On earth, they weave their filigree wheel nets according to ingenious rules – but to what extent can spinning also succeed in the weightlessness of the ISS space station? Experiments show that the eight-legged astronauts can manage without gravity. However, researchers report that their networks in space have an interesting peculiarity: they are more symmetrical than on Earth – but only if they were tied in the dark. According to the scientists, the spiders orient themselves towards the light when they cannot rely on gravity when building a web.
They seem to be floating – but on earth, of course, their transparent threads give the orb web spiders the necessary support. It is known that their behavior and web construction also have to do with above and below: The webs of orb web spiders are spun a little more far-reaching in the lower area than above. As a result of this asymmetry, the center of the structure is also shifted towards the upper edge. There the spiders sit in a resting position and wait for a trapped insect to vibrate the threads. In doing so, they also align their body position sensibly: They lurk upside down because they can get to their prey faster in the direction of gravity.
Clever in space too
But how do spiders react to weightlessness in space? This was investigated a few years ago on the International Space Station. Basically, it was shown that the orb-web spiders of the species Trichonephila clavipes do not fall into irritated apathy under the unusual circumstances: They skillfully built their nets in the test containers even without the influence of gravity. Scientists working with Samuel Zschokke from the University of Basel are now reporting interesting details of these observations. They are based on the exact evaluations of the recordings of the astro networks in comparison to the terrestrial versions.
It turned out that the nets built in weightlessness were proportionally more symmetrical than those spun on earth – their center was therefore more towards the middle. In addition, the spiders did not point their heads in a certain direction when they were in wait. But as the scientists report, this was only true under one condition: if the spiders were kept in the dark. In the lamplight, on the other hand, the test animals built their nets on board the ISS as asymmetrically as on earth. They also turned their heads away from the direction of the light when they were at rest.
Light as an orientation aid in network construction
“We would not have suspected that light plays a role in the orientation of the spiders in space,” says Zschokke. “We were very lucky that the lights were on top of the chamber and not on different sides. Otherwise we would not have been able to determine the effect of light on the symmetry of the nets in weightlessness, ”said the scientist. The results show that spiders use light as a guide in addition to gravity. Since spiders can also build their webs in the dark and catch prey without light, it was previously assumed that light plays no role in the animals’ orientation.
“The fact that spiders have such a reserve system for orientation seems surprising, since in the course of their evolution they have never been exposed to an environment without gravity,” says Zschokke. According to him, there is a plausible explanation: The additional source of information could help the animals not to get confused. Because during the construction of their networks, they sometimes move so intensely that an additional orientation aid based on the direction of the light can be useful, explains the researcher.
Source: University of Basel, specialist article: Science of Nature, doi: 10.1007 / s00114-020-01708-8
Video: Recordings of an orb web spider building its web on the ISS.
(Credit: BioServe Space Technologies)