Anthocomus rufus (Herbst, 1784)
This species has a limited and patchy European distribution; it is locally common in the west, from Portugal, Spain and France, extending east to Italy, Poland and Austria and north to Sweden and the UK although absent from the Benelux countries and Finland, here it is locally common and often abundant across south and central England north to the Humber, it is generally absent from the west Country and in Wales it is mostly south-coastal. Adults occur from June until October in wetland habitats, especially around reedbeds and still-water margins, where they are active during sunny spells and may be observed mating throughout the season. They mate on foliage or stems and this may occur quite quickly and spontaneously or they may perform a courtship ritual where they approach and walk around each other; the male may stimulate the female with his antennae and the pair will rotate so that the male is facing away from the female while she nibbles at tufts of setae on his elytral apex and this may go on for ten minutes before they mate. They are predatory and hunt small insects etc. among the foliage but also spend much time consuming pollen, typically on reed flowers (Phragmites communis) but also on rushes (Juncus) and various sedges. Soon after mating females lay eggs in empty seed cases or among reed flowers where the larvae will develop feeding on dead insects etc. Larvae overwinter in reed stems and pupate within the stems from late spring. Adults rarely occur far from marginal foliage, they often aggregate on plants or swarm in flight and will frequently be observed with the bright-red thoracic and abdominal vesicles extended as they sit on leaves and stems, they may be easily swept or tubed directly and later in the season, when the water level has fallen, they may be seen in numbers among stems and litter on damp soil.
This small but very distinctive beetle should not be confused with any other in the UK; the colouration alone is sufficient to identify the species. Head shiny black and rather flattened, with sparse and fine punctures and pubescence and relatively large and convex eyes. Mandibles bidentate, maxillary palps 3-segmented with the terminal segment fusiform. Antennae inserted anteriorly on the outer margins of the clypeus, long and robust with the second segment small, 3-7 weakly serrate and 8-11 elongate. Pronotum transverse and flat or depressed inside the posterior angles, surface finely punctured and pubescent, red but for a wide longitudinal median dark area. Prosternum red but for a dark area anterior to the coxae. Scutellum and surrounding area of the elytra dark. Elytra elongate and gradually broadened from the basal third, more strongly so in the female, with well-developed shoulders and continuously rounded apical margins. Surface finely rugose and punctured and with fine recumbent red pubescence. The male elytral apices have a specialized structure called an excitator, this consists of a curved and raised black tubercle set among the pubescence, at the base is a gland which produces secretions consumed by the female before copulation. Legs long and slender, with notably long trocanters, long unarmed femora and long slender tibiae. Tarsi 5-segmented.