COLYDIIDAE Billberg, 1820

Cylindrical Bark Beetles

Most species in this family are associated with decaying wood, being found under bark or in beetle galleries. Some species such as the eyeless Langelandia anophthalma have more specialized habits.

POLYPHAGA Emery, 1886 

TENEBRIONOIDEA Latreille, 1802

2

9

12

2.2-7mm

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Introduction

This group is more properly classified as a subfamily of the Zopheridae Solier, 1835 but for historical reasons i.e. that it has always been included in the UK checklist as a distinct family, we are including it as a family group. As such the composition has changed drastically over recent decades e.g. the Cerylonidae and Bothrideridae were formerly included, and the Pycnomerini Erichson, 1845 is often treated as a distinct tribe of the Zopherinae Solier, 1834. Beyond these rather major changes there have been numerous smaller ones and the group is likely to be revised further. As currently recognized the present group constitutes one of two subfamilies of the Zopheridae, with the Pycnomerini of doubtful placement. The Colydiinae Billberg, 1820 now includes 8 or 9 tribes, not including Pycnomerini, and about 140 genera; with the exception of the Synchitini Erichson, 1845 the tribes are small and often of limited distribution. Pycnomerini includes 4 genera, the large genus Pycnomerus Erichson, 1842, with about 50 species, is more or less cosmopolitan while the remainder, all small genera, are restricted to the Australasian region.

  • Acropini Sharp, 1894 includes 4 genera and is restricted to the Neotropical region. Most species are small but very distinctive with large, convex and posteriorly inclined eyes that give the head a typical cordate appearance. They are otherwise typical of the family with elongate, rather parallel-sided elytra with wide shoulders and a comparatively narrow pronotum, a broad head with large eyes and strongly narrowed temples. In most the dorsal surface is clothed with broad scale-like pubescence, often arranged in characteristic patterns, and various erect setae. The tarsi are slender and the antennae are either distinctly clubbed or distally thickened.

  • Adimerini Sharp, 1894 includes the monogeneric Stenomonoedus Heinze, 1954 from Ecuador, and Monoedus Horn, 1882 (formerly Adimerus Sharp, 1894) with 13 species distributed through the Caribbean although one, M. guttatus Horn, 1882, is now adventive in Florida. All are typical of the family and distinguished by the one-segmented antennal club and greatly expanded basal tarsal segment which often hides the second and third segment. In some systems Monoedus is included in the Synchitini.

  • Colydiini Billberg, 1820 includes 4 genera, all of which occur in the New World; 2 are Neotropical; Anarmostes Pascoe, 1860 with 6 species, and the doubtfully-placed Pseudaulonium Reitter, 1877 with 11 species, while Aulonium Erichson, 1845 and Colydium Fabricius, 1792 occur throughout the Nearctic and Western Palaearctic regions. The species are very characteristic; elongate and parallel-sided, glabrous or nearly so, with sub-lateral pronotal carinae, apically broadened and externally spinose pro-tibiae, 3-segmented antennal club and closed pro-coxal cavities. Both Palaearctic genera occur in the UK and a familiarity with these will allow the members of the tribe to be recognized.

  • Gempylodini Sharp, 1893. This is a pan-tropical tribe of 6 genera, the species are distinctive due to the very elongate and slender habitas and the form of the prosternal process; very narrow between the coxae and broadly expanded posterior to the coxal cavities. They are superficially similar to the Colydiini but lack the sub-lateral pronotal grooves.

  • Nematidiini Sharp, 1894 includes the single genus Nematidium Erichson, 1845, 11 species occur in the New World of which one, N. filiform LeConte, 1863, extends into the southern United States, and other species occur in the Australasian region. They are very elongate, thin and cylindrical, they lack pronotal sulci and are distinguished by the 11-segmented antennae with an abrupt 2-segmented club, the base of the mandibles being visible from above, the lack of supraorbital ridges and very finely bordered pronotal margins. The prosternal process is broad and flat and the pro-coxal cavities are closed posteriorly.

