POLYPHAGA Emery, 1886
SCIRTOIDEA Fleming, 1821
SCIRTIDAE Fleming, 1821
Small and nondescript species, many of which are abundant during the summer in a variety of habitats, while others are more restricted. Identification can be very difficult, and often requires dissection.
Around the World
This is an interesting and probably unique family in the sense that they are the only known holometabolous insects whose larvae have multi-segmented antennae. They are otherwise rather nondescript, if distinctive, beetles; 1-15mm in length and generally drab; most are some shade of brown or grey although some are maculate or have pale borders and some tropical species are metallic. There are about 1400 described species and 50 genera included in 3 extant subfamilies and many more species await description. Two subfamilies are monogeneric; Nipponocyphoninae Lawrence & Yoshitomi, 2007 includes the monotypic Nipponocyphon Lawrence & Yoshitomi, 2007 with Nipponocyphon nakanei Lawrence & Yoshitomi, 2007 from Japan, adults of which have the typical appearance of the family although they are more densely pubescent than usual, and Stenocyphoninae Lawrence & Yoshitomi, 2007 which was known only from a series of specimens of Stenocyphon sasaji Lawrence, 2002 from flight interception traps in Nothofagus forests in Chile until the discovery of a further species, S. neozealandicus Ruta, Thorpe & Yoshitomi, 2011, from New Zealand. This last subfamily is a primitive group with features atypical of the family as a whole; 4.5-6.0mm, parallel-sided and very elongate with long appendages, tibiae that lack longitudinal carinae, long meso- and (especially) meta-tibial spurs, a distinct frontoclypeal suture, bidentate mandibles and lacina with an apical hook, and the females have a strongly sclerotized and blade-like ovipositor. With both groups the inclusion within the family is not absolutely certain. The vast majority are therefore classified within the scirtinae Fleming, 1821 but so far there is no suprageneric organization. The family is represented in all zoogeographical zones but is most diverse in tropical and southern temperate regions; Australia and New Zealand are particularly rich e.g. the Australian fauna includes about 225 species in 21 genera whereas about 50 species in 12 genera occur in North America. The European fauna includes about 100 species of which 25 occur in Germany, and the U.K. fauna by comparison is relatively rich with 20 species in 8 genera. By far the largest genus is Cyphon Paykull, 1799 with >300 species (in the broad sense), a cosmopolitan group with most species recorded from the eastern Palaearctic and southeast Asian
regions, the genus includes species variously classified in other genera e.g. C. brevicollis (LeConte, 1866), formerly Helodes Du Val, 1861, and some Nearctic species e.g. C. americanus Pic, 1913, C. neopadi Klausnitzer, 1976 etc. in Contacyphon Des Gozis, 1886. The genus, as with the family generally, includes many island endemics e.g. C. hamatus Klausnitzer, 1977 and C. venustus Klausnitzer, 1977 from Madagascar, and C. pigrams Klausnitzer, 1980 and C. pilumnus Klausnitzer, 1908 from Sumatra. The genus is only poorly represented in the Neotropical region. An example of an island endemic genus is Memorocyphon Pic, 1918, from Madagascar. The large genus Elodes Latreille, 1796 formerly included >160 mostly Palaearctic, Asian and Australian species but several have now been classified into Odeles Klausnitzer, 2004. Hydrocyphon Redtenbacher, 1858 includes >100 species from the Holarctic, Southeast Asian and African regions, and Microcara Thomson, 1859, with about 20 species, has a similar distribution. Prionocyphon Redtenbacher, 1858, with >40 species, is Holarctic, Southeast Asian and Australian. Sacodes LeConte, 1853, with about 30 species, occurs throughout Asia and Australia. The large and distinctive genus Scirtes Illiger, 1808 is Holarctic and Australian, extending south into east Africa and Central America. Many genera have a more restricted distribution e.g. Herthania Klausnitzer, 2006, with 8 species formerly included in Cyphon and Helodes is Holarctic and restricted to the northern hemisphere. Macrocyphon Pic, 1918 includes 7 species from Asia and Australia, while Pseudomicrocara includes >50 species, most of which are Australian but some occur in the Neotropics. Macrohelodes Blackburn, 1892, with 20 species, and Paneveronatus Armstrong, 1953, with 4 species, occur only in Australia, while Veronatus Sharp, 1878 includes about 20 species from New Zealand. The monotypic Sarabandus Leech, 1955 is Nearctic, while the 2 species of Prionoscirtes Champion, 1886 are Neotropical. Ora Clark, 1865, with 15 species, occurs throughout the tropics but is mostly Neotropical and a few extend into The United States. Many more species from all regions, especially southern subtropical areas, await description. The family is rich in fossil species, especially from Baltic amber, and some of these form distinct groups e.g. the Asian Mesozoic Mesernobius anawrahtai (Engel, 2010) constitutes the only member of the subfamily Mesernobiinae Engel, 2010.
