|Hydrobius fuscipes Leach, 1815|
|A common and often very common species throughout England and lowland Wales
and Scotland including the Western and Orkney Islands although there are no records from Shetland (NBN). The species
inhabits both fresh and brackish water (Hansen).
They are generally abundant in all suitable habitats along the Colne valley from Cowley to Watford. Usually an insect
of standing or stagnant water with at least some marginal vegetation but we have also recorded them from among vegetation
along the slower reaches of the river Gade on Common moor. They are active fliers and readily come to light and by this
means we have recorded them away from water e.g. in Whippendell wood. During 2007 and 2008 specimens were found through
jan and feb among samples of pondside vegetation, debris and reed litter from Cassiobury park and Radlett road. Adults
become active during the first warm days of march and may often be observed on wet, bare ground before the vegetation becomes lush.
They are soon abundant, being most easily observed by searching around the base of waterside plants but we almost always find them
among samples of aquatic vegetation, including Lemna, from most situations. Larvae are found from may and pupae and freshly
emerged adults from July (Hansen). Locally the adults are abundant during august and september, extending into october depending
6-8 mm. Upper surface black, weakly metallic especially foreparts (lateral margins often paler. Hansen) and entirely finely punctate. Appendages brown, tibiae darker, antennal club and tip of terminal segment of palpi black. Palpi about as long as antennae. Antennae 9 segmented with 3 segmented club, inserted under side of head in front of eyes. Eyes weakly convex. Head with an oblique series, sometimes obscure, of setiferous punctures beside eyes and 3 or 4, wider spaced, in front of eyes. Pronotum transverse and broadest at base, narrowed anteriorly and bordered laterally, very finely so on front margin. Front angles rounded and weakly protruding. With a group of large punctures laterally and another inside front angles which extends along front margin for a short distance then obliquely towards disc. Elytra entire and finely bordered, broadest about middle and with ten well impressed and punctate striae which are deepened towards apex. First stria interrupted in basal third at the level of the apex of a weak intercalary stria (sometimes missing, Hansen). Interstices flat, weakly convex near apex, some with a series of larger setiferous punctures, in our specimens these are on the odd numbered ones. Underside flat, finely shagreened and punctate with dense hydrofuge pubescence, obvious under a hand lens. Legs moderately long and slender. Tibiae with fine spines along outer sides; protibiae with a pair of small spines subapically on outer surface and two longer, curved spines one either side of tarsal insertions. Meso and meta tibiae with two large, unequal spines on inside at apex. Tarsi 5-5-5 first segment small so they may appear 4 segmented. Claws long and curved, appendiculate.
Two varieties are quoted in Hansen; var.rottenburgi Gerh., which is not on the Coleopterist checklist, has the elytral setiferous punctures situated within the striae rather than the interstices.Var. subrotundatus Steph. (synonym on checklist) is shorter, broader and has darker legs, elytral punctures normal.
Joy (p. 286) gives subrotundatus Steph. and also var.chalconatus (synonym on checklist) Steph. which is strongly 'greenish or bluish metallic'
Description from 4 Watford Specimens at X20