Spiders Sail Across Water Using Their Silk as an Anchor

Common spiders can frequently be seen flying due to a technique called "ballooning." This is when a spider uses its silk to catch the wind to journey through the air. It's estimated that these spiders can move up to 30 km per day when wind conditions are suitable.

Yet this mode of transportation involves a significant risk. The spiders have little control over where they travel.

In order to better understand spider dispersal, the researchers collected 325 adult spiders belonging to 21 common species from small islands in nature reserves. The scientists watched the spiders' behavior on trays of water in reaction to pump-generated air. This was then compared to their reactions on dry surfaces.

Many of the spiders adopted elaborate postures, such as lifting up a pair of legs, to seemingly take advantage of the wind current while on the water surface. This, in particular, allowed them to "sail" in turbulent, still, fresh, and saltwater conditions. By releasing silk on water, the spiders were also about to "sail" by dropping "anchors" of silk to slow down or stop their movement. This suggests that the silk may sometimes work as a dragline for a water-trapped spider to attach to floating objects or the shore.

"Being able to cope with water effectively 'joins the dots' as far as the spider is concerned," said Sara Goodacre, co-author of the new study, in a news release. "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."

The findings reveal a bit more about these spiders and show how they can manage to disperse in such an effective way.

The findings are published in the journal BMC Evolutionary Biology.

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