Sunday, 9 October 2011

Ballooning With the Stegodyphus Spider

There are 21 different species of the Stegodyphus. Most are found in Africa, Europe and Asia. There are a few species that have made their way to Brazil. Not all species of Stegodyphus use ballooning as a form of dispersal.
These creatures are very small with an average length of only 10mm, and an average weight of only 85 to 150mg. This small mass and body size are the reason that it is able to be carried away by the wind. This type of transportation obviously has a very small mass limit. The spider lets out 3 to 4 strands of thread to induce this floating transportation, each a length of about 60 to 80 centimeters for an overall length of 1.8 to 3.2 meters. The original study states that they can reach altitudes of over 1000 meters above the ground.
The most recent study has shown that the Stegodyphus is able to gain altitude after releasing many strands of silk. These fan out to create a large surface area, which enables larger or more massive spiders to disperse as well. Although they have no ability to maneuver while in the air it is impressive that they have found such a unique way to disperse themselves. This technique obviously works well, because they have spanned to four different continents.

 In the first one you can see how they raise their tails to begin releasing the thread. In the second photo if you look closely behind its tail you can see some of the thread.
The new study points out that the 20-year-old model for spider "ballooning"—which assumed that spider silk is rigid and straight and spiders just hang at the bottom—was flawed when applied in moving, turbulent air.
When a spider wants to travel long distances, it simply casts out a strand of silk, captures the breeze and "flies" away. They are known to travel hundreds of miles, even ending up on islands in the middle of the ocean
Researchers at Rothamsted Research redesigned the model to allow for elasticity and flexibility in the spider's dragline, its most sturdy line of silk used for moving about and snagging prey. When the dragline is caught in a turbulent breeze, it becomes highly contorted, catching air like an open parachute and sending the spider on an unknown journey.
Now scientists have figured out how this mode of transportation works. They also discovered that spiders have very little influence where they're flown when caught in a stiff wind. 
The spider has virtually no control of where or how far it travels by this means, said Andy Reynolds, a Rothamsted Research scientist. This is how a "ballooning" spider can end up in the ocean hundreds of miles from shore.
In more calm breezes, though, spiders can drift just a few yards to invade new territory orsurprise prey.
Although the new model better illustrates how spiders "fly," there is still room for refinement, and the team plans to observe spiders in turbulent airflow inside wind tunnels to improve the model. Better understanding how spiders travel long distances could help scientists control farmland pests.
"Spiders are key predators of insects and can alleviate the need for farmers to spray large quantities of pesticide," Reynolds said. "But they can only perform this function in the ecosystem if they arrive at the right time. With our mathematical model we can start to examine how human activity, such as farming, affects the dispersal of spider populations."

No comments:

Post a Comment