Silky Story: Spiders Sail The Seas, Say Scientists

New research helps solve the secret of how spiders can migrate across great distances, and how they are so fast to colonise new areas. Spiders journey across bodies of water like ships. They use their legs as sails and their silk as an anchor, according to research published in BMC Evolutionary Biology.

Spiders are often observed using a technique called ‘ballooning’ to fly. Ballooning consists of a spider using their silk to catch the wind, lifting them up into the air.

When wind conditions are right, it is estimated, ballooning spiders can moce move up to 30 km per day, aiding in their search for new habitats and resources.

Tetragnathid spider

Tetragnathid spider is using silk as anchor.
Credit: Alex Hyde

But the technique is not without risk, as an airborne spider has scant control over where it goes, possibly even landing on water, which has been believed to be poor for its survival chances.

According to lead author Morito Hayashi of the Natural History Museum, London:

“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.”

The researchers also observed that the species of spiders that adopted ‘ballooning’ behavior for air travel were also the most enthusiastic and skilled ‘sailors’. A link between the two behaviors suggests the importance of ballooners also being able to sail, which could be advantageous when landing on water.

The authors conclude:

“The ability of individuals capable of long-distance aerial dispersal to survive encounters with water allows them to disperse repeatedly, thereby increasing the pace and spatial scale over which they can spread and subsequently exert an influence on the ecosystems into which they migrate.

The potential for genetic connectivity between populations, which can influence the rate of localized adaptation, thus exists over much larger geographic scales than previously thought. Newly available habitat may be particularly influenced given the degree of ecosystem disturbance that is known to follow new predator introductions.”

Morito Hayashi, Mohammed Bakkali, Alexander Hyde & Sara L. Goodacre
Sail or Sink: Novel behavioural adaptations on water in aerially dispersing species
BMC Evolutionary Biology 2015 doi 10.1186/s12862-015-0402-5

Image shows water tolerance and tiptoeing. The relationship between tiptoeing, sailing and the ability to float on water. All tiptoeing individuals were also sailors, except for two individuals, suggesting that the sailing behaviour is almost completely associated with, and possibly a requirement for, the aeronautic behaviour. Credit: Hayashi et al. by Creative Commons Attribution License