TETRATOMIDAE Billberg, 1820
Polypore Fungus Beetles
All species are nocturnal and associated with fungus in woodland habitats. Tetratoma fungorum is the most common but all are widespread across England and Wales.
This family is very difficult to define as many of the species are superficially very similar to those of several other Tenebrionoid families, more particularly the Melandryidae, Mycetophagidae, Scraptiidae and Tenebrionidae, and many have been widely placed among the superfamily e.g. Hallomenus axillaris (Illiger, 1807) was named Mordella piceus by Marsham in 1802. The family is still often referred to in a narrow sense i.e. to include only the subfamily Tetratominae, and as such only about 25 species of the single genus Tetratoma Fabricius, 1790, but by most recent definitions it includes 5 subfamilies, about 20 genera and about 150 species, although this classification, based upon adult and larval character sets, may well change following molecular and cladistic analysis. Although the overall form of the beetles varies widely e.g. compare the compact oval form of Tetratoma with the elongate and rather characteristic form of Hallomenus or the broad and flattened form of some Eustrophopsis, they soon become familiar; typically they are small to medium sized beetles with proportionally large eyes which are variously emarginate, 5-5-4 tarsi without lobed segments, exposed antennal insertions and a distinct prosternal process. Species occur in all biogeographical zones and diversity varies within the groups. Briefly the 5 subfamilies are characterized as follows:
Tetratominae Billberg, 1820. As currently understood this group includes 4 genera and about 25 species which, with the exception of the monotypic Californian genus Sphalma Horn, 1872, were all included as subgenera of Tetratoma, a system that still persists in many publications. Falsoxanthalia Pic, 1932 includes 2 species, one from China and the familiar, if very local and rare, European F. desmarestii (Latreille, 1807). Incolia Casey, 1900 includes 2 Nearctic species. The Holarctic Tetratoma is the largest genus with 20 species in 2 subgenera; Tetratoma s.str. includes 9 species and is represented in the U.K. by the widespread T. fungorum Fabricius, 1790, while Abstrulia Casey, 1900 includes 11 species including the UK species T. ancora Fabricius, 1790. All species are medium sized <9mm, elongate-oval and rather parallel-sided, very finely pubescent to almost glabrous, have randomly punctured elytra or at most 10 rows of punctures forming striae, and a loose and elongate 4-segmented antennal club.
POLYPHAGA Emery, 1886
TENEBRIONOIDEA Latreille, 1802
Hallomeninae Mulsant, 1856 has variously been included in the Melandryidae but is now considered to form a distinct and very characteristic subfamily of the Tetratomidae. They may be recognized by the following combination of characters: Antennae filiform to serrate, not clubbed or distinctly thickened, terminal maxillary palpomeres elongate and fusiform to almost cylindrical, eyes deeply emarginate but remote from the antennal insertions, tibial spurs short and prosternal process elongate. The subfamily includes 2 genera and 18 species. Hallomenus Panzer, 1794 is divided into 2 subgenera; Hallomenus s.str. includes 13 species and is Holarctic, extending south to Florida (H. puncticollis (Blatchley, 1917)) whereas Xeuxex Champion, 1889 includes 4 species and is also Holarctic. A single species, H. binotatus Quensel, 1790, occurs in the U.K. Mycetoma Dejean, 1834 is a Palaearctic genus of 4 or 5 species.
Penthinae Lacordaire, 1859 includes 12 species in 2 genera. They are broadly oval and large for the family, >9mm, all have the third antennomere at least as long as 4+5 combined and longer than 1+2. Species of Penthe Newman, 1838 have striate elytra (with more than 11 striae) while those of Cyanopenthe Nikitsky, 1998 are randomly punctured, and Penthe has filiform antennae while those of Cyanopenthe have an abrupt 4- or 5-segmented club. The 2 species of Cyanopenthe are Asian (India and Thailand). Penthe is Holarctic with most species in the Far East, and only 2 are Nearctic.
Piseninae Miyatake, 1960 includes 11 species in 3 genera. They are all small, <9mm, elongate and relatively narrow with an abrupt 3-segmented antennal club and elytra bearing less than 11 striae. The Chilean Notopisenus Nikitsky & Lawrence, 1992 is monotypic and the only genus to occur south of the Holarctic. Pisenus Casey, 1900 includes 7 species from eastern Asia (Japan, Korea and Taiwan) and the Nearctic (2 species). Tripyllia Reitter, 1898 includes one Nearctic and one or two western Palaearctic species.
Eustrophinae Gistel, 1856. This, the largest of the subfamilies, presents formidable difficulties in classification; it was formerly included in the Melandryidae but is now only partly retained in that family and partly transferred to the present one although in some works it is entirely included in the Tetratomidae. Included are 3 tribes, the Orchesiini Leconte, 1859, which includes 4 genera and about 90 species including the familiar Orchesia Latreille, 1807, is retained in the Melandryidae while the Holostrophini Nikitsky, 1998 and the Eustrophini Gistel, 1856 are transferred to the present family. Holostrophini includes 2 genera and is mostly eastern Palaearctic; of the 17 species of Holostrophus Horn, 1888 only one is Nearctic, and of the 4 species of Pseudholostrophus Nikitsky, 1983 2 are Nearctic and 2 are from China. Eustrophini includes 3 genera. The 3 species of Allopterus Broun, 1883 and 8 species of Ctenoplectron Redtenbacher, 1868 occur in Australia and New Zealand. Eustrophopsis Champion, 1889 includes about 55 species and is widespread in the New World, Eastern Asia and Africa and includes several Madagascan endemics. Members of the subfamily are elongate-oval and convex with distinct lateral ridges on the pronotum, and eyes, entire or emarginate, that reach the antennal insertions.
