BYRRHIDAE Latreille, 1804
Although several are widespread and locally common these secretive beetles are generally difficult to find. Most species will be found by chance.
Around the World
This is a small family of about 40 genera and 500 species with an almost worldwide distribution but by far the greatest diversity is in northern temperate regions; more than 350 species in 24 genera occur in the Palaearctic region of which more than 45 are European and 13 occur in the U.K., by contrast about 35 occur in North America and about 20 are recorded from the Oriental region, 10 from tropical Africa and 5 are Neotropical. The Australasian region is relatively diverse with more than 70 species. The family is divided into 3 sub-families although the classification is far from settled, and the same applies to the placement of the family within the coleoptera. Amphicyrtinae LeConte, 1861 includes 2 species of the Nearctic genus Amphicyrta Eschscholtz in Germar, 1843. A further genus, Amphicyrtella Ponomarenko, 1990, is known from 2 mesozoic fossil species discovered in Russia. Several other genera have variously been included within the sub-family e.g. the monotypic Brachmys Fairmaire, 1885, 2 species of the Falkland Island endemic Chalciosphaerium Enderlein, 1912, and the Nearctic genera Lioligus Casey, 1912, variously classified as Simplocaria Stephens, 1829 (Byrrhinae), and Lioon Casey, 1912, which has been included in a separate sub-family, Liooninae, or in Amphicyrta, but is now included in Byrrhinae. Syncalyptinae Mulsant & Rey, 1869 is generally divided into 2 tribes although the generic limits are far from certain. The Microchaetini Paulus, 1973 includes 16 species in 2 genera and is restricted to the Australasian region; Microchaetes Hope, 1834 comprises 12 species from Australia, one of which, M. bryophilus (Lea, 1912) is endemic to Tasmania, while Papuamicrochaetes Puetz, 2002 includes 4 species restricted to New Guinea. The mostly Palaearctic Syncalyptini Mulsant & Rey, 1869 comprises 3 genera and about 75 species of which 2 genera and 12 species occur in central Europe, and 4 species in 2 genera extend to the U.K. Humerimopsis Fabbri, 2003 includes 2 species; H. giorgiofiorii Fabbri, 2003 from China, and H. planicorpis Fabbri, 2003 from Nepal. Chaetophora Kirby, 1823 (which is also the latin name for a genus of green algae) includes about a dozen species and is very widely distributed; 4 are Palaearctic, of which 2 occur Europe; C. minuta (Reitter, 1884) is very local in southern parts while C. spinosa (Rossi, 1794) occurs throughout including the U.K. and has also become established in Canada
POLYPHAGA Emery, 1886
BYRRHOIDEA Latreille, 1804
and the north-eastern United States, several species occur in Africa and one, C. monnei (Reichardt, 1975), occurs in Uruguay. Curimopsis Ganglbauer, 1902 is the largest group within the subfamily and is usually divided into 2 subgenera: Atlantopsis Franz, 1967 includes about 10 species from Madeira and The Canary Islands. Curimopsis s.str. Includes >60 Palaearctic species, with the greatest diversity in Asia and several are restricted to Japan, 11 occur in central Europe of which 3 extend into the U.K. Five species occur in the Nearctic region including the quaintly-named C. moosilauke Johnson, 1986 from Alaska. Many species of Curimopsis were formerly included within Chaetophora, and the Californian Curimopsis cooperi (Johnson, 1982) is sometimes classified as the only species of the genus Sierraclava Johnson, 1982.
