This is a backswimmer or greater water boatman swimming mainly upside down and have two large hind legs with swimming hairs that look like paddles. It is quite distinctive in the field by the dark X mark on paler powdery forewings.

It is a more southern species that is tolerant of salinity and found in coastal areas however it is also found in non-saline pools in the midlands.

The life-cycle is similar to that of N.glauca but oviposition is usually completed in 2 weeks (SWL, 1959)

Distribution:

This is a lowland Southern species that is extending it's range into Wales in lowland areas (absent from uplands) but also Northwards but not Scotland yet. It is fairly common in Northants and widespread around the county seeming to abundant in the Nene Valley pits.

Habitat:

It can tolerate salinity and therefore mainly associated to casual areas. However it is also now associated with non-brackish midlands pools and lakes. It can be abundant in the Nene Valley Gravel and Clay Pits

Identification:

This can be differentiated from the other 3 Notonectidae by appearance. The ground colour of the forewing is light and can be more powdery with the dark mark at the intersection of the hemelytra more an X shape. It also is a little smaller than the others but this is difficult to tell without them being side by side. Also a defining feature is that the pronotum extends to a point partly round the eye, although this is difficult to see in the field without close inspection.