Who Knew? Light Is the Key to Spiders Weaving Webs in Space

Spider building an asymmetric web in zero gravity
BioServe Space Technologies, University of Colorado Boulder

I’m willing to bet a lot of people (including myself) are terrified of spiders. But that doesn’t mean they’re not interesting. In a two-month study led by Paula Cushing of the Denver Museum of Nature and Science and Samuel Zschokke from the University of Basel at the International Space station, scientists found that Trichonephila clavipes spiders used lights as a substitute for gravity when placed in outer space as a way to not only orient and position themselves but weave their webs.

The duo used three cameras that were set up to take a picture every 5 minutes. They had two spiders on Earth, and two “arachnauts” up in outer space. Each was enclosed in their own case, in a controlled habitat. In total, they shot 14,528 photos. The scientists were able to use 14,021 of them as it showed the spiders in their resting position.

Normally, they build their webs asymmetrically, with their hubs near the top. The hub is a place where a spider hangs out while waiting for prey to trip the web. They usually face downwards, in the direction of gravity, until prey arrives.

But Cushing and Zschokke found that while in zero gravity, a light source was a key factor in the way spiders were weaving their webs. When present, the spiders built their webs similarly to how they would down on Earth (asymmetrically) with their hubs on top.

Where things got interesting is when scientists turned off the lights. In this environment, the spiders consistently weaved symmetric webs with no preference when it came to orientation, and their hubs were typically closer to the center. On Earth, the spiders tend to face downward while waiting for prey. In space, things went differently. Without light, spiders were much less likely to face downward. But leaving the lights on when the spiders weaved webs led to them facing downward more consistently. The spiders also had no reaction to the change in lighting for up to an hour, maintaining orientation they had chosen.

This lead Zschokke and Cushing to conclude that the spiders use light as a substitute to decide their orientation when there was no gravity. The eight-legged creatures also used light as a way to move closer to the top of the web. The researchers hadn’t even considered light when starting the experiment.

Spider building a symmetric web in zero gravity
BioServe Space Technologies, University of Colorado Boulder

Zschokke said, “We wouldn’t have guessed that light would play a role in orienting the spiders in space.” He cited that, “We were very fortunate that the lamps were attached at the top of the chamber and not on various sides. Otherwise, we would not have been able to discover the effect of light on the symmetry of webs in zero gravity.”

It’s stunning that the spiders were able to adjust themselves to the lack of gravity. Even Zschokke was shocked, saying, “That spiders have a back-up system for orientation like this seems surprising, since they have never been exposed to an environment without gravity in the course of their evolution.”

But not everything went according to plan. For example, they had planned to have four female spiders for the experiment. They were chosen as juveniles and as it turns out, they discovered two of them were males. Scientist wanted to control for sex, because a spider’s body structure and size are different, depending on its gender once they’ve become fully grown. The good news is that only one of the males made it on the ISS, while the other one remained on Earth.

Putting anything into outer space is always interesting. The fact that spiders were able to instantly adapt to the lack of gravity is absolutely mind blowing. It makes me curious how other animals may react in the great unknown.

Source: University of Basel via Gizmodo