The remaining species are included in the Byrrhinae Latreille, 1804, by far the largest group of byrrhids and with the widest diversity in Asia; 21 genera and > 280 species occur in the Palaearctic region, of which only 34 species of 9 genera occur in Europe. The group is variously classified into tribes, the largest of which is the Byrrhini Latrielle, 1804. Several genera within this tribe have an almost Holarctic distribution e.g. Porcinolus Mulsant & Rey, 1869 includes one Palaearctic and one Nearctic species, and Cytilus Erichson, 1846 includes 3 Palaearctic and 2 Nearctic species. The 2 species of Arctobyrrhus Munster, 1902 are Nearctic while Curimus Erichson, 1846 is Palaearctic with 6 of its 15 species occurring in Europe. The large genus Byrrhus Linnaeus, 1767 comprises about 10 Nearctic and 110 Palaearctic species of which 12 occur in central Europe; it is variously divided into subgenera: Sinobyrrhus Fabbri, 2000 includes 2 species from China, Seminolus Mulsant & Rey, 1869 includes 10 European species, Byrrhocaulus Fairmaire, 1901 includes several species from India and China, the monotypic Byrrhinus Pic, 1922 is Neotropical (Brazil), and both Aeneobyrrhus Putz, 1998 and Asiatobyrrhus Paulus, 1971 are Asian, Rotundobyrrhus Fabbri, 2000 includes 5 eastern-Asian species, Pseudobyrrhus Fiori, 1952 includes 7 Palaearctic species, and Ornatobyrrhus Fabbri, 2000 includes a single species from China; Byrrhus s.str. is more widely distributed with about 45 Palaearctic species of which 5 occur in central Europe, several Nearctic species and one in North Africa. The Exomellini Casey, 1914 includes the single genus Exomella Casey, 1914, represented in Russia and the Nearctic region. Morychini El Moursey, 1961 includes about 20 species of Byrrochomus Fabbri, 2003 from China, the monotypic Sinorychomus Fabbri, 2003 and Morphobyrrhulus Putz, 2007 also occur in China while about 20 species of Chlorobyrrhulus Fabbri, 2002 occur in Asia and Canada. The Holarctic genus Morychus Erichson, 1846 includes 2 Nearctic and 11 Palaearctic species of which 1 occurs in Europe, including the U.K. Pedilophorini Casey, 1912 includes the Neotropical Carpathobyrrhulus Ganglbauer, 1902, the European (mostly Spanish) Chrysobyrrhulus Reitter, 1911, the Japanese Lamprobyrrhulus Ganglbauer, 1902 and the more extensive Pedilophorus Steffahny, 1843 with 14 Palaearctic species but also others from New Zealand and Tasmania. The Simplocariini Mulsant & Rey, 1869 includes about 20 species of Chrysosimplocaria Paulus, 1982 and 10 species of Himalayoligus Fabbri, 2002 from Nepal, 6 species of Horiella Tazikawa, 1983 (sometimes considered a subgenus of Simplocaria) from Japan, the monotypic Shanna Putz, 2007 from China and about 12 species of the western European (mostly Spanish) Trichobyrrhulus Ganglbauer, 1902. The genus Simplocaria Stephens, 1829 includes about 55 Palaearctic (mostly eastern) species.
Several other groups remain ambiguous e.g. the New Zealand genus Synorthus Broun, 1910 and some fossil genera; the Cretaceous Fangshanella Huang Diying, 1910 and Mesobyrrhus Huang, 1997, and the Mesozoic Mesosimplocaria Ponomarenko in Ponomarenko & Ryvkun, 1990.
Byrrhids are small to medium-sized beetles, approximately 1-15mm in length and generally very convex dorsally, moderately so ventrally, and short- to elongate-oval in outline. Most are drab coloured; grey, brown or black although some are metallic bronze or green e.g. Lamprobyrrhulus nitidus (Schaller, 1783) or the common U.K. species Cytilus sericeus (Forster, 1771), and some have a distinct mottled pattern e.g. some Byrrhus species, while some are glabrous e.g. Carpathobyrrhulus the majority are to some extent pubescent or have a layer of dense recumbent setae or scale-like setae e.g. Morychus aeneus (Fabricius, 1775), and some have outstanding bristles or setae which may be simple, flattened, clavate or truncate e.g. Chaetophora spinosa (Rossi, 1794). The head is usually hypognathous so that in life it is generally only narrowly visible from above, although it is readily manipulated for setting, narrower than the pronotum though often as wide as the anterior margin, with the vertex and frons convex, the eyes weakly to moderately convex, and oval or sometimes weakly emarginate behind the antennal insertions; in life they are often hidden under the pronotum. The eyes and antennae are placed laterally; the antennae are 11-segmented and often have a small but distinct scape, and vary from simply filiform e.g. Simplocaria, to gradually expanded e.g. Porcinolus, or clubbed e.g. Curimopsis .The clypeus is reduced to almost absent, the labrum articulated and usually emarginate, the maxillary palps 3-segmented, labial palps 2-segmented, with the terminal segment pyriform or, in Amphicyrta, securiform. Mandibles generally inconspicuous; variously toothed apically and deeply notched internally about the middle. The pronotum