This is a large surface bug which occurs in colonies on the surface of large open water bodies such as lakes and reservoirs and on flowing water in rivers and canals (PK, 1992). It is similar to Aquarius rajas which it appears to replace in slow flowing or still waters (TH, 2003). 

Eggs are laid beneath the water, the female carrying the male beneath the surface with her. Oviposition extends over a considerable period, and nymphs continue to occur until late in the year. There may be at least a partial second generation. All stages are carnivorous, feeding largely or entirely on arthropods which have fallen or been blown into the water, and are trapped in the surface film (PK, 1992). 

Distribution:

This is at it's northerly range and a species of the South East. Recorded for the first time in Northamptonshire in 2010 by Peter Kirkby the next record i have is from 2017 but it has been found at quite a few locations in Bedfordshire so assume this is under recording in our area. From Tony Cook's review of scarce and threatened bugs he concludes that there has been a large increase in records since 1989 and this is now more widespread in the South East of England. Last year i added another 3 sites of Cambridgeshire records too and this year a further 3 sites for Northamptonshire.

Habitat:

Found in large lakes but sometimes small ponds. It appears to frequent the open water on the edge of the overhanging willows. Also appears to be in the stream as well as the lake. They can be fast and elusive but the best time to see them is in sheltered areas on a windy day when they come in closer to the bank. 

Identification:

These are a large bug when you see them skating on the water of 15mm. They have an all black pronotum with yellow line on both sides. The abdominal spines are longer and quite distinctively angle upwards at the end by 20 degrees.