Hesperocorixa sahlbergi

Hesperocorixa sahlbergi is a widespread species that occurs in ponds, lakes and ditches rich in organic matter (i.e. dead leaves and muddy sediment), usually alkaline and with a high level of organic matter in solution. It is often found in woodland ponds with a covering of duckweed. The overwinters adults mate in early spring when the water is still quite cold and the resulting nymphs take at least two months to develop into adults. The bugs are detritus feeders and breathe dissolved oxygen as early nymphs but by means of a bubble gill, which requires renewal at the surface from time to time, in later nymphs and adults. H. sahlbergi readily migrates and may be taken in light traps.

The map is based on records from NBN Gateway, with yellow dots showing pre 1990 records, reds dots 1990 – 2017 records and red on yellow dots overlapping records. Hesperocorixa sahlbergi is widespread in Ireland

Hesperocorixa spp are distinguished from other groups of lesser water boatmen (Corixidae) by the pale lines on the wingcase which are narrow and extend more or less unbroken across the dark background. In the case of the two larger species, H. sahlbergi (7.0 – 9.0 mm) and H. linnaei (7.0 – 8.0 mm) , there is a distinct contrast between the pale lines and the dark background. In the two smaller species, H. moesta (5.5 – 6.0 mm) and H. castanea, there is little contrast. In all species the metersternal xiphus is much longer than its breadth at the base. H. sahlbergi can be distinguished from H. linnaei by the 7-9 pale lines on the pronotum (H. linnaei has 6) and the pattern of light lines on a dark background fading towards the apex of the corium (in H. linnaei the pattern continues to the apex).