Spiders can sail the oceans like ships

Spider are impressively quick to colonize new territory, perhaps second only to winged species among arachnids and insects in their exploratory prowess.

New research suggests one key to their mobility is the ability to travel across water -- like a sailboat.

Researchers already knew spiders often employ a travel technique called ballooning, whereby the crawlers make their way to high ground and hurl out a mass of silk to catch the breeze. In doing so, the spiders quite literally relinquish their fate to the whims of the winds.

But what happens when the whims of the winds deposit the arachnids in the middle of the pond, lake, stream, river or ocean.

"Even Darwin took note of flying spiders that kept dropping on the Beagle miles away from the sea shore," Morito Hayashi, a researcher at the Natural History Museum, in London, noted in a recent press release. "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?"

It turns out, spiders know how to sail.

In a new study, published this week in the journal Evolutionary Biology, researchers demonstrate how spiders use their legs to catch and manipulate the power of the wind, while employing their silk as an anchor.

"We've now found that spiders actively adopt postures that allow them to use the wind direction to control their journey on water," explained Hayashi, lead author of the new study. "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."

Researchers in England collected 325 adult spiders from small coastal islands. The haul consisted of specimens from 21 common species. Researchers observed the spiders sail across pools of water, using fans to replicate different wind conditions.

The scientists found the spiders to take on sometimes elaborate and acrobatic postures, raising and contorting their legs in different directions and angles to take advantage of the breeze. The releasing of silk allows the spider to slow their momentum, or potentially to latch on to larger floating objects.

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