Curious: spiders "sailing" on the water

High-stretched legs or hind legs as sails help to overcome enormous distances

This spider uses a spider thread as anchor, so as not to be aborted uncontrollably. © Alex Hyde
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Skilled sailors: Spiders are by no means helpless when they fall into the water - quite the contrary. So, some stretch their legs or the back body like sails in the air to be driven by the wind. Others throw spider webs to anchor themselves to the water surface. Others, with the help of their water-repellent legs, are tripping along the surface, as researchers in the journal BMC Evolutionary Biology report.

Spiders have more movement tricks than just crawling: some beat flickflacks, others use filaments and even small nets to get blown away by the wind. "This airborne proliferation is even one of the most influential mechanisms that allow spiders to travel large, even intercontinental distances, " explain Morito Hayashi of the University of Nottingham and his colleagues.

Darwin was astonished

"Even Darwin has already reported flying spiders that fell on the beagle's deck miles from any land, " says Hayashi. But it was precisely this air transport over the lake that provided the guesswork among biologists. Because for the spider, the risk is enormous, crash and then, as it were, shipwrecked stuck on the water or even drown. Actually, this distribution would be much too risky.

Or maybe not? The researchers have put the sample to the test and let 21 species of spiders sail over a water surface in the laboratory. A fan provided wind speeds of just under 0.03 to 0.8 meters per second. They watched the spiders behave when they hit the water.

Legs as sails: This spider can be moved forward by the wind © Alex Hyde

Sailing with legs or handstand

As it turned out, the spiders used six very different strategies to deal with this unfavorable situation. "We've found that the spiders actively take positions that allow them to control their movement on the water with the help of the wind, " says Hayashi. That could explain how the spiders can traverse harmless inlets or even whole oceans. display

Some spiders responded to their involuntary landing by stretching their legs high and sailing over the water, driven by the wind. "The sailing spiders glide gently and steadily over the water, without creating turbulence, " the researchers report. Others chose the head-over method: they raised their hind legs as sails and stood almost in a handstand. Although some spiders remain straight, but began with nimble little steps in front of the wind to trippeln on the surface along.

Head down, Popo in the air: This spider uses her hindquarters as a sail. Alex Hyde

Net as anchor

For other spiders, a secure anchorage was obviously more important than a quick move: they produced spider silk that held them like a net or an anchor on the water's surface. "That's how they slowed down their sailing or stopped altogether, " the researchers say. But there were also spiders that simply killed themselves: they remained motionless on the water surface probably not to attract by Umherzappeln fish and other predators.

Overall, the best air sailors seem to be the most talented sailors on the water, as Hayashi and his colleagues report. Actually, no wonder, because for them the risk of involuntarily landing in the water is greatest. "But if landing on the water is no longer a problem, then you can cover enormous distances in a week or two, " says co-author Sara Goodacre of the University of Nottingham. (BMC Evolutionary Biology, 2015; doi: 10.1186 / s12862-015-0402-5)

(BioMed Central, 03.07.2015 - NPO)