Spiders Can Sail Like Ships Across Water Say Scientists

Posted on July 7, 2015

A water traveling Tetragnathid spider is using silk as anchor

Scientists have discovered how spiders are able to travel across water. Researchers led by Morito Hayashi from the Natural History Museum say spiders can travel over water like ships using their legs as sails and their silk as an anchor. This enables spiders to quickly colonize new areas. A tetragnathid spider is pictured above using its silk as an anchor.

It was already known that some spider species use a technique called ballooning to travel through the air. They use their silk to catch the wind. Spiders can travel as much as 30 kilometers (18.6 miles) when ballooning in the best wind conditions. Now it is known that spiders can also travel over water. The water travel method also helps when ballooning spiders fall from the sky into water.

Hayashi says in a statement, "Even Darwin took note of flying spiders that kept dropping on the Beagle miles away from the sea shore. But given that spiders are terrestrial, and that they do not have control over where they will travel when ballooning, how could evolution allow such risky behavior to be maintained? We've now found that spiders actively adopt postures that allow them to use the wind direction to control their journey on water. They even drop silk and stop on the water surface when they want. This ability compensates for the risks of landing on water after the uncontrolled spider flights."

The researchers studied 325 spiders from 21 different common species found on small islands in Nottinghamshire, UK. They then observed the behavior of the spiders when placed in trays of water in reaction to pump-generated air. They compared this reaction to the spiders on a dry surface. The researchers found many of the spiders adopted elaborate postures to take advantage of the wind current while in the tray of water. They also found that spider species that are known for "ballooning" are also the most able sailors.

Sara Goodacre, a co-author of the study from from the University of Nottingham, says, "Being able to cope with water effectively 'joins the dots' as far as the spider is concerned. It can move from one land mass to another, and potentially across huge spatial scales through the air. If landing on water poses no problem then in a week or two they could be a long way away from where they started."

A research paper on the sailing spider study can be found here in the journal, BMC Evolutionary Biology. The researchers not in the report that "spiders are often able to survive for long periods without food thus water trapped spiders potentially persist for sufficient time to colonize otherwise out-of-reach, distant habitats."

Photo: Alex Hyde