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Shedding Light on Spiders in Space

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Humans have taken spiders into space more than once to study the importance of gravity to their web-building. What originally began as a somewhat unsuccessful PR experiment for high school students has yielded the surprising insight that light plays a larger role in arachnid orientation than previously thought.

The spider experiment by the US space agency NASA is a lesson in the frustrating failures and happy accidents that sometimes lead to unexpected research findings. The question was relatively simple: on Earth, spiders build asymmetrical webs with the center displaced towards the upper edge. When resting, spiders sit with their head downwards because they can move towards freshly caught prey faster in the direction of gravity.

But what do arachnids do in zero gravity? The first time spiders were brought into space was in July 1973, when two European Garden Spiders were brought to Skylab to observe their web building. Both spiders built several webs, but the web structure could not be comprehensively evaluated, since there were no photographs showing the entire web.

In 2008, spiders were again brought into space to build orb webs. But this time, photographing the resulting webs was better planned and the spider husbandry was much improved by bringing along fruit fly colonies to provide a continuous food supply for the spiders. In the first days after launch, the spiders moved around in the observation chamber, resulting in it being filled with seemingly random silk strands.

When the opportunity arose to do another experiment in 2011, it was decided—based on the conclusions from the 2008 experiment—to use spiders which build highly asymmetric webs under normal gravitational conditions in order to try and detect a difference in web shape between webs built in zero gravity and the control webs.

All spiders established themselves in their habitat and built their first web within 48 hours of their release into the observation chamber. In general, webs were built around the time at which the lights were turned on and were removed around the time the lights were turned off 12 hours later.

The normal orientation of spiders waiting for prey in normal gravity is always oriented with the spider downwards, but on their web in zero gravity, it was quite variable. Closer analysis revealed that spiders in zero gravity tended to orient themselves downwards when the lights were on, but showed no tendency to face in any particular direction when the lights were off.  It is noteworthy that the spiders remained in the same position for as long as one hour after the lights had been turned on or off, respectively. These results strongly suggest that the spiders use the direction of light as a guiding cue when there is no gravity.

Closer analysis revealed that all webs built in zero gravity, where the web building had started at night before the lights had been turned on, were quite symmetric. However, those webs which had been started during the day, after the lights had been turned on, were quite asymmetric.

In normal gravity, and no matter whether the lights were on or not, spiders consistently built asymmetric webs and consistently faced downwards when sitting on the hub. So it is safe to say that gravity is the most relevant orientation guide for spiders. But based on the observations of these experiments, it can further be assumed that the visual stimulus of the direction of light can serve as an orientation guide in the absence of gravity. It may seem surprising that spiders, even though they and their ancestors had never experienced an environment without gravity, are able to use light as a substitute for gravity for web orientation.

If spiders are causing an issue in your inner space, consult a pest control professional to enlighten you and offer a solution.

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