Spiders and Webs

You might find this interesting...

"This is an arachnophobe's worst nightmare: the largest spider web in the world. It belongs to the Darwin's bark spider, which spins its gargantuan trap over entire rivers and lakes. Its shape - a simple 'orb web' - is normal enough, but its size is anything but. The main anchor thread that holds the web in place to both riverbanks can be as long as 25 metres and the main sticky core can be as large as 2.8 square metres.

With a web that big, it's no surprise that Darwin's bark spider uses the toughest silk of any species. It can resist twice as much force as any other spider silk before rupturing, and over 10 times more than a similarly sized piece of Kevlar. It's not just the apex of spider silk - it's the toughest biological material ever found.

Ingi Agnarsson from the University of Puerto Rico first discovered Darwin's bark spider (Caerostris darwini) in 2001, when he was still a graduate student. While travelling through Madagascar's Ranamofana National Park, he found the giant webs crisscrossing streams and rivers. His initial reaction was a simple "Wow!". "We knew we had found something special and wanted to return to Madagascar to research them," he says. He did so in 2008 and 2010, capturing live spiders, measuring the webs, and analysing their extraordinary silk with spider specialist Todd Blackledge.

Agnarsson found that the silk of Darwin's bark spider is twice as elastic as any other spider silk. This, combined with its high strength, allows it to absorb huge amounts of energy without cracking, the very definition of toughness. For technically minded readers, the fibres resisted an average of 350 MJ/m³ before rupturing, and some threads withstood 520 MJ/m³. For everyone else, these values are more than 10 times tougher than Kevlar. They're so large that Agnarsson makes a special point of saying that he didn't screw up his measurements! He worked with a team of experienced spider scientists, and each of six captured spiders produced silk of comparable toughness."....

http://blogs.discovermagazine.com/notrocketscience/2010/09/16/a-spider-web-that-spans-rivers-made-from-the-world%E2%80%99s-toughest-biological-material/

One year we had an abundance of Argiope spiders - large, colourful orb weavers. They were everywhere that year. One, in particular, wove an especially large web between the corner of the house and the top of the picket fence that ran along the driveway. I stopped to admire her web and just at that moment a fly ran smack into it. The fly was stuck and buzzed loudly as it struggled to get free. Meanwhile Ms. Agriope rushed over to the spot at lightning speed from her 'hiding' place in the centre of the web. She quickly wrapped the fly in silk. Within seconds it was completely immobilized. When she was satisfied with her work, she felt around a bit for the right spot and then sunk her fangs into the bugger. The fly's buzzing, already faint from being wrapped tightly in silk, soon faded to nothing and that was that. The fly's buzzing gave me an idea, however. I went to my shop and got to work.

The 'fly emulator' was a simple affair and consisted of a 555 oscillator set to about the same pitch as that hapless fly's buzz, a 3" loudspeaker with a short length (about 6") of bare solid copper wire epoxy-glued at one end to it's centre, and a 9-Volt battery. The wire stuck straight out from the centre of the loudspeaker. The idea was to make the free end of the wire vibrate much as did that fly when trapped. I waited a few days to let Ms. Agriope finish her meal - and for the epoxy to fully cure. When all was ready, I took the device outside.

Ms. Argiope was parked in centre of the web as usual, her eight legs paired off in the shape of an 'X' behind a pattern of zig-zags - camouflage? Little did she know that her next 'meal' would be a counterfeit. I switched on the power and touched the free end of the vibrating wire to the orb.

Ms. Agriope rushed like gangbusters over to the spot and furiously tried to wrap the end of the wire in silk. I was flattered! Evidently my little machine was indistinguishable from the Real Thing! That, or she wasn't one bit picky (I'd rather believe the former). I withdrew the wire and touched it to another part of the orb. She didn't rush right away this time, but instead touched her feet at different points on the orb as if trying to decipher the 'fly's' location. When she was satisfied that she had, she rushed over to the spot with deadly accuracy and furiously began to wrap the wire in silk as before.

I moved the wire again, this time to one of the web's "anchor cables." She didn't move. Touched a different anchor cable. Nope. Touched the wire to other points not on the orb proper. She didn't budge. When I touched a spot on the orb, it was gangbusters all over again.

I'm guessing the anchor cables distributed the vibrations in such a way as to muddle any directional information that might help her locate the source. In contrast, the orb distributed the vibrations in such a way that she could triangulate the location using the relative phases. That's my guess. She didn't even try if I touched any other part of the web. Just the orb. The petroleum jelly coating on the wire kept it from sticking to her web. Without that coating pulling the wire away would destroy her work and ruin the experiment.

In a day or so another fly had found its way to Ms. Argiope's home. A real one this time, and not some nasty poser powered by Signetics®.