Adult Scirtids are mostly soft-bodied, elongate and flattened although several genera e.g. Scirtes and Ora include some rounded and convex, almost globular species. Some are continuous in outline e.g. Macrohelodes Blackburn, 1892 (Australia) and Amplectopus Sharp, 1886 (New Zealand), but most are constricted between the pronotum and the elytra e.g. Elodes and Microcara. The New Zealand genus Veronatus Sharp, 1878 is atypical; members are very elongate with several longitudinal carinae and various depressions to each elytron, and a cryptic silky appearance due to the pubescence which is arranged in patches lying in different directions. Most Scirtids are pubescent and some are very densely so e.g. Nipponocyphon, the pubescence is often doubled but the dorsal surface generally lacks any discreet longer sensory setae, some genera e.g. Cyphotelus Sharp, 1878 and Macrohelodes are virtually glabrous. The head is naturally declined, although easily raised forward for setting, and sometimes almost completely concealed under the pronotum; the temples are well-developed although usually concealed; in some genera e.g. Stenocyphon and Cyphotelus they are long and obvious beyond the pronotum. The eyes are entire or only very weakly emarginate anteriorly, flat to very convex and lacking setae. A transverse occipital ridge is sometimes present and, with the exception of Stenocyphon, all species lack a distinct frontoclypeal suture, the labrum is free, transverse and truncate to weakly emarginate although occasionally strongly so e.g. in Byrrhopsis Champion, 1913, Atopida White, 1846 and Cyphanus Sharp, 1878. All have paired lateroventral subgenal ridges which line up against the outer edges of the pro-coxae when the beetle is at rest. The mandibles are short, broad and rounded to a sharp point, although bidentate in e.g. Stenocyphon and Amplectopus, and variously toothed internally. The apical segment of the labial and maxillary palps is elongate- cylindrical to short and conical. Antennae 11-segmented and generally filiform although sometimes serrate, never clubbed, and placed on the front of the head where the insertions are visible from above, sometimes they are placed in well-defined depressions, and the separation varies from narrow to very wide. Ventral antennal grooves vary from strongly depressed to absent. The pronotum is generally transverse and convex, often widely explanate laterally, and with the sides straight to strongly rounded, broadest from the base to the middle and usually narrowed anteriorly; the apical and basal angles generally rounded, sometimes contributing to a continuous curve anteriorly and often bluntly acute posteriorly, the basal margin varies from straight to widely and strongly sinuate. A lateral border is usually complete and visible from above. The surface is generally smooth; in some there are paired basal fovea but never longitudinal impressions, the punctation varies from very fine and sparse to rather strong and dense, and the pubescence from recumbent to semi-erect. Prosternum narrow, and sometimes very much so, in front of narrowly separated and transverse coxal cavities which are open laterally, the process extending back and sometimes overlapping the mesoventrite, usually strongly constricted between the coxae and apically expanded to a rounded or widely truncate apex, flat or concave to strongly convex and projecting above the coxae which usually project above the level of the prosternum. Pro-trocantins generally narrow and visible from below, in Stenocyphon expanded and quadrate or nearly so. Scutellum usually large and obvious, triangular to rounded. Meso-coxae close together or touching, round to strongly transverse and not, or only very weakly, oblique, not projecting above the mesosternum, the cavities open laterally. Meta-coxae close together or touching, transverse and extending laterally to the elytral epipleura, posteriorly expanded into plates which are excavated to receive the femora, these plates are generally complete although sometimes weaker laterally and sometimes reduced e.g. in Scirtes, Ora, Cyphotelus and Stenocyphon etc. Most species have well-developed hind wings and are strong fliers. The elytra completely cover the abdomen and are generally rounded apically, usually with distinct or well-developed shoulders and broad epipleura that continue to the apex although these are occasionally reduced or even absent. The surface is usually punctured and pubescent, often