Cymatia bonsdorffii is a widespread species, occurring in a range of habitats but with a preference for well vegetated ponds and lake margins. It has a wide tolerance of pH, although has been reported to favour acidic conditions. Unlike most corixids, C. bonsdorffii is a predator and feeds on a variety of small aquatic invertebrates including mayfly nymphs, water fleas and chironomid larvae. It rests on vegetation facing into open water and is able to dart out at great speed to capture prey with its cylindrical fore-tarsi and middle legs. C. bonsdorffii exhibits alary (wing) polymorphism – although the forewings are fully developed, the hind wings may either be fully formed (macropterous), allowing the bug to migrate, or reduced (brachypterous). The latter is the common condition and fully winged forms are rare. This species overwinters as an adult and mating occurs in May – June to produce a summer generation in July / August. Whether or not these adults give rise to a second generation, or overwinter themselves, is uncertain.
The map is based on records from NBN Gateway, with yellow dots showing pre 1990 records, reds dots 1990 – 2015 records and red on yellow dots overlapping records. Cymatia bonsdorffii is fairly widespread in Ireland.
Cymatia bonsdorfii is 6 – 6.5 mm in length. Identification is fairly straightforward, based on distinctively patterned forewings and a plain brown pronotum.