Stenus solutus (Erichson, 1840)

A local south eastern species with records west to Bristol and north to south Yorkshire, Around Watford found only along the margins of the river Gade from Common moor through to Cassiobury park although apparently suitable habitats occur throughout the area. Occurs from May through to November (so far as recorded) on wet mud and among dense riverside vegetation and needs to be looked for carefully, during hot sun they climb plant stems and so can be swept. Usually alongside marsh carabids and other Stenus species including the closely similar S. cicindeloides (Sch.). Occasionally found (01/05/07, Common moor) on open wet mud away from its riparian habitat, again on this occasion among many carabids (Bembidion dentelllum (Thunberg)) and a large population of Heterocerus fenestratus (Thunberg).

5.0-6.5mm. Base of antennae yellow, usually darkened from 5th segment. Head, thorax and elytra entirely punctate, without any smooth areas or impressions to pronotum, with sparse recumbent white pubescence. Abdomen parallel sided for basal 2 thirds, without raised border except on first and base of second visible segments. Basal segments rugose basally, apical segments finely punctate throughout. Legs darkened as figured, 4th tarsal segment strongly bilobed, much wider than third which is simple. Elytra as long as broad, not (or only very slightly) broader than head (cf S.cicindeloides). We have included the measurements (arbitrary units) for the specimen pictured for guidance as it is definitely S.solutus. The adaegus is figured as it is very different from S.cicindeloides and, for that matter, from all other British Stenus; parameres dilated and obliquely truncate apically, shorter than adaegus. Adaegus characteristically narrowed to apex.

In Tottenham keys out with S.cicindeloides, and the differences are subtle, especially the puncturation and shine. Comparing head and elytral widths is a good clue to the species (and essential for females). While examining a (supposed) series of S.cicindeloides and being unconvinced of the measurements we dissected several of the most slender looking specimens and immediately found solutus. Even after identifying both species the differences in puncturation and shine are not that obvious.

Elytral Length    1.05mm   (21 units)
Elytral Width     1.05mm   (21 units)
Head Width       1.00mm   (20 units)

It should be noted that measuring from the screen or from a printout may give different results as the specimen is not mounted flat. It needs to be oriented to the graticle to get meaningful results.

Description from 2 Watford specimens at X20