One of my earliest bug memories is watching pond skaters moving effortlessly and magically over the water. Pond Skaters, Gerris sp., also known as Water Striders, are true bugs: they piercing mouthparts are used to suck the juices of the insects they predate. Their legs are clothed with water-repellent hairs and they propel themselves with their middle legs in a flicking glide. Their front legs are small and kept tucked ahead of them, sensing the vibrations in the water from other ponds skaters or potential prey that have fallen in the water, and also grasping and holding their prey. They are seven similar species of Pond Skaters in the U.K., and they are sometimes found in the same pond. Pond skaters are active in these mild days of autumn and will overwinter as adults, moving away from the water with the first frosts. Many pond skaters species are polymorphic and have long-winged and short-winged morphs. In species with two generations per year, the long-winged form tends to be the overwintering generation - which is also the dispersive one - while the summer generation tends to be short winged. When the winter comes, short-winged individuals, unable to fly, will crawl out of the water and hide in the bank, while long-winged ones can fly away from water, to sites that are free from risks of flooding or freezing. In the spring, emerging pond skaters will fly back to ponds and lakes, using the reflections of the water - or other shiny surfaces - as guide.
Pond skaters, as other true bugs, go through five instars before becoming adults. The individual of the top photo is a nymph (24 Jun 2011), the one at the bottom, an adult (2 Jul 2011). Although the photos are from earlier in the year, smaller nymphs were still in a local pond last monday.