Some Spiders Can “Sail” Across Water

Whether it’s one creeping around some dark corner of your house or crawling over its web in a field or forest, most spiders we encounter are found on solid ground. Some spiders aren’t entirely earth-bound, though. They’re also masters of air travel and, it turns out, sailing.

Many kinds of spiders are able to take to the sky by using strands of silk like a parachute to catch a breeze and ride it, a behavior known as “ballooning.” It’s a great way to get around, and helps explain why some spiders are so widely distributed and are often early colonizers of new habitats. There seems to be a major flaw in these spiders’ travel plans, though.

The problem, says a team of scientists led by biologist Morito Hayashi and Sara L. Goodacre, is that while they’re “able to control the decision to become airborne or not, ballooning individuals cannot predict where and how far they will travel.” Sometimes these flights can carry spiders far away from where they started and even out to sea, where they’ve been found in the sails and on the decks of ships on the open ocean, hundreds of miles from land. While some spiders are adept on the water, scurrying across the surface or making diving bells for swimming, scientists have usually considered water landings—whether in the ocean or in a puddle—a death sentence for ballooning spiders.

That’s not always the case, according to Hayashi and Goodacre, who have found that many common spiders get around at sea as easily as they do on land and in the air, and can use their legs and silk as sails and anchors to travel across the water.

Hayashi first noticed the behavior while studying the spiders’ take-off techniques in Goodacre’s “Spider Lab” at the University of Nottingham. To learn more, the researchers collected more than 300 spiders belonging to 21 different species in the wild and brought them back to the lab. There, they used an air pump to see how the spiders reacted to breezes while on dry land or in trays of water. 

On the water, most of the spiders reacted to the wind by raising their front legs or lifting their abdomen up in a handstand posture, allowing them, as the scientists write, to “smoothly and stealthily slide on the water surface without leaving any turbulence.” Some of these little sailors also tossed out lines of silk into the water “like ships dropping their anchors to slow down or stop their movement.” A few even attached their silk to the edge of the tray as they passed so they could haul themselves out of the water.

When the spiders were hit with the air pump while standing on a dry lab table, only a single spider briefly raised its front legs. The rest either kept walking around normally or hunkered down and tried to resist the wind, leading the researchers to think that the sailing behaviors are exclusively tied to being on the water.

Hayashi and Goodacre want to do more experiments with the eight-legged mariners to see how well they sail in more natural conditions, and how much turbulence they can handle in the water.