with double pubescence, and lacking striae although in Veronatus there are several complete longitudinal carinae, and in Nipponocyphon there are numerous obscurely developed longitudinal striae. In some species, especially of Cyphon, the cuticle is folded into several weakly developed longitudinal ridges. The females of many species possess depressions or folds towards the apex of the elytra which have been termed ‘excitations’ as they secrete substances thought to be pheromones used to stimulate males during mating. The abdomen had 5 ventrites; segments 1 and 2 are connate and the basal segment lacks postcoxal lines although in Amplectopus Sharp, 1886, a genus of otherwise typical Scirtids from New Zealand, segments 1-3 are connate and there are distinct postcoxal lines. Most Scirtids have thin legs of moderate length; the femoral base is separate from the coxa and the femoral-trocanter joint is strongly oblique. In some the hind femora are rather well developed e.g. some Elodes, and in some e.g. Scirtes and Ora they are large and thickened, an adaptation for jumping as in alticine Chrysomelids, which has earned them the common name of marsh flea beetles. The tibiae vary from glabrous to densely pubescent and the outer margins have 2 longitudinal carinae which often bear series of stiff setae or spines. There are 2 tibial spurs which are generally short and equal or subequal but in some genera e.g. Stenocyphon, Ora and Scirtes, they are long and unequal. The tarsi are 5-segmentes, usually with the fourth segment bilobed or at least expanded although others may also be expanded, otherwise the segments are quadrate to weakly elongate, Scirtes and some others are unusual in having the basal metatarsomere long and thin. Exceptionally e.g. in Amplectopus the tarsi are short and broad.
The majority of Scirtid larvae are small, <5mm, when fully grown but they are distinctive and will soon be recognized when dealing with extractions of marginal vegetation samples. Those of Nipponocyphon and Stenocyphon however are unknown. Most are campodeiform although members some genera e.g. Odeles are broad and flattened, superficially resembling small woodlice. All are strongly sclerotized above and below and the head is prognathous and smaller than the thoracic segments. All have multi-segmented antennae; between 5 and 20 segments, and the labrum is separated from the head by a distinct and complete transverse suture, the maxillary palps are 4-segmented and the labial palps 2-segmented, and the mouthparts are specialized into a very complex filter feeding mechanism with comb-like maxillary hairs and hypopharyngeal armature, and the mandibles are ventrally tuberculate. They lack urogomphi and the abdominal spiracles are reduced and non-functional, the abdominal apex has a single pair of large spiracles and a series of anal papillae, all aquatic species breathe atmospheric air at the water surface. In general very little is known of Scirtid biology although in temperate regions most are thought to produce a single generation each year, and many have a brief season of occurrence as adults. Most species develop in aquatic habitats such as the margins of lakes, ponds and rivers or among reed litter etc. but many occur in smaller and ephemeral habitats such as puddles in woodland or on moorland, some have been known to penetrate deep underground e.g. Scirtid larvae have been found in groundwater 10 metres
Elodes minuta (Linnaeus, 1767) larvae
below the surface. Others develop among decaying vegetation in damp conditions e.g. marginal as well as in tree stumps or among roots where water accumulates; some species of Cyphon, Prionocyphon and Sacodes occur in large numbers in pine hollows. Most larvae are good swimmers and are agile in the water, and many are active among moss on rocks, gravel and other substrate and submerged branches, vegetation and litter. Some tropical species develop in water droplets on leaves, in bromeliads or in permanently wet soil. Specialized terrestrial larvae occur in several southern Hemisphere areas; Chile, Borneo, New Zealand and Australia; those from Chile are saproxylic, feeding among debris in cavities. A feature of terrestrial larvae is large Prosternal sclerites. All larvae so far studied are microphagous, filtering food particles such as algae, fungi, diatoms and organic matter from various substrates with their modified mouthparts. Many larvae go through multiple instars and up to 11 have been recorded.
