Small World Discoveries

HEMIPTERA > HETEROPTERA > GERROMORPHA ('skaters')

The GERROMORPHA infraorder separates the freshwater semi-aquatic surface bugs, collectively known as 'skaters', from the true aquatic bugs that live in the water. They are a varied group of small predatory species that typically live amongst the marginal vegetation of still or slow-flowing waters, but spend much of their time actually on the water surface where they hunt for prey. Their light weight, coupled with a body and legs that are covered with fine water-repellent hairs, allows them to both walk on, and rapidly move across, the surface film.  

In Britain there are five families; Mesovelidae (the pondweed bug), Hebridae (two species of Sphagnum bug), Hydrometridae (two species of water measurer), Veliidae (five species of water cricket) and Gerridae (nine species of pond skaters).

Although some of these bugs are quite interesting, I don't think I'll spend much time with them when out and about unless I come across any that can be photographed at close quarters from the pond side or river bank so, at the moment, I'm only able to represent the group with a couple of species that inhabit our small garden pond.

Hydrometridae (Water Measurers)

Elongate, slow-moving, predatory bugs that patrol water margins in search of fleas, mosquito larvae are similar prey that live just below the film of the water surface. Their heads are particularly slim and long with eyes that are located a good way from the base. There are only two species; the common Water Measurer [Hydrometra stagnorum] which is dark brown to black with five pairs of pale spots on the abdomen, typically short-winged, and with a body length of 9-12mm; and the smaller, red-listed, Lesser Water Measurer [Hydrometra gracilenta], which is only found at few sites in the Norfolk Broads and the Pevensey Levels in East Sussex.

Gerridae (Pondskaters)

Long legged, slim bodied, agile and quick-moving, surface predators that can be found on almost any still or slow-moving stretch of freshwater from rivers and streams, to lakes and even small garden ponds. They use their long middle legs to 'row' themselves across the surface in pursuit of prey that they grasp with their shorter raptorial fore legs. Much of this prey is tiny dead or dying invertebrate species that have had the misfortune to be trapped in the water. They have sensitive hairs on their body and legs that detect even small movements across the water, which in many cases allows them to pounce on prey before it has a chance of escaping or being taken by another waterbug. The family consists of nine species, two of which, the River Pondskater [Aquarius najas] and the Lake Pondskater [Aquaris paludum] are classified as nationally scarce. The remaining seven species are all in the Gerris genus. The most frequently observed species by far is the Common Pondskater [Gerris lacustris]. It has a body length of 8-10mm, which is 6mm or so shorter than the significantly larger River and Lake Pondskaters. They are all very similar and, as yet, I've not found a good key or identification guide to distinguish the species. Gerris lacustris has very variable wings from virtually wingless to fully macropterous with these fully-winged forms being strong fliers, which explains how they can so rapidly colonise ponds.