Spiders are capable of building typical webs in microgravity, so long as they have access to a light source, according to new research published in Science of Nature. In the absence of gravity, and hence a sense of up and down, a light source provides a frame of reference for the spiders. When a light source is available, spiders will weave their normal asymmetric webs and wait near the top for prey. Without light, however, they build symmetrical webs, which isn’t normal behavior. It’s a surprising discovery, highlighting the relative unimportance of gravity for spiders when weaving their webs.
Under normal gravity conditions, orb web spiders tend to build asymmetrical webs with the center, or hub, positioned toward the upper edge. When resting and waiting for prey, spiders sit in their hub with their heads facing downward, allowing them to quickly pounce on their prey in the direction of gravity.
Because of this, scientists figured that spiders would be thrown off kilter when exposed to microgravity. Experiments done in 2008 aboard the ISS affirmed these suspicions, revealing the symmetrical web construction. That said, the 2008 experiments were somewhat of a fiasco, as a spider was accidentally released into a habitat occupied by another spider, which created total chaos and a mishmash of competing webs. What’s more, the growth of fruit fly larvae (which were used to feed the spiders) got out of hand, making it next to impossible for the researchers to see the webs through the viewing window. The experiment was tainted, but scientists did catch a glimpse of those weirdly symmetrical webs.
“When the opportunity arose to do another experiment in 2011, we decided—based on the…conclusions from the 2008 experiment—to use spiders which build highly asymmetric webs under normal gravitational conditions…to detect a difference in web shape between webs built in zero gravity and the control webs,” write the authors in the new study, led by Paula Cushing of the Denver Museum of Nature and Science and Samuel Zschokke from the University of Basel.
The chosen species for the 2011 spider experiment is the golden silk orb weaver, or Trichonephila clavipes. Cushing and Zschokke designed an experiment in which two spiders would build their webs in separate testing chambers on the ISS, while two spiders were kept in identical habitats on the ground to serve as the control group. They also changed up the whole fruit fly larvae thing to prevent the shenanigans seen in 2008.
The researchers documented the spiders’ web-building behavior over a period of two months using cameras that took photos once every five minutes. In total, “we assessed the spider orientation in 100 webs based on 14,528 pictures, of which 14,021 showed the spider in its resting position and could therefore be used for the analysis,” write the authors.
It turns out that the spiders, when working in microgravity, tend to weave webs that are discernibly more symmetrical than those built on Earth. Also, the hubs were positioned closer to the center of the webs, and the spiders didn’t always keep their heads in a downward position.
But this wasn’t the case across the board. Some webs exhibited a surprising degree of asymmetry, especially for those “whose building had started when the lights were on, suggesting that light replaced gravity as an orientation guide during web building,” according to the paper. Moreover, the light also provided a reference for the spider in terms of positioning themselves atop the web (by top, the researchers are referring to the top of the habitat ).
Funny thing is, access to a light source was not even considered as a factor going into the experiment.
“We wouldn’t have guessed that light would play a role in orienting the spiders in space,” said Zschokke in a University of Basel statement. “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.”
Happy accidents are so great, particularly when they lead to new scientific findings. But that’s why we call them “experiments,” as we wouldn’t be doing these things if we knew the outcomes in advance.
source: Gizmodo.com by George Dvorsky