  • Rhagoderini Horn, 1878 includes the single genus Rhagodera Mannerheim, 1843 which is endemic to North America and Mexico, the greatest diversity is in Mexico and only 4 species occur in the southern USA. Species are more typical of the subfamily although the placement within the Zopheridae remains uncertain, broadly oval and strongly rugose or otherwise sculptured, with a pair of longitudinal ridges to the pronotum and 3 raised elytral interstices. The antennae are densely pubescent, 11-segmented with a very gradual and indistinct 3-segmented club, the eyes are small and coarsely faceted and the temples short and convex. Species are ground-living in desert regions; they are flightless and have fused elytra.

  • Rhopalocerini Reitter, 1911 includes 17 species of the single Old World genus Rhopalocerus Redtenbacher, 1842. The group is widespread with 5 species in Africa, 3 in Madagascar, and 8 in Indonesia; a single species, R. rondanii (Villa & Villa, 1833) is widespread though very rare in central and southern Europe. Adults are elongate-oval and superficially very typical of the subfamily, with heavily sculptured or coarsely punctured head, pronotum and elytra, the densely-scaled 10-segmented antennae are moniliform or have transverse segments, and a 1-segmented, distinct or indistinct, club. The basal tarsomere is reduced and so the tarsi appear to be 3-3-3 with a long and narrow terminal segment. Unusually, all possess a raised metasternal tooth anterior to the metacoxae. All species seem to be saproxylic; R. rondanii is generally associated with the tree-nesting ant Lasius brunneus (Latreille) on various deciduous trees.

  • Sarrotriini Billberg, 1820 this tribe, variously referred to as the Orthocerini Blanchard, 1845, includes 3 western Palaearctic genera. Diplagia Reitter, 1882 includes the single species, D. hellenica Reitter, 1882, known from Greece. Helioctamenus Schauffass, 1882  includes 11 species distributed in the warmer parts of Europe and North Africa, and Orthocerus Latreille, 1796 includes 2 European species, one of which O. clavicornis (Linnaeus, 1758) extends north to the UK. All are characterized by the antennal structure; heavily scaled and apparently 10-segmented but the eleventh segment is enclosed within the tenth and these appear as a one segmented club. All are brachypterous and ground-living, generally occurring under lichens etc. on sparsely vegetated and mostly sandy soils. The prosternal process is broad and apically emarginate and the pro-coxae are open.

  • Synchitini Erichson, 1845 includes the majority of the genera, about 115, and is virtually cosmopolitan in distribution.  Diversity is generally greater in warmer areas; 36 genera have been recorded from the Neotropical region, 19 from the United States and 6 from Canada. About 30 genera occur in the Palaearctic region and the group is represented on most of the world’s islands, New Zealand being particularly diverse with 23 recorded genera, about 35 genera being recorded from the Australasian region. Species are very diverse and the group has historically been used to accommodate many genera which do not fit into other tribes, the group is in need of revision but the general description given below along with the various pictures will give an idea of the group. Many species of the Synchitini i.e. the majority of the subfamily, are saproxylic and associated with decaying wood, bark and the fungi occurring in such habitats, both Basidiomycetes and Ascomycetes, and most are probably fungivorous, feeding and developing within fruiting bodies or among decaying organic matter hosting the fungi. Among the UK genera Synchita Hellwig, 1792, Pycnomerus Erichson, 1842 and Cicones Curtis, 1827 almost always occur on or near fungi although both adults and larvae of Bitoma are known to predate small invertebrates in such habitats. The impressively denticulate Endophloeus markovichianus (Piller & Mitterpacher, 1783) occurs among lichens, moss and fungus on decaying logs and stumps, though its inclusion on the UK list is based on old records from the New Forest and it is now considered to be extinct here. Many species occur among accumulated red- or white-rotten wood debris in tree hollows etc. and, among the group as a whole, many are known to be predatory either as adults, larvae or both but in most cases the early instar larvae are known to be fungivorous. On a world scale many species are terrestrial, living among decaying plant material or under leaf rosettes in arid areas, the terrestrial UK fauna includes Orthocerus, which occurs among lichens etc. on dry sandy soils, and Langelandia, which lives within the soil consuming decaying plant remains. Some species are specialist scolytid or ptinid predators and will usually be found within their galleries, the UK genera Colydium Fabricius, 1792 and Aulonium Erichson, 1845 fall into this category although in both cases they have also been observed feeding upon fungi or decaying plant material. Many foreign species are associated with the fruits or underground tubers of various plants.

