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Saturday, 4 July 2015

Some spiders are great sailors that can traverse oceans, scientists say


(CNN)Spiders are invading from the sea. Scientists say so.

But that's no reason for arachnophobes suddenly to start climbing flag poles. A select number of creepy-crawlies have been doing this for eons, researchers now say, because a good many of them can sail quite adeptly.

They can harness wind, weigh anchor and toss a line to a raft.

Also, poles wouldn't offer arachnophobes a complete escape, because many spiders can fly, too, by catching a breeze in lines of web they spew from their abdomens, a feat called ballooning. It can take them to the neighbor's yard or to a neighboring continent.

Ballooning is not news to scientists. It has led to some species spreading to new habitats like wildfire, making them part of most every ecosystem on land.

But previously, arachnologists thought the ballooning spiders' flying range abruptly ended at the water's edge, because after landing in a pond, a creek or the ocean, they'd be helpless.

If that were the case, then why are a large number of spider species found on most continents, the scientists asked? And why have spiders been seen floating alive in the middle of oceans?

Sure, there are aquatic spiders that have evolved to revel in the wet, but they're in the minority, and they aren't the spiders that piqued the researchers' curiosity.

Instead, they wondered how the teeming masses of crawly land lovers, the purely terrestrial spiders, overcome oceans so well. On top of that, spiders are great pest controllers, so knowing how they move can be beneficial to agriculture.

"We really want to know more about where they go, what they eat, how they move, how they get to a farmer's field -- for our own benefit," said Sara Goodacre, head of Spider Lab at the University of Nottingham in Britain.

325 spiders dumped in water
So, the researchers collected 325 wild spiders and dropped them onto water to see how they dealt with it.

A note for arachnophobes: The spiders they chose, linyphiids, are not the scary, horror movie variety -- they're more like the itsy bitsy spider of nursery rhyme fame that crawled up the water spout. They are about half the size of a dime, legs included, often go unnoticed, and aren't harmful to humans.

They helped the scientists break the mold of previous thinking on spiders and sea travel. The researchers published the results this week in the journal BMC Evolutionary Biology.

All 325 spiders floated on their feet, which turned out to be water resistant.


And many of them pulled off wind-surfing ballets, catching the breeze by stretching legs upward or doing a "hand stand" on all eight legs and protruding their abdomens into the air.

The wind flicked the spiders over the water surface like air-hockey pucks.

And the spiders did all this specifically when on water. When confronted with wind on a dry surface, almost all of the spiders hunkered down to duck out of the gust.

Fliers are also good sailors
About a third of the spiders that were tested showed ballooning behavior -- and turned out to be good sailors at the same time. "The propensity for sailing appears to be tightly linked to the tendency for aerial dispersal," the arachnologists wrote.

These spiders were true Marines -- going most anywhere by land, sea or air.

Some spiders showed off handy seafaring skills to boot. If the wind was too much for them, many shot a line of silk onto the water as an anchor to slow themselves down.

"Our observations suggest that a possibility could be that the silk may sometimes work as a dragline for the water-trapped spider to attach to floating objects or to the shore," the scientists wrote.

If a stick floated by, they zapped it with string, connected the other end to the water's surface and roped over to the object to use it as a raft -- or potentially more.

"A spider that reaches a floating tree, for example, might be able to become airborne by ballooning from its surface, or from one of its non-submerged branches," the researchers wrote.

Some spiders go anywhere
The big takeaway for the arachnologists? The spiders' quest for new land does not end at the water's edge. And since they can go for long periods without food, they can travel very far by water.

That raises the possibility that populations of spiders around the world are genetically more closely connected than previously thought.

The big takeaway for arachnophobes? Climbing poles is futile.

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