The water strider (family Gerridae ) ‘walks’ on the water surface producing chromatic edged dark patches – not shadows – on the pond bed beneath. Photographer Andrew Kirk.
A water surface acts as though it has a tightly stretched elastic skin. This results from the slight but cumulative attractive forces between water molecules .
Without the ‘skin’ small creatures would no doubt have evolved in a way that did not involve them walking on water surfaces.
Small creatures are supported because their legs are not wetted. They do not penetrate the water surface. Instead they depress it into a curved meniscus.
The surface tension forces combine to produce a net upthrust that counters the insect’s weight. With care and guile we can similarly support small metal objects on water. Imagine also walking across a trampoline.
Gerridae is a family of true bugs in the order Hemiptera, commonly known as water striders, water bugs, magic bugs, pond skaters, skaters, skimmers, water scooters, water skaters, water skeeters, water skimmers, water skippers, water spiders, or Jesus bugs. One main characteristic that sets gerrids and other true bugs apart from other insects is that the front wing is only half functional.
Rather than using it for flight, it acts as a membranous covering and the thickened part is by where claws develop. Consistent with the classification of Gerridae as true bugs, gerrids have a mouthpart evolved for piercing and sucking, Gerrids distinguish themselves by having the unique ability to walk on water.
Gerridae, or water striders, are anatomically built to transfer their weight to be able to run on top of the water’s surface. As a result, one could likely find water striders present in any pond, river, or lake. Scientists have identified over 1,700 species of Gerrids, 10% of them being marine.