Ecology

So far as is known species of the Adimerini are phytophagous or saproxylic with adults and larvae occurring in stems of herbaceous plants, and some have been beaten from old branches infected with fungi. Adults and larvae of Colydiini generally are known to be predatory on sub-cortical larvae and eggs etc. as well as being fungivorous in the early larval stages, when species of Scolytus began to destroy elm trees in the 1970’s many predatory beetles also increased in numbers and Aulonium trisulcus became locally common across the south of England. Species of the tropical group Gempylodini, in which adults are longer and thinner than those of Colydiini, are also known to be predatory in the galleries of bark beetles and are also to some extent fungivorous as larvae. Species of the Neotropical Acropini have very large and well-developed eyes and are known to be active on the surface of wood at night.

Description

Species vary from just over 1mm to about 15mm although the majority are less than 5mm. The group is morphologically very diverse but, allowing for the very elongate and narrow forms, most are fairly distinctive and a familiarity with the UK list will allow the majority to be recognized, many exotic forms are strongly developed in terms of dorsal sculpture; pronotal and elytral carinae and sulci, development of explanate margins and lateral teeth, scales, setae and tubercles etc. Antennal development is also very variable, probably most developed in Orthocerus Latreille, 1796, but always, if not always convincingly, clubbed. The majority of species display the following combination of characters: antennal insertions concealed from above, antennae to some extent clubbed, (apparently) 4-segmented tarsi and either the prosternal process is dilated to close the pro-coxal cavities posteriorly, or the cavities are open or otherwise closed. Species vary from very elongate, parallel-sided and cylindrical to broadly-oval and convex or flattened, most are dull brown to black in colour although some have bright red or yellow maculae or margins etc., and many have a mottled or longitudinal or transverse striped pattern caused by areas of contrasting pubescence or scales. Some groups are glabrous but most are pubescent, often densely so, this varying from fine and recumbent, often with more sparse stiff and erect setae, to dense and long, and in many groups these are developed into broad scales. Head prognathous and obvious from above; often coarsely sculptured and/or punctured and often with longitudinal carinae along the frons or beside the eyes; often extended in front of the eyes and with small temples. The eyes usually proportionally small, convex and entire although they are sometimes absent e.g. in Langelandia Aubé, 1843, and sometimes weakly or strongly emarginate or partly divided by a backward extension of the canthus. The small genus Lyreus Aubé, 1861 is interesting; these subterranean species are tiny and lack eyes, most occur in Western Europe; Sardinia, Spain and France but there is also a Nearctic member from a limestone sink-hole in Alabama. Antennae usually rather short and densely pubescent; 10- or 11-segmented with a 1- to 3-segmented club, or at least thickened apically, inserted under the anterior or lateral margins and often retracted into cavities below the eyes when at rest. Mouthparts very variable though often visible from above, maxillary palps 4-segmented, labial palps 3-segmented, the terminal segment in each case variable. Pronotum very elongate to quadrate or widely transverse, surface variously sculptured from smooth to strongly carinate or with tubercles, sulci or fovea, lateral margin smooth to strongly toothed, sometimes very strongly so near the angles, surface smooth, punctured, microsculptured or micro-tuberculate. Prosternum long and wide in front of open or, less commonly, closed coxal cavities, process narrow to broad between the coxae and sometimes expanded posteriorly to close the cavities. Hypomera smooth or with antennal cavities and sometimes expanded at the base to close the coxal cavities. Scutellum usually small and sometimes not visible. Mesosternum short, the intercoxal distance variable, and the coxae closed laterally. Metasternum broad and long in front of weakly to strongly transverse and closely approximated coxae, surface smooth, convex and variously punctured, often with a variable longitudinal impression from the apex and often emarginate to receive the produced basal abdominal sternite. Wings usually well-developed but often brachypterous or apterous in ground-living forms. Abdomen with 5 visible sternites; all free or with 1, 2 or 3 connate. Elytra entire, completely covering the abdomen and usually continuously rounded apically, with up to 11 striae although in many these are variously obliterated or developed into complete or partial carinae or depressions, and often tuberculate or otherwise sculptured. Lateral margins smooth or toothed, sometimes explanate; epipleura usually present, at least towards the base and only rarely absent. Legs generally short and slender; coxae often projecting, trocanters usually strongly oblique (heteromeroid), femora short and broad; usually smooth along the inner margin, tibiae usually slender and often with a strong apical spine, only rarely dilated apically or with external teeth. Tarsi 4-4-4, sometimes appearing 3-3-3 due to fused basal segments, various basal segments rarely expanded and densely pubescent below, terminal segment usually much longer than the others.

