Seafaring spiders use legs as sails, silk as anchor

Scientists had previously learnt that spiders could take to the air on “ballooning” flights, using their silk to catch the wind. A spider launches its silk upwards where it forms a triangular parachute which catches the wind and propels the spider through the air.

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The team found that spiders adopting the “ballooning” flights were also the most eager and able sailors.

Ballooning spiders are estimated to move up to 30 km per day when wind conditions are suitable. “Spiders were thought to colonise exclusively by air; maybe they are good sailors too”. “We have to change our idea of risk concerning ballooning”, he says. Essentially, the spider touches the water and freezes.

Aerial dispersal has thus been seen as something of a roulette wheel for spiders; the possible benefits of moving to better habitat is counteracted by the risk of a watery grave.

The study published in the journal Evolutionary Biology claims that spiders can sail like ships using their acrobatic bodies.

The research was led by Morito Hayashi and Sara Goodacre of the University of Nottingham.

The researchers collected 325 adult spiders from 21 common species from small islands on nature reserves in Nottinghamshire. These spiders were then taken back to the universities “Spider Lab” for testing.

The researchers observed the arachnids sail across the water in turbulent, still, fresh and salt water conditions. Most notably, numerous spiders demonstrated what the researchers term “sailing” behavior. He added that whenever spiders feel the need to drop silk, they do so and stop on the water surface.

When exposed to a breeze on solid ground, they showed none of the behaviours, which suggests these are used specifically for sailing.

Floating spiders may use silk to slow down their passage or latch onto floating objects.

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

Silk is released onto the surface of the water. “Because 70% of our planet is covered by water, if they’re ballooning, they have to face landing on water”, says Hayashi.

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“Upsidedown sailing: when on water, the spider reacts to the wind and raises its abdomen as a sail, in a handstand-like posture, and slides on water”. “Death mimicry behavior is likely to be a predator avoidance strategy, as is common to many animals”. The association between the two behaviors may indicate the importance of ballooners also being able to sail, which could be invaluable when landing on water.

Airborne spiders can sail on seas : Nature News & Comment