This is the most common corixid in Northants and with a little more recording will be recorded in all 10km squares. It occurs in a wide variety of habitats especially alkaline open clean lakes, open reed beds, canals, ditches, sandy shallow ponds, silt ponds, flowing canals and on clay and rivers. Almost all habitats have flowing water, a low amount of organic matter in solution, little fouling from animal excreta or dead leaves, some shallows and a neutral or alkaline reaction (S&L, 1959).

It flies regularly but is a poor flyer and does not cover great distances. It is readily found in high numbers in light traps. However (J, 1986) explained that the specimens that did not find a siuitable body of water for landing before dusk, are attracted to the lights. The fact that they arrive at lights only during the first few hours of darkness suggests that these do not really fly in the darkness, but if darkness catches them while they are flying, they continue to fly as long as they can.

Bugs over-winter as adults and mate and oviposit during late March and April: there is a second generation, adult from late July onwards, which overwinters.

Distribution:

This is a very common bug across Northants appearing in 75 5km squares and 32 10km squares.

Habitat:

It occurs in a wide variety of habitats especially alkaline open clean lakes, open reed beds, canals, ditches, sandy shallow ponds, silt ponds, flowing canals and on clay and rivers.

Identification:

For the identification of this bug I rely initially on eliminating other species. A blunt ziphus means not a Hesperocorixa sp., no dark patches on palae or tibia and the medium size (c. 7mm) eliminates the larger and smaller corixids.

S.dorsalis rounded ziphus

S.dorsalis rounded pronotum

The pronotum has 6 pale lines and the edges are rounded as above (to differentiate from S.falleni, S.iactans and S.distincta). There is a difficult separation with Sigara striata but this has a restricted distribution and not found in Northants. The male palae have a distinctive set of pegs with S. striata 2nd set are more down curved while S.dorsalis are more evenly curved as below.

Photo: Graham Warnes

Male palae S.dorsalis