The species are generally saproxylic; adults may be found under bark in the vicinity of bracket fungi on a very wide range of both coniferous and broad-leaved trees but are most easily observed at night when they are active on the surface of the wood or on fruiting bodies, often in numbers. Most species are easily sampled as they move slowly and are easily beaten into a tray or net, many remain still for some time under torchlight but some, e.g. Hallomenus, may become very active when disturbed. Both Adults and larvae are thought to be fungivores, feeding and developing on the fruiting bodies of wood-rotting Hymenomycete fungi but more especially Polyporaceae and Tricholomataceae, adults feed on the surface while larvae burrow through the tissues.
All are small to medium sized beetles, 2-18mm (in some Penthe spp.), elongate to broadly oval, almost continuous, e.g. Eustrophus, to strongly discontinuous e.g. Penthe, in outline and drab coloured, brown to black or, rarely, brightly coloured and metallic e.g. Tetratoma, or with pale spots or patterns e.g. Tetratoma ancora Fabricius, 1790 or Holostrophus bifasciatus (Say, 1824). Penthe obliquata (Fabricius, 1801) is entirely black but for the large, bright-orange scutellum and terminal antennomere. Any pubescence is generally fine and recumbent but many are almost glabrous. Head generally in line with the body axis, often proportionally small, inserted into the thorax so that the temples are often hidden, and narrowed anteriorly. Vertex variously punctured and microsculptured or rugose, sometimes impressed (Penthe), eyes large, convex and variously emarginate, narrowly to widely separated. Frontoclypeal suture variously impressed and sometimes incomplete, labrum quadrate and generally concealing the short, curved and blunt mandibles, palps relatively long and prominent; maxillary palps 4-segmented with the basal segment tiny and the terminal segment often expanded, labial palps 3-segmented with the first segment tiny. Antennae inserted laterally in front of the eyes, the insertions generally visible from above, rarely concealed by narrowly expanded lateral genae, 11-segmented and filiform, weakly serrate or with a distinct 3 or 4 segmented club. Pronotum quadrate to transverse, broadest at the base and evenly narrowed to rounded anterior angles, or broadest at the middle and narrowed to obtuse anterior and posterior angles, much broader than the head and as broad as, or narrower than, the base of the elytra, rarely e.g. in Holostrophus, broader. Basal margin generally sinuate, often strongly so. Lateral margins bordered, generally smooth but sometimes crenulate or, rarely, distinctly angled and appearing toothed e.g. in Tetratoma tessellata Melsheimer, 1844, and sometimes explanate e.g. in Triphyllia Reitter, 1898. Surface evenly convex, often only weakly so, variously punctured and microsculptured and often with a pair of basal fovea. Prosternum short and broad in front of rounded to transverse-oval coxal cavities which are open posteriorly and open or closed internally. Prosternal process short and broad, continuing to the posterior margin of the coxae, pointed to rounded or truncate apically. Mesosternum generally short although longer in some genera e.g. Hallomenus, and often angled posteriorly to accommodate the anterior margin of the metasternum, metacoxal cavities transverse-oval although almost round in some species e.g. Triphyllia elongata (LeConte, 1875), and open internally. Metasternum broad and long, often flattened and longitudinally impressed medially, and extended between the mesocoxae to meet the mesosternum. Metacoxae widely transverse, extending almost to the elytral epipleura, contiguous to moderately widely separated e.g. in Synstropus. Scutellum visible, usually relatively large, triangular; straight or sinuate laterally and rounded to acute apically. Hind wings usually well-developed. Elytra entirely covering the abdomen and usually continuously rounded, sometimes separately so e.g. Hallomenus, and usually contiguous, rarely divergent towards the apex as in Hallomenus, shoulders evenly convex and not prominent, lateral margins evenly curved to almost parallel-sided, epipleura broad basally and narrowing to the middle, often absent in the apical half. Surface randomly and finely to strongly punctured, often with distinct striae complete to the apex or evanescent after the middle, in some Hallomenus with weak longitudinal costae, without a scutellary striole. In some groups without a trace of striae e.g. Tetratoma or Triphyllia. Microsculpture generally fine but sometimes strong or rugose. Abdomen with 5 visible ventrites, the basal two often connate. Legs generally long and slender, coxae flat to moderately projecting. Trocanters small and triangular, femora unmodified, without teeth or carinae, at most moderately broadened, tibiae slender and only weakly, if at all, broadened apically, mostly with distinct spurs on the inner apical angle. Tarsi 5-5-4, with all segments obvious and usually cylindrical, the basal meso- and metatarsomeres longer than the others, the protarsal segments equal or nearly so. Claws simple, paired and equal in length.
The larvae vary from 3-17mm when fully grown but most are <10mm. They are elongate and sub-cylindrical or weakly flattened and fusiform, parallel-sided or a little broader anteriorly. Most are white to creamy with the head and various sclerites darkened, and glabrous or with scattered erect setae. The abdomen is 10-segmented with the ninth segment generally simple, in Hallomenus with a single lateral asperity, and generally with 2 upturned and bifid urogomphi and a single tubercle at the base. Legs 5-segmented with a bisetose tarsulgulum.
A key to the British species can be found HERE.