Spiders in Space Rely on Light for Orientation

Humans have taken spiders into space more than once to study the importance of gravity to their web-building. A new study—led by researchers at the University of Colorado’s Bioserve space Technologies, and published in Science of Nature—describes how the webs built in zero gravity were more symmetrical than those spun on Earth, and the arachnids rely on light to orient themselves. 

The experiment started with four spiders of the same species (Trichonephila clavipes): two flew to the ISS in separate habitats, two stayed on Earth in separate habitats and were kept and observed under identical conditions as their fellows traveling in space—except that they were exposed to terrestrial gravity.

The arachnids spun their webs, dismantled them, and spun new ones. Three cameras in each case took pictures every five minutes. It turned out that the webs built in zero gravity were indeed more symmetrical than those spun on Earth. Their center was closer to the middle and the spiders did not always keep their heads downwards. However, the researchers noticed that it made a difference whether the spiders build their webs in lamplight or in the dark. Webs built on the ISS in lamplight were similarly asymmetrical as the terrestrial webs.

"We wouldn't have guessed that light would play a role in orienting the spiders in space," says researcher Samuel Zschokke. "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."

Analysis of the pictures also showed that the spiders rested in arbitrary orientations in their webs when the lights were turned off, but oriented themselves away—i.e. downwards—when the lights were on. It seems spiders use light as an additional orientation aid when gravity is absent. Since spiders also build their webs in the dark and can catch prey without light, it had previously been assumed that light plays no role in their orientation.