Noterus clavicornis (De Geer, 1774)
Widely distributed throughout England and Wales including the Isle of Wight, Anglesey and Man, in the west country records are mostly coastal. In Scotland most records are from the southwest; Dumfries and Galloway and Ayr north to Glasgow and there is an older record from Fife (NBN). Balfour-Browne quotes two records from Ramsay (North Ebudes) and states that the two species (ie with N.crassicornis) are frequently found together. They are well known from brackish water and there are many coastal records. The species is generally common and may be abundant, adults are usually found among submerged and decaying vegetation in permanent water bodies, they swim well but spend much time crawling on aquatic vegetation, we have recorded them several times from samples of vegetation taken for burlese extraction. Included on our Watford list from specimens recorded at Radlett road in deep stagnant water bordering dense reed beds, a population has been observed at this locality each year between 2006 and 2008.

Adults overwinter below the water and an egg has been discovered in late May (Holmen, 1987) under a decaying Scirpus (Bulrush) leaf although this may or may not be typical. Young larvae have been recorded in late June and mature specimens in August, they mine among the roots of grasses, sedges and rushes eg Alisma (water plantains), Juncus (Rushes), Scirpus (Bulrush), Typha (reedmace) and Spargonium (Bur-reeds). In captivity they have been recorded feeding on dead insects and pieces of meat although this may not be typical of wild behaviour. Larvae obtain air for respiration by penetrating roots with the pointed tip of the abdomen and will not come to the surface unless forced to do so. Mature larvae construct a cocoon on a root from particles of debris and secretions, air from the root being used to fill the cocoon. Larvae, pupa and cocoon (after Balfour-Browne) are illustrated in Holmens work. Cocoons and young adults have been recorded in August, and Jackson (1973) records adults from March, April, June, September(Abundant) and October among Polygonum amphibium, Hipparis vulgaris (Mare's tal) and Scirpus lacustris (Bulrush) in shallow water at Kilcongutar Loch (Fife) between 1949 and 1955, the majority of specimens examined in this study lacked normal flight muscles.

Outline characteristic; boat shaped with elytra broadest in front of middle and continuous laterally with pronotum, head discontinuous with outline. Upper surface convex, lower surface only very weakly so. Colour varies from pale testaceous to dark olive brown, centre of pronotum generally darkened. Eyes round, not notched but gently sinuate behind antennal insertions, antennae inserted behind side of head. Surface of head shiny, microsculpture just visible and with a few fine punctures anteriorly. Front margin of clypeus emarginate, front margin of labrum straight. Antennae characteristic; in male the middle segments are dilated and five is about as long as six. Pronotum strongly convex, widest at base and with a fine impressed line running parallel to lateral and front margins, generally punctate to some extent behind front margin. Front angles produced, front and hind angles more or less perpendicular. Hind margin sinuate, produced at centre so covering scutellum. Microsculpture just visible at X10. Elytra convex anteriorly, becoming flattened towards apex, lateral margin sinuate and finely bordered. Surface shiny and very finely microsculptured, with large punctures more or less evenly distributed in apical third, anterior of this forming two or three indistinct rows which also contain a few very fine punctures. Legs dark brown. Front tibiae short and broad, sinuate on inner surface. Mid tibiae short and elongate-triangular, hind tibia longer and parallel sided. Mid and hind tibiae with a pair of long spines on inner side of apex. Front and middle tarsi dilated in male. Hind tarsi long and evenly tapering. Mid and hind tibiae and hind tarsi with long swimming hairs. Tarsi 5-5-5, each with two weakly curved and equal claws. Prosternum with a raised elongate ridge which extends from front margin to between the coxae, front margin produced to a small and sharp point in front of this ridge.

Description from 3 Watford specimens at X20

Holmen 1987 The Aquatic Adephaga of Fennoscandia and Denmark. Fauna Entomologica Scandinavacia Vol. 20 E.J.Brill, Leiden
Jackson, D.J. 1973 The influence of flight capacity on the distribution of aquatic Coleoptera in Fife and Kinross-shire.Ent. Gaz. 24:247-293

Male Antennae

Female Antennae

Male Foretibia

Male Midtibia