Stenus fornicatus Stephens, 1833
A widespread but very local species of southern England west to north Somerset and north to the west midlands including east Anglia, most records are from the southeast (Hyman and Parsons). Generally found among vegetation near the margins of fresh water, the species is active in bright sunshine when they may be swept from the stems of sedges and rushes, often in company with other 'climbing' species e.g. S.juno or S.solutus. During cold weather they reside in low vegetation or under debris. We have a single winter record from February 2007, and during April 2007 several adults were found under the bark of a fully submerged Salix log in Cassiobury park. From April onwards they occasionally occur in samples swept from areas of sedges etc. bordering the old watercress beds in Cassiobury park nature reserve, to date (May 2008) only single specimens have been recorded. They seem to avoid dry situations; none were recorded from samples of vegetation taken during the summer and autumn of 2006 when the nature reserve ponds were completely dry by August, during 2007 the area remained waterlogged through the summer and (a few) specimens were present in samples. Our latest 2007 record was from 22/10 and so, along with the data from Hyman and Parsons, it seems the adults occur year round. Despite much sampling in apparently suitable local habitats e.g Radlett road ponds and the river Gade along Common moor we have yet to find the species outside the Cassiobury park area.

With a little experience the species can be identified with a 10X lens in the field; the broad elytra and tapering abdomen are distinctive.

2.5mm. or so, small for a Stenus. Entire upper surface shining black with sparse and very fine white pubescence. Antennae dark brown, club black. Palpi dark with pale basal segment. Head a little wider than pronotum, coarsely and densely punctate , about the same as on pronotum. Pronotum quadrate or nearly so, broadest at middle and without lateral borders. Elytra much wider than pronotum, about 3:2, and distinctly transverse, about 3:2.5, broadest behind middle. Punctures on disc larger and less dense than those on pronotum, finely bordered throughout including suture. Abdomen strongly tapering, first four (visible) segments strongly punctate along base, next two segments finely punctate and appearing dull due to microsculpture. Basal segment with a fine lateral border. Legs dark with base of tibiae orange or yellow and tarsi a little lighter, almost brown. Fourth tarsal segment strongly bilobed, contrasting with third. Claws proportionally large.

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