Spiders can travel across water using their legs like sails and their silk like an anchor.

Tetragnathid spider using silk as anchor. Photo courtesy: Alex Hyde | BMC Evolutionary Biology Journal.

Spiders are able to use their legs like sails and their silk like anchors in order to control their movement across bodies of water. For year, scientists have been aware of a phenomenon called “ballooning” where spiders use a bit of their silk like a balloon to travel through the air.

Doing so can allow spiders to travel up to 30 miles a day, under the right wind conditions. Unfortunately for the spiders, they have little control over where the wind takes them, and they could end up just about anywhere.

Until now, scientists had assumed that spiders that landed on water were in trouble. Darwin even noted this while he was sailing on the Beagle, and wondered how such an uncontrollable and potentially dangerous form of travel could have evolved.

An international team of researchers has an answer now, based on a study of 325 spiders form 21 species native to the United Kingdom.

What they found was that these spiders, after landing on a body of water, could use their legs kind of like sails, allowing them to navigate across great distances if needed. They also used their silk to create draglines and anchors, allowing them greater control over where they’re going.

The researchers figured this out by catching the spiders and then releasing them onto trays of water, where they used pumps to generate breezes that the spiders could react too.

The discovery that some spiders act like tiny sailors goes a long way to understanding how spiders are able to spread to new areas and colonize so quickly. Until now, those were some important and unanswered questions.

Although most of the spiders that could sail were members of species known for ballooning, some were not. Researchers hypothesize that these species may have developed sailing skills to cope with sudden changes in their environment, such as floods.