Land ho! Spiders aren't typically stereotyped as animals who are savvy on the sea, but it turns out that some spiders do have sea legs. These spindly skippers use their silk as an anchor and their legs as sails to navigate the seas, a bit like a ship. Avast!
The findings, published in the open access journal BMC Evolutionary Biology, showcase some of the adaptive capabilities of our eight-legged friends.
It has been noted in the past that some spiders use a technique called 'ballooning' to cross bodies of water: This is where spiders take advantage of air currents to 'fly' over the sea. A ballooning spider is estimated to travel up to 30 kilometers (around 19 miles) a day when floating in optimum wind conditions.
Morito Hayashi from the Natural History Museum in London noted: "Even Darwin took note of flying spiders that kept dropping on the Beagle miles away from the sea shore. But given that spiders are terrestrial, and that they do not have control over where they will travel when ballooning, how could evolution allow such risky behavior to be maintained?"
"We've now found that spiders actively adopt postures that allow them to use the wind direction to control their journey on water. They even drop silk and stop on the water surface when they want. This ability compensates for the risks of landing on water after the uncontrolled spider flights."
These findings are based on 325 spiders belonging to 21 common species found in Nottinghamshire, U.K. The spiders were placed in trays of water and on dry surfaces to see how they would react to a pump-generated airflow.
When the spiders placed on water experienced the flow of air, their postures became fancy: They elaborately raised their legs, as though embracing the air current. Some spiders were seen using their silk as an anchor of sorts.
The spiders left on 'dry land', however, did not exhibit this behavior. (Arrgh, them landlubbers!) This suggests that spiders will adapt their behavior when they encounter bodies of water, but don't need to adopt 'sailing' behavior when on dry land. This has implications for how spiders may have been able to disperse to find new habitats and resources.
Central Image: Tetragnathid spider sailing using legs is shown. Alex Hyde.