They can be seen skitting over the surface of still water in ponds and pools. In fact, there are two different species. The Lesser water boatman (second picture) is indeed, as its name implies, smaller. It also looks like it is walking on the water standing upright, whereas the water boatman lies on its back an appears to use its forelegs like oars.
The lesser boatman is vegetarian, the boatman predates just about anything in the pond which it is big enough to catch.