Spiders have sailing abilities that may match Spider-Man's ability to get from point A to point B. A new study explains how terrestrial spiders can move from one place to another to create a more conducive habitat, even when bodies of water are encountered along the way.
The researchers describe how the physical features of the spiders used in the study are able to help them migrate to new places.
Common spiders set themselves high in the air through a movement technique called "ballooning," which pertains to the usage of their silk to get help from the wind and propel themselves up into the air.
On the average, ballooning enables spiders to move by up to 30 kilometers (approx. 19 miles) per day, provided that the wind conditions are fitting. However, spiders have minimal control over the places where they will end up, facing the possibility of landing on water, which is said to be an incompatible place for spiders to thrive in.
The study, published in the open access journal BMC Evolutionary Biology, involved 21 species of spiders found in the nature reserves in Nottinghamshire, UK. The study subjects, totaling to 325 adult spiders with water-repellent legs, were placed on trays of water where pump-generated air was induced and subsequently observed.
The spiders were also placed on dry surfaces for comparison. The researchers observed the spiders for six individual behaviors and six combined behaviors: sailing, upsidedown sailing, anchoring, walking/moving legs and death mimicry. Through these behaviors, the researchers were able to observe how exactly the spiders use their bodies in relation to long-distance migration, with bodies of water along the way.
When spiders come in contact with the water, they raise their legs to serve as sails, thereby allowing them to cruise along the water smoothly and to subtly slide across the surface without a turbulent aftermath.
Sailing is said to be an exclusive response to water as majority of the spider subjects walked with bent legs to fight the wind on dry surfaces. During upsidedown sailing, the spiders cleverly raise their abdomen, exhibiting a posture comparable to a handstand. They then slide on the water in response to the wind.
Spider silk is released onto the water surface, decelerating the movement of the spider, or halting it against the dominant wind. In instances when the silk gets in contact with a floating material, the spider walks toward that material using the silk as its walking medium. When walking, the spider moves its legs so swiftly and often in a downwind trend.
Spiders were also observed to stay motionless for seconds, a technique known as death mimicry. This action is said to help the spiders avoid potential predators from attacking.
In the end, researchers Morito Hayashi from the Natural History Museum in London, Mohammed Bakkali from the Universidad de Granada in Spain, Alexander Hyde, a British professional wildlife photographer and Sara Goodacre from the University of Nottingham discovered that the legs of the spiders serve as sails and their silk as anchors.
The disposition to sail is likely associated with the tendency for aerial dispersal and potentially because sailing may minimize the consequences of landing on water. As spiders can thrive even without food for a long time, those trapped in water may survive long enough until they find a distant, potential habitat.
Photo: Aleksey Gnilenkov | Flickr
