Of course, not all spiders spin webs – but anyone who has accidentally walked into one of the masses of gossamer strands built by one that does, will be able to testify that they are definitely sticky – and the hapless moths, flies and other victims caught in those webs never seem to stand a chance of getting free again (not surprising since spider silk has a relative tensile strength comparable to steel and can be nearly as elastic as rubber). Yet the spider herself can step nimbly from thread to thread without ever seeming to have the slightest tendency to stick at all … so how does she do it?
There have been many suggestions over the years, from careful grooming (although quite how that helps is never really explained) and only stepping on “dry”(non-sticky) threads to tip-toeing carefully around her domain and even having a non-stick coating on her legs! Of course, the spider’s victims usually fly full tilt into the web and get their whole bodies in contact and stuck immediately, while our lady spider only touches the web with tiny feet, probably helps a great deal … after all, those feet present only a minuscule surface area, comparative to her size and strength when it comes to pulling said feet free, while most of the victim’s surface area is already stuck fast.
Recently, however, Briceno, working in a collaboration between the Smithsonian Tropical Research Institute and the University of Costa Rica, proposed a new theory which has been published in the science journal ScienceDaily.com. They managed to film two specific species of tropical spider, Nephila clavipes and Gasteracantha cancriformis, in action at a microscopic level, and they now believe that spiders use a combination of three “anti-adhesion tactics” to keep themselves free of their own traps.
First, the spider’s legs are covered in hundreds of minuscule branched hairs (setae) that decrease the total surface area the web can stick to; second, she uses a careful walking technique with rapid tapping movements that minimizes contact with the glue, reducing the “pull” against the thread and allowing strands to slip away easily. Third, it turns out that the legs are covered in a special chemical that stops the web’s glue from sticking! First indications of this came when they realised that when the spider is creating a web, producing the stickiest threads and pushing them into place with her hind legs without having any problems with unwanted sticking, and it was further confirmed when the scientists washed the spider legs with hexane and water to remove the coating and the legs suddenly began to stick much more afterward.
It is hoped that by studying and perhaps collecting/replicating this nonstick substance used by the spiders, ways of using it to improve current nonstick surfaces for human use may be found.
