Haliplus fulvus (Fabricius, 1801)
This is a widely distributed western Palaearctic species occurring from North Africa to the far north of Scandinavia, the Faroe Isles and Iceland, and east through the Caucasus, Asia Minor and Kazakhstan to Siberia. It also occurs, though is generally very local and uncommon, across Canada and the northern United States. Across Europe it is locally common though sporadic and in places e.g. Poland generally, rarely encountered, it occurs from lowland to low mountain regions extending above the tree line. In the UK it is locally common throughout, including all the islands north to Shetland, in a range of habitats; typically still water e.g. reservoir margins, drainage ditches and ponds with plenty of vegetation but also slow-moving water, acidic pools on heath and moorland and brackish pools at the coast. Adults occur year-round, peaking in mid-summer but they generally occur in small numbers and often among larger numbers of other common species such as H. ruficollis (DeGeer, 1774) and H. immaculatus Gerhardt, 1877 (etc.), through the warmer months they will occur by general sweeping or by examining floating or marginal debris and through the winter beneath partly submerged timber or among marginal litter. Mating occurs in the spring and eggs are laid in the stems of aquatic plants, larvae develop through the spring and summer and overwinter either in the water or, if fully grown, among marginal litter like the adults, and pupate among the substrate in the spring; in northern latitudes the new-generation adults appear very early in the spring but will not reproduce until the following year whereas in more southern European latitudes they will reproduce in their first spring. Larvae feed entirely upon algae while adults are omnivores, feeding upon algae as well as early stages of other insects e.g. eggs of midges etc. that are laid in the water. Adults fly well and may quickly colonize new habitats.
The relatively large size and mottled appearance soon become distinctive in the field. 3.5-4.5mm. Elongate and broadly oval, widest about the middle evenly rounded to an acuminate apex. Pale yellow to dusky yellow or light brown with various distinct darker markings to the elytra, and sometimes the base of the head is darkened. Dorsal surface with (usually sparse) very fine punctures which become obvious at X40 as well as scattered larger punctures on the head, pronotum and elytral interstices. Pronotum with a series of large punctures before the basal margin but without an impressed line either side of the middle, laterally meeting the elytra at a wide obtuse angle. Prosternal process flat, without grooves or fovea, and with lateral margins distinct to the anterior edge of the pronotum, metasternal process with a small impression which is obviously much larger than the surrounding punctures. Elytra with sloping shoulders and broadest about the middle, striae consisting of rows punctures which are larger towards the base but without any much larger punctures along the basal margin, dark markings mostly discrete and extending over one or two striae although those on the disc may be partly confluent. On the continent this is a very variable species with entirely dark or pale specimens occurring, in the UK it is less so although some specimens from the north of Scotland have reduced elytral markings. Among our UK species which lack basal pronotal striae and strongly punctured dorsal surface the present species may be known by its large size; H. variegatus Sturm, 1834 and H. laminatus (Schaller, 1783) are always less than 3.5mm., the discretely marked elytra; H. mucronatus Stephens, 1828 lacks these dark markings and in H. variegatus they are much more extensive and confluent, and the form of the prosternal process; in H. flavicollis Sturm, 1834 the sharply-defined lateral borders do not extend to the anterior margin of the prosternum. Our other species either have the basal pronotal striae or have the dorsal surface extensively and strongly punctured, this being obvious at X20.