Berosus signaticollis (Charpentier, 1825)

This widespread and locally common species occurs in lowland marginal situations throughout Europe, from North Africa to Southern Scandinavia and from Portugal east through Asia Minor to west and central Siberia; in the UK it is generally common through southern and central England and South Wales, becoming scarce further north to southwest Scotland. The typical habitat is margins of shallow, often temporary pools in a range of situations, including brackish environments, but they are often very abundant around stagnant heath and moorland ponds exposed to the sun. Within the Hydrophilidae they are among the most adapted to an aquatic lifestyle; adults respire from air trapped beneath the elytra and this is oxygenated from a plastron held beneath the body, the beetles surfacing occasionally to replenish this by breaking the water surface with their hydrophobic antennal clubs and connecting the plastron to the atmosphere, larvae respire using long tracheal gills on the abdominal segments, a feature which will distinguish them from most other aquatic hydrophilid larvae which respire by hanging upside down beneath the surface and exposing spiracles at the abdominal apex to the air. Adults occur year-round; they become active in early spring and persist into late autumn with peaks in abundance during early spring and autumn, they fly in the evening and at night, occasionally occurring at light traps, and are very effective colonizers appearing in the most temporary of habitats e.g. woodland and moorland puddles and small pools caused by rain and may appear in stagnant garden ponds etc. New generation adults mate either in the autumn or the spring after overwintering in marginal habitats, eggs are deposited on aquatic vegetation in a silk ‘cocoon’ and larvae emerge after a week or two, they develop rapidly and pass through three instars before leaving the water to pupate in a cell among marginal soil and roots etc. Adults are phytophagous and possibly also detritivores, often occurring in numbers among mats of algae, while the larvae are predatory, feeding upon a wide range of small aquatic animals. They are thought to be univoltine in the UK.