Helophorus aequalis Thomson, C.G., 1868

This generally common western Palaearctic species occurs throughout most of Europe north to the UK and into central provinces of Fennoscandia and east into Asia Minor to the south and parts of western Russia further north. It is very common and often abundant across England, Wales and southern Scotland, including all the islands, and more local though no less common further north to Shetland and across Ireland. Adults occur year-round although they are rarely found during the winter, they become active from early in the spring and remain so into October or November, peaking in abundance during June and July. Typical habitats are stagnant freshwater pools and slow-moving stretches of rivers with plenty of algae and patchy marginal vegetation but adults fly well, especially in the spring and early summer, and may occur in at any source of water such as peat bogs, garden ponds, cattle troughs, flooded tyre ruts and puddles in almost any situation, they have also been recorded in brackish coastal pools and on sandy beaches. Mating occurs through the warmer months and egg-laying begins in the autumn although these will not hatch until the following spring when the majority of oviposition occurs, and in colder years and at higher latitudes oviposition occurs exclusively in the spring. Females deposit cocoons containing up to twenty eggs among damp marginal substrate and larvae emerge soon afterwards, larvae roam among marginal substrate predating small insects etc. and are fully-grown in about two weeks when they pupate among moss etc. near the water edge. Adults are vegetarian, feeding mostly on algae in damp marginal situations, they often appear among samples of aquatic vegetation and may be present in large numbers on damp substrate among marginal plants, mating pairs may be found commonly through the spring and early summer but rarely so when the hot weather begins and many temporary water bodies vanish.