NOTERIDAE Thomson, C.G., 1860
Burrowing Water Beetles
Includes two widespread species, one of which (N. clavicornis) is generally abundant in most aquatic situations.
ADEPHAGA Clairville, 1806
NOTERUS Clairville, 1806
N. clavicornis (De Geer, 1774)
N. crassicornis (Müller, O.F., 1776)
Around the World
This small family of water beetles includes more than 260 species in about 16 genera and is almost cosmopolitan in distribution; it is most diverse in tropical regions and only poorly represented at higher latitudes e.g. 14 species of 6 genera occur in the United States and 6 species in 4 genera are Australian while only 2 species occur throughout central and northern Europe. Adults are superficially similar to dytiscids but here the ventral surface is flat and the hind coxae are raised above the metasternum. They differ from gyrinids in having the eyes entire (or missing altogether) and the middle and hind legs normally developed, and from the Hygrobiidae by the general habitus and in lacking a transverse suture on the metasternum. The family was formerly divided into 4 tribes but following recent revisions now includes 3 subfamilies:
The Notomicrinae Zimmermann, 1919, formerly a tribe of the Noterinae, includes at least 9 species of Notomicrus Sharp, 1882 which is classified into the single tribe Notomicrini Zimmermann, 1919. With the exception of the widespread Southeast Asian and Australian N. tenellus (Clarke, 1863) all species occur in Central and South America, with two extending into the United States. They are small beetles, <2mm, and typical of the family in appearance; elongate-oval and drab coloured, pale to dark brown and variously mottled or streaked. Some species are occasionally abundant and occur in large numbers at light.
Phreatodytinae Uéno, 1957 includes at least 7 species of Phreatodytes Uéno, 1957 within the single tribe Phreatodytini Uéno, 1957. According to some recent research this genus may belong within the Notomicrinae. The species are very atypical of the family being minute, relatively slender and lacking eyes. In outline they are elongate and discontinuous with the pronotum broadest in front of the middle and strongly sinuate before acute and sharp hind angles, the front angles are variously produced and the lateral margins of the pronotum and elytra bear long and stiff sensory setae which are generally well-developed e.g. in P. archaeicus Uéno, 1996 although lacking in P. mohrii Uéno, 1996. The antennae are filiform and the legs slender and relatively long. They are drab and rather flattened species with the dorsal surface finely and densely punctured. The genus is
endemic to Japan and all species are subterranean, living among interstitial water in aquifers and among gravel in riverbeds near estuaries. It is thought that all species are endangered due to extraction and abuse of natural water tables.
All other species are included in the Noterinae Thomson, C.G., 1860, which is divided into 3 tribes. The Neohydrocoptini Zalat, Saleh, Angus and Kaschef, 2000 includes about 30 species of the single genus Neohydrocoptus Sató, 1972. The distribution extends across Southeast Asia to Australia, Southern Asia and the Middle East but the majority occur in Africa with 2, N. bradys (Guignot, 1955) and N. placidus (Guignot, 1955), endemic to Madagascar. A single species, N. subfasciatus (Sharp, 1882) occurs in Australia (Queensland). The very widely distributed N. subvittulus (Motschulsky, 1859) occurs throughout Southeast Asia, China, Japan, India, Nepal and Pakistan west to Iraq, and there is a subspecies endemic to the Seychelles, N. s. seychellensis (Paderzani & Sanfilippo, 1978). The Pronoterini Nilsson, 2005 includes 3 species of the new world genus Pronoterus Sharp, 1882; one occurs in the United States and two are Neotropical, one from the Caribbean (Guadeloupe) and one from Argentina and Brazil.
