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There are 69 species of Water Bug in Great Britain making them a easier but fascinating group to start identifying. On first glance, they can be similar to beetles, but all bugs have a pointed mouthpart (Rostrum) and their wing cases are more lethery than shiny and have a flap or membrane at the end that overlaps rather than a line down the centre.
There are two main groups of Water Bugs. One are skaters or surface bugs like Water Crickets or Pond Skaters and secondly there are Boatmen or swimming bugs like Water Boatmen, Backswimmers or Saucer Bugs.
As with most groups there are varying difficulties to identification and unfortunately the Pond skaters (Gerridae), the Lesser water boatmen (Corixidae) or Backswimmers (Notonectidae) do have similar species so it is not always easy to tell the common species without close inspection sometimes under a microscope. However to help with this I have created a simple key to the Water Bug Families and also a Photograph identification guide.
To get started though there are six very distinct and easy to identify Water Bugs that are really fascinating and you should be able to find Five in most water bodies and one that is a specialist of fast flowing water. They are:
Water Scorpion (Nepa cinerea)
This is large at c20mm although juveniles look very much the same as well but smaller versions. It is extremely distinctive with it's modified front legs to grab and hold it's food, flat body shape as well as the long tail that it actually uses as a breathing tube. It is common in ponds, lakes, canals and at stream edges... More info
Water Stick Insect (Ranatra linearis)
This is not a difficult species to identify as there is nothing else in the water with a long rounded body, 30-35mm long with the long breathing tube looking like a tail. The juvenilles look very similar but smaller. It is very difficult to see in the tray as it does look like a number of sticks together. It is widely scattered and prefers deeper ponds and lakes... More info
Saucer Bug (Ilyocoris cimicoides)
This is very distinctive because it is large (13.5mm), flat and also has a jagged edge to it's body. There is a smaller relation but this is only found in a very small number of locations in the south east. This bug is found at the bottom of muddy and stagnant ponds amongst vegetation where it hunts other invertebrates... More info
River saucer bug (Aphelocheirus aestivalis)
This is also disctincive being 8-10mm, round, flat and matt brown with a jagged edge to its body. Quite often it's large pointed mouthpart from the front of its face is visible or it is tucked under it's body. This is a fast water specialist and prefers riffles and fast water over rocks and gravel... More info
Water Measurer (Hydrometra stagnorum)
This is a real dainty bug walking on the waters surface around the margins of ponds and streams in the slack water. It is long (9-11.5mm) and thin with dainty legs and a distinctive long head with the eyes a third of the way along. There is a smaller relative but this is currently confined to just a few sites on the east coast... More info
Least Backswimmer (Plea minutissima)
This is a tiny, 2-3mm, sandy coloured bug and can be seen swimming upside down quite fast. At a quick glance, it can be mistaken for a beetle but nothing else has the boat shaped body. It lives in dense weedy areas of ponds, pools, slow rivers and dykes... More info
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