Flying spiders able sailors

Using their legs as sails and their silk as an anchor, some spiders can travel across water like ships, new research says.

The study helps explain how spiders are able to migrate across vast distances and why they are quick to colonise new areas.

"Being able to cope with water effectively 'joins the dots' as far as the spider is concerned," said study co-author Sara Goodacre from the University of Nottingham in Britain.

The study said the ability to float on water keeps spiders safe if they land on water after an uncontrolled flight.

Common spiders are frequently observed to fly using a technique called 'ballooning'. This involves using their silk to catch the wind which then lifts them up into the air.

Ballooning spiders are estimated to move up to 30 km per day when wind conditions are suitable, helping in their quest for new habitats and resources.

This dispersal strategy, however, involves a significant risk. The airborne spider has little control over where it travels and could end up landing on water, which has been thought to be unsuitable for its survival.

"We have now found that spiders actively adopt postures that allow them to use the wind direction to control their journey on water," lead author Morito Hayashi from the Natural History Museum, London, said.

"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," Hayashi said.

For the study, the researchers collected 325 adult spiders belonging to 21 common species from small islands in nature reserves in Nottinghamshire in Britain.

The spiders' behaviour was observed on trays of water in reaction to pump-generated air, and this was compared to their reactions on dry surfaces.

The research team also found that the spiders that adopted 'ballooning' behaviour for airborne dispersal were also the most eager and able 'sailors'.

The study was published in the open access journal BMC Evolutionary Biology.