Among the team's findings is that stiffness of a web is not uniform, but varies among isolated fibers, intersection points, and glue spots. For a structure formed supposedly of uniform spider silk, this was a bit of a surprise.
Evolutionarily, the researchers theorize this variation is advantageous to the spider in creating webs that are stiffer in some locations and more elastic in others. They think this might help the web withstand the elements and to better absorb the energy of captured prey.
Another surprise came when Koski looked at supercontraction. In high humiditywhen it rains or in the morning dewspider silk absorbs water, causing unrestrained fibers to shrink by as much as half, likely due to molecular disorganization caused by the water. It a curious response for something so key to a spider's survivability and it has raised some debate in the scientific community as to why nature would have favored supercontraction.
Scientists have posited three explanations for supercontraction. First, some think it is a mechanical constraint inherent in the molecular structure of silk, not an evolutionarily evolved phenomenon and that it has no bearing on the performance of a web. It's just a fact of spider silk. The second theory is that supercontraction helps the spider tailor the silk as it is being spun to meet varying environmental and structural requirements. Or, lastly, that supercontraction helps tighten the web when it gets wet, preventing the heavy water droplets from dragging the web down and preventing the spider from catching any prey.
Until this paper, the last theory could not be tested because researchers had no way to probe complete webs. With their clever technique, Koski and team were able to measure the elastic response of silk during supercontraction. They found that the silk, which is
|Contact: Andrew Myers|
Stanford School of Engineering