The fan of a Rhagovelia water strider.
Credit: Abderrahman Khila
Some water striders – insects that walk on the surface of water – have an unusual way of getting around.
Bugs of the genus Rhagovelia have evolved fan-like structures on the tips of their legs that they use to move upstream, against the current, in ways that other water striders can’t match.
While a large group of insects, known as Gerromorpha, can walk on the surface of streams and lakes due to water-repellent hairs on their legs, Rhagovelia are specially adapted for fast-flowing water.
The extensions on their second pairs of legs act like flippers that propel them through the water.
Recent research has traced the origin of the swimming fans to mutations in just two genes, which are active only in cells at the tips of the middle legs.