The Noterini Thomson, C.G., 1860 includes more than 200 species in more than a dozen genera, it is dominated by several large genera but the limits of these and the placement of species is far from settled e.g. the genus Canthysellus Bacae & Toledo, 2015 was erected to accommodate Noterus buqueti Laporte, 1835 which was found to be obviously not a species of Noterus. Recent research is also adding further groups to the tribe e.g. Prionohydrus Gomez & Miller, 2013 includes 3 new Neotropical species. The largest genus is Canthydrus Sharp, 1882 with about 70 species distributed in warmer region throughout the world. Two subgenera are recognized of which Canthydrus s.str. includes most of the species and is distributed throughout much of the old world. It is represented in Australia by 3 species; 2 are endemic while C. bakeri Peschet, 1921 also occurs in the Oriental region. With 38 species Africa is the most diverse region, and of these only 2 are more widespread, also occurring in the Palaearctic e.g. C. diophthalmus (Reiche & Saulcy, 1855); many of these are widespread, mostly across near-equatorial areas, but some are more localized e.g. C. flavosignatus Regimbart, 1903 occurs in Zaire and Madagascar, and C. guttula (Aubé, 1838) occurs in Madagascar and the Mascarene Islands (east of Madagascar). Two species, C. concolor Sharp, 1882 and C. andobonensis Guignot, 1960 are Madagascan endemics. Nine species occur only in the Oriental region and another 6 are more widespread, occurring across both Oriental and Palaearctic regions. Four species occur only in the Palaearctic. Again the distributions vary widely e.g. C. flavus (Motschulsky, 1855) is a very widespread Oriental species while C. arabicus Sharp, 1882 is endemic to Saudi Arabia. The subgenus Liocanthydrus Guignot, 1957 includes 4 Neotropical species; 3 from Brazil and one from French Guiana.
The large genus Hydrocanthus Say, 1823 includes more than 50 species in 2 subgenera. Hydrocanthus s.str. includes about 20 new world species with the greatest diversity in Central and South America but some extend into the United States e.g. H. iricolor Say, 1823 is widespread across North America and into Canada (Ontario and Quebec). The subgenus Sternocanthus Guignot, 1948 is old world with almost all of the 30 or so species occurring in Africa; 2 occur in Australia while one, H. indicus Wehncke, 1876 is a widespread Oriental and eastern Palaearctic species. A few of the African species are widespread e.g. H. wittei Gschwendtner, 1930 but most are localized and at least 3, H. delphinus Guignot, 1942, H. fabiennae Bameul, 1994 and H. gracilis Kolbe, H. J., 1883 are endemic to Madagascar.
In general appearance adult noterids superficially resemble dytiscids and in detail share many similar morphological structures e.g. the smooth body outline which forms a streamlined shape without protuberances or setae (except in the subterranean Phreatodytes), mostly filiform antennae and the metacoxal articulation; the mode of swimming is similar, using the hind legs together to push through the water, unlike Hygrobia which uses all the legs to ‘paddle’ with alternate movements. The structure of the hind coxae is unique to noterids, having the underside raised above the metasternum and flattened. In some species the antennae are dimorphic, having various segments expanded in the male. Noterids are small to medium sized beetles, <1mm to about 8mm and generally elongate-oval although some species are much broader e.g. the New World genus Suphis. The colouration is generally drab, from pale to dark brown and some are variously mottled or streaked lighter or darker. The head is transverse and only weakly protruding, generally widely rounded anteriorly and with weakly convex and entire eyes which follow the contour and touch, or nearly touch, the anterior margin of the pronotum. The surface is smoothly convex, finely punctured and microsculptured and lacks distinct sutures. The labrum is widely transverse, the mandibles are bifid and the terminal segment of all palps is elongate and much longer than the basal segments. The antennae are 11-segmented, glabrous and filiform. Pronotum broadest at the base and smoothly narrowed to protruding anterior angles, lateral margins bordered, sometimes very finely so, and the basal margin is sinuate and produced medially, covering the scutellum. The surface is smoothly convex and usually very finely punctured and microsculptured, and there are sometimes scattered larger punctures, especially towards the margins. Prosternal process well-developed; widened posteriorly and projecting over the mesosternum and touching the metasternum. The notopleural sutures are deeply impressed, the pro-coxae oval and both the proepisternum and the hypomeron are broad. The mesocoxal cavities are open laterally, the metacoxae large and transverse, extending laterally to meet the elytral epipleura, and developed medially into longitudinal raised plates which partly or completely cover the trocanters and the femora. The metasternum is produced backwards medially to meet the mesocoxae. Front and middle legs short and robust with broad tibiae which are modified for burrowing and crawling. The front tibiae lack an antenna cleaning notch. The hind legs are longer and modified for swimming with long hairs to the tibiae and tarsi. Basal abdominal ventrite covered by the hind coxae, ventrites 2 and 3 connate and 4-6 free. Tarsi 5-5-5 and generally not sexually dimorphic. Elytra completely covering the abdomen, widest at, or close to, the base and bordered laterally. The elytral surface is glabrous, finely microsculptured and often has scattered larger punctures which may form indistinct rows but never striae.
