If you think space is tough on astronauts, you should try being a spider spinning a web in pitch black microgravity. OK, so that sentence is kind of a non sequitur, but it accurately describes a fascinating, somewhat oddball science experiment carried out aboard the International Space Station (ISS).
You see, spiders on Earth are pretty darn good at spinning webs. Gravity, it turns out, is a key part of the way spiders orient themselves on webs. Spiders typically begin spinning their webs by dropping down from above and attaching anchor lines. The spider then typically sits on the upper-third of the web, facing down, waiting for prey.
Scientists know just what a big deal gravity is to spiders because they have carried out what sound like incredibly annoying (to a spider, at least) lab experiments in which spiders are allowed to start spinning a web on a frame before the researchers invert the frame on a horizontal axis in order to see how the arachnid reacts.
But what happens if you remove Earth levels of gravity altogether? This was what an international team of scientists set out to test when they rocketed two spiders of the same species (Trichonephila clavipes) to the ISS to see how they would cope when spinning webs in zero gravity.
“What we found is that if a spider in space has no clue from gravity and no light, so that it has no idea what’s up and down, they’ll face in any random direction when they sit on the web,” Samuel Zschokke, a research fellow at the University of Basel in Switzerland, whose main research interest is spider webs, told Digital Trends. “As a result, the web is no longer asymmetric, it’s pretty much symmetric.”
Seeing the light
Asymmetrical webs are a common feature of spider webs on Earth. Webs exhibit an up-down size asymmetry so that the lower part of the web capture area is bigger than the upper. Unsurprisingly, without any gravitational guide, this doesn’t occur. Spiders will still spin webs, but they don’t look like the ones on Earth.
However, Zschokke said that when the spiders were given a light source, they substituted this for gravity using the light as a proxy to build toward it in the same way they would normally head toward the pull of gravity. Zschokke said that this ability on the part of spiders to reconfigure their behavior is fascinating because, on Earth, they require no light to build webs. In essence, they swapped out one sensory reaction (if gravity counts as a sensory reaction) for another.
“They have this way of compensating for the loss of gravity by using light,” he said. “That’s something we did not expect. Because why should any animal which has always lived in a gravity environment like Earth be able to compensate for a lack of gravity with something else?”
Collaborator Stefanie Countryman, director of BioServe Space Technologies and an aerospace engineering research associate at the University of Colorado Boulder, told Digital Trends that the results of the study provide valuable information on how living organisms can adapt to a zero-gravity environment.
“With more and more interest in long-term space exploration and living off-planet, studies like these can help inform how to keep living organisms healthy in space and how they might adapt to space,” Countryman said. “The next steps would be to repeat the experiment, but with larger habitats that are large enough for this particular type of spider to build a web that is closer in size to the ‘normal’ size that would be spun on Earth. It would also be of interest to examine more in-depth how the light cues the spider’s behavior in the absence of gravity.”
A paper describing the research was recently published in the journal The Science of Nature.
