Even though there was a frost last night and the pond surface briefly froze, there were two pond skaters Gerris lacustris out hunting by mid-morning, on the lookout for any small insects that had become trapped in the surface film .....
..... like this one. At this time of year most of the prey items are small but in summer I've sometimes seen pond skaters descending like a pack of wolves on drowning wasps.
This one, with a nightmarish countenance, has caught a small fly whose wing you can see held between the short front legs of the predator.
The pond is currently suffering from an algal bloom which slows down the skaters' progress across the surface and sometimes clogs the microscopic hairs that makes these hunters water-repellent. They are spending a lot of time grooming the algae off their body surface and when they do this, grooming the second leg against the third leg on each side in turn, they use one of those short prey-capture legs at the front as the third leg of a tripod to support themselves - normally, when the animal is on the move, the front legs are held just above the water surface. The greenish-yellow deposit on that middle leg on the left-hand side in the picture is a patch of algal cells that the insect hasn't managed to remove yet.
At the moment there are only two pond skaters present and the larger one, top left, is the female. They seem to be courting, by slowly approaching and extending a middle leg towards each other. They breed in May so she'll be laying eggs now and by the end of the month I'm expecting to see nymphs scooting across the surface.