Adult Scirtids are most abundant and diverse in wetland and marginal habitats where they may be swept in numbers, but many will be found in woodland and wooded parkland environments, and slow-moving water in woodland situations can be very productive. When accidentally swept onto the water surface most species can walk to nearby vegetation etc. and some species of Elodes have been observed to gyrate like whirligigs. Many species occur on the flowers of a wide range of plant families and have been observed feeding upon pollen. They are diurnal, short-lived and many have a short season; in temperate regions generally from late spring to early summer although some e.g. Scirtes, may be found on marginal vegetation throughout the summer. Several species are common in the U.K. and will soon be found by general sweeping in marginal environments.
Our 2 species of Scirtes are very distinctive; 2.5-3.5mm, convex and broadly oval with the hind femora greatly enlarged and the metatibial spurs and first metatarsal segment very long. Both occur among marginal vegetation. S. hemisphaericus (Linnaeus, 1758) is dark, almost black, with fine dark dorsal pubescence and fine and discreet elytral punctures. This species occurs locally and sometimes commonly throughout England and Wales and more sporadically through Scotland to the far north. S. orbiculatus (Panzer, 1793) is lighter, usually orange-brown, and has longer and paler pubescence. The elytral punctation is fine and very dense with the punctures joined by tiny transverse ridges. It is a rare species recorded from southeast England. Our other genera are more typical of the family, less rounded and convex and with the hind legs normally developed. Prionocyphon serricornis (Muller, P.W.J., 1821) at 2.5-4.8mm is unique in having serrate antennae. It is a local insect of southern England occurring in wooded situations where the larvae develop in wet rot holes, especially on Beech. In all our other species the antennae are simply filiform. Hydrocyphon deflexicollis (Muller, P.W.J., 1821) is a small dark species, 2-2.5mm, with a distinctive tear drop shape; the elytra are broadest in front of the middle and tapered to the apex. The third antennal segment is very small. It is a rare species occurring near fast-flowing streams and rivers, often associated with sallows. Our other species are all rather parallel in appearance and the four genera can be split into 2 groups according to general morphology; in Elodes and Odeles the basal metatarsomere is longer than the remaining segments combined, and the second antennomere is shorter than the third. In Microcara and Cyphon the basal metatarsomere is shorter than the rest of the tarsus, and the second antennomere is shorter, or only as long as, the third. Odeles marginata (Fabricius, 1798) is widespread and locally common in wetland environments throughout the U.K. including Orkney and Shetland. It is distinctively coloured with the head dark and the pronotum yellow with a dark disc. Our four species of Elodes are wetland insects with at least one, E. minuta (Linnaeus, 1767) being generally common throughout. The larvae develop in running water. Microcara includes the widespread and common wetland species M. testacea (Linnaeus, 1767); this is superficially similar in appearance to Cyphon but is larger; 4.5-5.5mm. Our 10 species of Cyphon are smaller <4.5mm and all of a characteristic appearance, only 2 species are distinctive; C coarctatus Paykull, 1799 and C. palustris Thomson, C.G., 1865 are larger than the others at 3.5-4.5mm and have three weak longitudinal ridges on the elytra. Identification of Cyphon species is very difficult and uncertain without dissection.