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Spiders need lots of space to show their stuff

September 27, 2015

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Friday (September 25) I was checking the recycling blue bins beside an old three-storey walk-up apartment building in Mount Pleasant. There were returnable beverage containers to collect and I did collect them but I was much more interested in the little European garden spider that was suspended above the three bin set.

There was nothing above the spider but blue sky and one horizontal strand of web that stretched north-south for a good 7 metres (23 feet) at least.

It was the kind of superhuman engineering feat that only a spider with its silk is capable of and one that I’d seen many times before.

What spiders know how to do is amazing but I sometimes wonder if it may all be instinctive. There’s really nothing that I’ve seen that absolutely proves they can learn new things. They certainly don’t seem to learn from their mistakes.

The impressive effort that I was watching, for example, was doomed to failure from the start, by a simple mistake that I see Vancouver’s European garden spiders making over and over again.

Spiders seem clever but are they really?

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Not all species of spiders build webs but each species that does seems to be instinctively hard-wired to build a certain style of web — funnel, tube, sheet or orbs — in a certain way.

The European garden spider that I was watching exclusively builds radial orb webs and it seems to build them using a surprisingly rigid formula.

The single horizontal strand that it had strung between a projecting bit of bush and a dumpster was almost certainly the initial base line that the rest of the web would hang from.

Improbably, given the sheer length of this bridging line, it is said that orb-building spiders always begin by throwing caution to the wind; that is, they rely on the breeze to find an anchor point for the first sticky strand of silk that they spin out.

The recipe to make a radial orb web

Basic orb web construction. -- adapted from NASA

Basic orb web construction. — adapted from NASA

Once the strand does stick and if the spider can traverse it, the length and endpoints are heavily reinforced. Then, at two widely separated points along what is now the base line of the web, the spider fixes an extra-long, non-sticky stand, which describes a loose arc under the baseline (that might’ve been what the spider was doing when I interrupted it).

The next step would be to find the centre of the loose strand (the centre of the orb web) and pull it tight with a sticky vertical strand attached to something below the planned web. The result would be a “Y” shape stretched between the upper base line and the lower anchor point.

Unfortunately for this industrious spider, the only “somethings”to attach the vertical anchor to were the recycling blue bins, which open and close and move without warning.

Vancouver’s European garden spiders appear to know full well that recycling and garbage bins are good places to find flies and such but they don’t seem to be able to learn that they shouldn’t anchor their webs to the lids of recycling blue bins.

It’s the sort of thing that makes me question whether spiders can learn at all.

All “nature” and little or no “nurture”

The tip off to build their webs near garbage may be chemical cues, such as excess methane in the air, that spiders have used for tens of millions of years and, when I look closely, any evidence of ingenuity and creativity that I think I see in web design can be explained by choices forced on spiders by variations in the environment where they have chosen to build their web.

Spiders might be almost be flippantly compared to smartphones. They come equipped with a bunch of hardware functions, similar to the camera, accelerometer and gyroscope that you get in a current smartphone, plus they come with specialized sensors to measure such things as tension and the pull of gravity.

The web-building apps that would come with these arachnid “smartphones” — that would be burned into their firmware, as it were — might not need to as powerful and sophisticated as a person might think.

That is to say that the spiders I see in Vancouver could be said to resemble so-called expert systems — computer programs designed to emulate the decision-making of experts.

If I’m implying that spiders do not seem truly intelligent, it isn’t actually to belittle the ones that I see around me. Their behaviour is endlessly fascinating to watch and the complete package that a spider presents, including the amazing silk web that only a spider can make, is one of the great success stories of evolution — orb-weaving spiders, not unlike what we have today, existed 200 million years ago in the Jurassic period!

Now, against my notion that spiders are, shall we say, rather fixed in their ways, I will present the example of Arabella and Anita, two spiders drafted into the U.S. space program in the 1970s.

What a tangled web they weave in outer space…at first

Arabella's first web aboard Skylab 3. -- NASA, JSC-SL3-110-1452

Arabella’s first web aboard Skylab 3. — NASA, JSC-SL3-110-1452

In an experiment suggested by high school student Judith Miles of Lexington, Massachusetts, the two female European garden spiders were included in the payload of Skylab 3, launched on July 28, 1973.

Spiders understood how to built their webs in Earth’s gravity but how, Judith Miles wondered, would they do in the zero gravity of Earth orbit?

The answer was terribly…at first, but both spiders were able to adapt perfectly with only a few days of practice.

Arabella’s first tentative web, spun on August 5, was sloppy and loose but by August 21st she had mastered weightless web-making and that day her last web in space reportedly the best anyone had seen her make, weightless or otherwise.

At that point Arabella was returned to her launch vial and Anita was set to web-weaving.

Like Arabella, Anita balked at first but was quick to adapt to the alien conditions.

The original experiment only called for each spider to produce three webs and the plan was to let the spiders subsist on the nutrition of one fly and some water provider before lift-off and another dead fly and some more water left in their space habitat — with the full expectation that they would die long before the end of the mission.

However, two days into the experiment with Arabella, Scientist Pilot Owen Garriott requested and was granted a change in protocol. From then on, the the two spiders were fed from the crew’s supply of filet mignon, and provided with additional water, with a goal bringing them back to earth alive, with samples of their webs.

However, Anita died unexpectedly about 45 days into the 59 day mission and upon the return to Earth Arabella was also found to have died. Autopsies showed both spiders had died from dehydration.

Their orbital orb webs showed unique variations in thread thickness not present in their earthbound webs, indicating that both spiders had deliberately changed how they extruded their silk in order to compensate for the lack of gravity and achieve the necessary tension.

Also, the zero gravity webs were found to be woven of much thinner silk overall, giving positive evidence that the spiders utilized a weight-sensing faculty to size their thread. Click the images to enlarge them.

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