Noterid larvae are small, mostly <5mm when fully grown. Those that are known are compact and fusiform, elongate and almost parallel-sided, and have very small legs which are often concealed from above and which terminate in two claws. The body lacks gill filaments or micro-tracheal gills and the urogomphi are rudimentary and sometimes not visible. The abdomen has eight visible segments; the terminal segment is conical and usually produced over a rudimentary ninth segment which forms a tapered process (siphon) bearing apical spiracles but lacking ventral gills. The head is transverse or quadrate and at least partly retracted into the prothorax, the antennae are short; less than half the head width, and four segmented, the labrum is separated from the head capsule by a distinct suture, and the mandibles are stout with a well-developed retinaculum (internal tooth) but lack a suctorial mesal groove. Some larvae are noted for the habit of burrowing among substrates but many live among submerged vegetation, much like dytiscid larvae. They were previously thought to feed on detritus but those kept in captivity e.g. species of Noterus, Canthydrus or Hydrocanthus, have been found to be carnivores, feeding upon small insects, worms and carrion. Those larvae examined do not surface to replenish their air-supply, although they will do so if forced to, but respire by tapping into aquatic plant roots and stems with the pointed tip of the eighth abdominal segment. All larvae examined produce a cocoon of glandular secretions and debris which is attached to aquatic stems or roots among substrate from which it is filled with air. Noterid beetles typically occur around the margins of shallow water bodies and marshes or in temporary or permanent ponds but some also occur in slow-moving water. Most adults prefer stagnant conditions with plenty of submerged vegetation and filamentous algae where they spend most of their time among the roots of marginal of floating plants or buried in the substrate. Some species occur in a range of conditions from fresh to brackish while some are restricted to one or the other; some Australian species are known to inhabit brackish water in the burrows of land crabs. They are known to be carnivores and will capture prey while swimming although in general they are only weak swimmers. Adults will often occur in samples swept from among aquatic vegetation and most are strong fliers, sometimes occurring in numbers at light.
The family is represented in the UK by two species of Noterus; N. clavicornis (DeGeer, 1774) and N. crassicornis (Muller, O.F., 1776). The genus is very typical of the Noterini, the species being small, 3.5-5.5mm, somewhat shiny-drab brown, oval and dorsally convex. The oval shape which is broadest before the middle soon becomes recognizable. The entire dorsal surface is finely microsculptured. Head relatively small with weakly convex eyes that follow the outline, a short, transverse labrum and bifid mandibles.
Antennae 11-segmented with some middle segments enlarged, especially in the males. Pronotum broadest at the base and evenly narrowed to the anterior margin which is bordered by a series of punctures which may be joined by a transverse furrow, hind margin sinuate and produced over the scutellum. Elytra bordered laterally, the surface with scattered large punctures which tend to form irregular rows in places-but not striae-and are more numerous towards the apex. The prosternal process is widened apically and rounded or angled; for our species its form is diagnostic, with a ridge from the anterior margin to the median constriction in clavicornis, smoothly arched in crassicornis. Hind coxae produced into plates posteriorly which overlap the second and third abdominal sternites. The front and middle legs are short with broad tibiae that are modified for burrowing and crawling. Males have the front legs variously developed, usually the tibiae and tarsal segments are dilated and the basal tarsal segments have sucker hairs beneath. All tarsi are 5-segmented.
There has been some confusion in the past regarding the names of our U.K. species; N. clavicornis having been known as N. capricornis while N. crassicornis has been known as N. clavicornis. As things stand the larger species is N. clavicornis and the smaller is N. crassicornis. They are readily separated:
The larger Noterus
Larger species, 4.0-5.0mm. Larger punctures on the elytra arranged randomly. Prosternal process with a distinct ridge in the anterior half. Raised part of the metacoxae finely and densely punctured. Male antennomeres 5 and 6 equal in length. Common and widespread throughout England and Wales, much less so in Scotland. By far the most frequently recorded species.
The smaller Noterus
Smaller species, 3.5-4.0mm. Larger punctures on the elytra arranged in 3 loose longitudinal rows. Prosternal process regularly convex in females; flattened in males. Raised part of the metacoxae finely and sparsely punctured. Male antennomere 5 about twice as long as 6. Local in Southern England and Wales north to Yorkshire, more local and scarce further north.