Larvae of this subfamily are elongate and subcylindrical to weakly flattened, straight or weakly curved and only sparsely pubescent, most are pale with the head and ninth abdominal segment darkened. The head is prognathous, transverse to weakly elongate and globular or slightly flattened, with a variable epicranial suture; the stem is usually short and the arms V-shaped or curved. The antennae are 3-segmented and well-developed or, very rarely, 2-segmented and short. Pronotum generally not wider than the head, the dorsal surface of the metathorax or sometimes that of the basal abdominal segment with patches or rows of small tubercles. The ninth abdominal segment is often distinctly granulate or tuberculate and has a pair of well-developed and upturned urogomphi, often with a deep pit or groove in between. The legs are 5-segmented and well-developed, and each claw bears two stiff setae. They occur in a wide variety of situations although UK species are mostly saproxylic, living under bark or among decaying wood and in fungi on a wide variety of deciduous and coniferous trees. More generally many are ground-living and occur among leaf-litter or under decaying plant material in arid areas, and those of Langelandia live in the soil and are blind, like the adults.

UK Species

Our two species of Synchita, and of Cicones, are widespread though very local and generally scarce across the south. Bitoma, Colydium and Aulonium trisulcum (Fourcroy, 1785) are locally common across much of England and Wales, while A. ruficorne (Olivier, 1790) is included on our list from an old record and has probably never been established. Pycnomerus fuliginosus Erichson, 1842 is a recently introduced Australian native; it was initially restricted to a few broadleaf woodland areas in the south but has spread rapidly and is now widespread and locally common. Langelandia anophthalma  Aubé, 1843 is a very rare species with only a few modern records from Kent, Surrey and Sussex. The saproxylic species will occasionally be encountered when searching under bark or sieving wood debris etc. and they regularly occur in extraction samples from such material, but the best way to record them is to search suitable habitats at night, they will often be found on the surface of bark or denuded wood, especially in the vicinity of fungus, and often among many other species e.g. mycetophagids, salpingids, ciids, tenebrionids and melandryids etc. etc. Bitoma crenata (Fabricius, 1775) is an exception as it will also be seen in numbers running around on the surface of fallen trunks and logs etc. during the day, and often exposed to bright sunshine.

Pycnomerus

fuliginosus

Orthocerus

clavicornis

Synchita

humeralis

Synchita

separanda

Cicones

undatus

Endophloeus

markovichianus

Langelandia

anophthalma

Cicones

variegatus

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