Science Questions

How do spiders make webs?

Sun, 18th Oct 2009

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Question

Charlie, Milton Keynes asked:

How do spiders build their webs? Are they brilliant mathematicians?

Answer

We put this question to Todd Blackledge, Associate Professor of Biology at the University of Akron:

"Surprisingly, despite how elegantly symmetric orb webs are, they don’t have a map of the shape of the web.  Instead, they have genes that control how they move individual legs as their manipulating silk thread and how to interconnect silk threads.  It all starts off with a bridge thread.  Closeup of spiral orb webSo a spider can suspend its web in mid air by releasing a very lightweight silk thread until it snags on something such as a tree on the other side of the trail you're walking on.  That bridge thread then forms the core of the web.  The spider is able to move out and begin to build an outer framework for the web, at the same time as it establishes what are called the radial threads, those you can think of as the spokes on a wagon wheel.  And then once this framework is done, the spider then produces a temporary spiral, so it starts at the centre of its web and this temporary spiral acts as a physical guide for the spider to then spin the final gluey capture spiral.  And the spider starts at the outside of the web, follows that temporary spiral and essentially paints itself into a corner in the centre of its web.  They actually use their legs to measure the distances.  So if you watch an orb spider spinning its web, it’s reaching out with one set of legs to touch the temporary spiral and then using its hinds legs to then position the sticky spiral.  So spacing between rows of silk is going to change as the spider matures and the length of its legs grows longer and longer."

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My understanding is that a spider releases a long, continuous stream of very light thread that wafts away on the breeze. The spider regularly tests the tension on the silk so that it can tell as soon as part of the line snags another remote surface - a twig on a nearby branch for instance. The spider tightens, ties down and then walks across this line, counting its steps so that it "knows" how long it is. Securing the other end it then back-counts steps to what would be the middle of this line and drops a perpendicular to form a T shape, which it attaches to the ground or another object vertically below. This creates the initial scaffold for the web, which the spider then "fills in", again using step-counting to log distance.

The measurement of distance by counting steps is interesting because ants do the same thing to help them find their way around. In 2006 a University of Ulm team found that if ants were given the insect-equivalent of stilts (by gluing on pigs hairs to lengthen their legs) they regularly over-shot their nest locations because the walked too far along all of the "legs" of their journey between food sources and home. The reverse was true when their legs were artificially shortened. This could only be rationalised with the insects using a kind of "neuro-pedometer" to cognitively-count their steps in order to keep track of the distances they were covering.

The Ant Odometer: Stepping on Stilts and Stumps, Matthias Wittlinger, Rüdiger Wehner, Harald Wolf, Science 2006, Vol. 312. no. 5782, pp. 1965 - 1967

Chris chris, Sat, 17th Oct 2009

Q. How do spiders make webs?

A. Badly if they've had too much coffee...



http://www.newscientist.com/article/mg14619750.500 RD, Sun, 18th Oct 2009

I wonder why alcohol and nicotine are not represented? After caffeine they're almost certainly the most sued human drugs...

chris, Sun, 18th Oct 2009

Don't spiders just go online and order them from the world wide web ?  *groan* neilep, Sun, 18th Oct 2009



The effect of alcohol on spiders is mentioned in this youtube video ... http://www.youtube.com/watch?v=sHzdsFiBbFc  RD, Sun, 18th Oct 2009

That's very funny - I especially like the alcohol spider, but the crack spider is pretty cool too! chris, Sun, 18th Oct 2009

Hee hee !!.. crack Spiders bitch !!  neilep, Sun, 18th Oct 2009

After making a T shape I think spiders make the first few circular strands out of a non-sticky thread, then filling in the rest of the web with the sticky prey catching thread.

I think Spiders have an average of 3 spinnerets which can make different types of threads..eg. sticky silk thread, non sticky thread, and fine silk thread for wrapping around caught prey.

The distance between the circular strands is the distance between the spinneret and the back legs I think.

I also have heard that they are not always immune to their own glue and usually leave a non-sticky prey line to allow them to run in to collect their caught prey.

I think they can also eat their own webs if desperate as they are protein based.

A spider web is a thing of real beauty...a spider gives me the creeps, WHY IS THIS? LOL 

More importantly guys, why are so many of us scared of these tiny creatures!

Me personally am a bit freaked out by them.... its those kneecaps  and hairy legs that freak me out every time)

ellie ellieanita, Tue, 20th Oct 2009



There is natural selection for arachnophobia ...


http://www.bmj.com/cgi/content/extract/333/7562/278-a

RD, Tue, 20th Oct 2009

I've got a further question––since not all spiders weave a spiral web (I have a pet Tegenaria Duellica or Giant House Spider that weaves a tunnel web) is this determined by the length of a spiders legs, as well?  In other words, if a spider's legs are too long would spinning a spiral web leave spaces too large to capture its prey?
Thanks!
Paul walkingoliver, Wed, 4th Nov 2009

Urg... of all my Fathers and Mothers creations, he and she had to create that beast. Mr. Scientist, Wed, 18th Nov 2009

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