is convex, broadest at the base and narrowed to obsolete or rounded anterior angles, the posterior angles are generally acute and to some extent produced, lateral margins finely to strongly bordered and the basal margin sinuate, often strongly so, and sometimes finely crenulate. Prosternal process well-developed; broadly rounded to acute, truncate or T-shaped apically, the pro-coxae are transverse with the cavities open posteriorly. The mesosternum is short and deeply recessed to receive the prosternal process; the meso-coxae are only slightly transverse, globular to flat and usually widely separated. The metasternum is broad and long with a distinct longitudinal suture and often only indistinctly divided from the mesosternum and generally deeply emarginate around the meso-coxae. The meta-coxae are widely transverse, almost reaching the elytral epipleura, and nearly touching at the centre. The scutellum is very small, sometimes hardly visible, and triangular to oval. Elytra completely covering the abdomen, convex and continuously or separately rounded apically and with variously developed epipleura which are sometimes complete to the apex. Explanate margin, if present, narrow and only present towards the apex, the surface varies from glabrous to completely and densely pubescent, in either case there may also be modified setae, scales or bristles, smooth to striate or with longitudinal impressions or series of punctures, the background punctation from fine and diffuse or sparse to strong and very dense. Abdomen with 5 ventrites; the first and second connate. Legs generally relatively long and slender and often flattened; trocanters triangular, the femora usually clavate and unadorned, tibiae slender to stout, and usually flattened, often characteristically curved, angled or toothed, and grooved externally to receive the tarsi, the surface often pubescent and with stiff setae or spines. Tarsi 5-5-5, (Byrrhinae), or 4-4-4, (Syncalyptinae), the third segment is sometimes lobed, and in some species all the tarsomeres are transverse and have pubescent pads ventrally. The claws are usually simple.
Byrrhids seem never to have been popular with coleopterists in the U.K.; the fauna is limited and some of these are very rare, and of the 13 species on our list 2 have been added in recent decades, Byrrhus arietinus Steffahny, 1842 in 1966 and Curimopsis nigrita (Palm, 1934) in 1978. In general their behaviour makes byrrhids difficult to find and because they are adapted to fully retract the appendages into grooves on the ventral surface of the body they are difficult to manipulate and set. Adults remain still and compact when disturbed, resembling seeds or small animal droppings, and so can be very difficult to find without-or even with-experience. On the other hand they may be found when sampling tussocks or litter from around the base of plants or moss, or from moss etc. on the surface of old logs. Both adults and larvae of most species are obligate moss-feeders but some have been recorded from lichens and liverworts, and some from higher plants e.g. species of Amphicyrta feed upon the leaves and stems of various herbaceous plants and deciduous shrubs and occasionally occur in large numbers among cultivated turf. Adults of bryophagous species graze on the surface while the larvae burrow into gametophyte layers and feed from the burrow entrance by extending the body to graze on nearby mosses. The larvae of some species of e.g. the Holarctic Cytilus or the Nearctic Arctobyrrhus are surface feeders and some have been recorded feeding upon clover, grasses and conifer seedlings. Adult byrrhids are generally crepuscular or nocturnal although some e.g. species of Byrrhus and Cytilus may be seen wandering paths or on bare soil among grass etc. in bright sun, most tend to remain within litter or among moss on the ground or on logs and stones but are readily seen by torchlight with careful searching. Several species occur generally in the U.K. e.g. Byrrhus pilula (Linnaeus, 1758) and Cytilus sericeus (Forster, 1771), but many will only be found in specific situations e.g. we have found Chaetophora spinosa (Rossi, 1794) in great abundance on calcareous grassland, Morychus aeneus (Fabricius, 1775) occurs near coastal streams, Porcinolus minimus (Fabricius, 1794) is a very rare heathland species, and Curimopsis maritima (Marsham, 1802) occurs on open calcareous or sandy soils near the coast. In the Nearctic zone byrrhids are most diverse and abundant in northern mountainous regions and around the Great Lakes, while some genera e.g. Lioon Casey, 1912, Lioligus Casey, 1912 and Listemus Casey, 1912 are restricted to northwest conifer forests. Sierraclava is restricted to California, and some species occur only in extensively wooded areas where numbers are known to increase dramatically after disturbance e.g logging or timber salvage that follows forest fires.