apex. Elytra more parallel sided than our other U.K. species, lateral margins explanate almost to the apex and only weakly curved, the apical margins separately and strongly rounded. Surface with traces of striae among the punctures, sometimes well-developed on the disc, and a sutural stria usually well impressed towards the apex. Red markings large; the anterior usually with 3 distinct and broad lobes, the anterior lobe almost touching the elytral base. Legs rather slender; tibiae greatly expanded towards the apex and toothed on the inner apical angle. Front tibial margins strongly sinuate. Basal tarsal segments dilated, on the pro-tarsi strongly so, fourth segment small but distinct and the last segment very long with robust and smooth claws.