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.
Helophorus aequalis 1
Helophorus aequalis 2
Helophorus aequalis 3
Helophorus aequalis 4
4.5-6.5 mm. Distinguished by the large size, smoothly striate elytra which include a scutellary striole, and the denticulate margin of the apical abdominal sternite. In these respects it is similar only to H. grandis Illiger, 1798, which is on average larger (although there is plenty of overlap) and has the forebody more strongly granulate, the apical sternite is more strongly and regularly denticulate, this consisting of deeply incised and squared teeth whereas in the present species they are much smaller and usually irregular. Males may be separated by the size of the aedeagus; in aequalis <1.0 mm, in grandis >1.0mm. Colour varies but in typical specimens the forebody is bright metallic green or bronze, sometimes with the pronotal impressions contrasting, and the elytra are dull brown, sometimes with paler markings and often with a variously-developed darker inverted V- or Y-shaped marking about the middle, appendages pale brown, often with the extremities darker. Head transverse with large asymmetric eyes and a strongly-impressed Y-shaped impression above, surface finely punctured and variably though towards the eyes strongly and often confluently granulate. Pronotum transverse, broadest in front of the middle and sinuate before obtuse posterior angles, apical margin curved between weakly-produced anterior angles, surface densely granulate, these flattened and extensively fused, especially between the sub-median grooves. Elytra smoothly curved from obtuse shoulders to a continuous apical margin, all striae strongly punctured and impressed into the apical third and continuing to the apex, oblique impression below the shoulders usually shallow and only poorly-defined (especially so when compared with H. grandis).