Bagous collignensis (Herbst, 1797)
Widespread but sporadic and very local throughout Central and Western Europe but generally very rare in the south, this species extends north into the UK, Denmark and southern Sweden and Finland, it has also been recorded from Asia Minor, northern Kazakhstan and Siberia and so the distribution remains poorly understood. In the UK it is very local and rare; there are scattered records from southern England, most of which are coastal or nearly so, and Northern Ireland and a few older records from Cumberland and Kintyre. The species is usually associated with well-vegetated margins of ponds, ditches and slow-moving rivers although we have sieved a single specimen from deep reed-litter near Watford in Hertfordshire and so it is worth working any marginal site for the species. The usual host plants are various Water milfoils (Myriophyllum L.), especially Spiked Water-milfoil (M. spicatum L.); adults are often observed on Marsh horsetail (Equisetum limosum L.) and occasionally on other marginal plants such as Purple Loosestrife (Lythrum salicaria L.). Little is known of the biology but it is likely that larvae overwinter as near fully-grown examples have been found in the spring, these have been found in stems, where pupation is thought to occur in the spring, and also in damp soil during the winter. Teneral adults have been recorded from April and adults generally persist into December although it is not known whether these overwinter. Adults are diurnal, they spend most of their time concealed among litter or matted algae but in warm weather they walk on wet soil, often exposed to the sun, and they sometimes climb stems.
2.2-3.2 mm. Elongate and convex, glabrous or nearly so, body dull brown with paler stripes to the pronotum and variable mottling to the elytra; in fresh specimens often with a patch on the third interstice that may extend onto the fourth or fifth interstice, antennae darkened towards the apex, legs usually with dark femora and pale tibiae and tarsi. Entire dorsal surface with dense and smooth granules, between which is a dry and shiny secretion which resembles dried slime or mud. Head broadest across weakly convex eyes which usually meet the anterior pronotal margin, vertex and frons flattened and without obvious depressions or sculpture. Rostrum short; shorter than the pronotum, broad and widened apically, the scrobes glabrous and narrowly visible from above towards the apex, in males shorter and more curved.
Antennal scape about as long as the distance between the anterior margin of the eyes, narrow at the base and broadened from the middle, funicular segments short and transverse, the club compact, elongate and pointed, and finely pubescent throughout.. Pronotum transverse, broadest in front of the middle and slightly narrowed to perpendicular or slightly obtuse posterior angles, constricted across the apical quarter and with lateral post-ocular lobes that are visible from above. Pronotal surface smoothly convex or with a fine longitudinal median groove which may be interrupted at the middle. Scutellum tiny and hardly visible. Elytra elongate and smoothly narrowed from widely-rounded shoulders to a continuous apical margin, striae narrow, finely punctured and, at least for the most part, visible among the granular surface, interstices flat, at most only weakly convex towards apex, without scales but with scattered short pale setae. Femora unarmed. Tibiae characteristic; strongly curved internally before the apex and produced into a sharp inward-pointing spine. Tarsi 5-segmented, although often appearing 4-segmented due to the diminutive forth segment, and slender, without broadly lobed segments. Basal segment of hind tarsi elongate and the second segment quadrate or very slightly transverse. Claws free and not toothed at the base.
Identification of this species can be difficult as it is very closely similar to B. longitarsus Thomson, C.G., 1868, with which it sometimes occurs, at least on the continent. There are differences in the rostrum, antennae, pronotum and elytra but these are slight, they become easier to appreciate by comparison with reference material but the best guide is the form of the tarsi. In B. longitarsus the tarsi are longer with all segments elongate, in the present species the difference is best appreciated by looking at the second segment, especially on the hind tarsi, which is quadrate or slightly transverse.