Inquiring minds want to know what kind of webs spiders build in zero gravity. This is an obvious experiment and it has been done.
Circa 1973, two spiders were sent up to Skylab. Things didn’t work out as hoped. The photographic data collection was inadequate, and in any case the spiders built few and ‘irregular’ webs. Also, there were no provisions for the poor spiders, so it isn’t clear whether the results reflect gravity or the slow starvation of the victims spiders.
In 2008, another two spiders (and some food) were sent to the ISS. Things didn’t work out as hoped, again.
For one thing, the spider that was intended to be a reserve escaped into the observation chamber, where the two spiders made webs that intersected. Worse, their food supply, live flies, multiplied out of control, and soon the larva filled the observation chamber to the point that the webs could not be seen at all. Were the spiders smothered by their own food supply?
And, by the way, one of the spiders only built webs when the light was turned off, dismantling it before ‘dawn’. This natural behavior foiled some of the photographic data collection.
Biology is messy.
The experiment was repeated in 2011 on the ISS [2]. The second experiment showed that it was very difficult to detect anomalies in very symmetrical webs. For that reason, the next subjects were selected from builders of highly asymmetric webs. The idea is that, with no gravity, the spider can’t tell which way is ‘up’, so the web will be more symmetrical, or at least we can tell which way the spider thinks is up.
This 2011 experiment used more cameras, collecting thousands of images over weeks, and finally got some decent results. (There was an identical control on the ground, i.e., with normal gravity.)
Biology is still messy. : – )
In the absence of gravity, the spiders made webs that were more symmetrical—sometimes. It turned out that in ‘night time’, when the light was off, the web was more symmetrical. But in ‘day time’, when the light was on, the web was asymmetrical.
Evidently, in the absence of gravity the spiders could use light as a cue to orientation. (Note that in nature, the spiders generally build webs in the dark–so they normally don’t use light, at least not very much.) Only without gravity and light was the spider unable to orient the web.
Or, put another way, spiders generally orient to gravity, but if that isn’t working, they can use light as a cue to direction.
Who knew!
- University of Basel, Spiders in space: Without gravity, light becomes key to orientation, in ScienceDaily, December 9, 2020. https://www.sciencedaily.com/releases/2020/12/201209115149.htm
- Samuel Zschokke, Stefanie Countryman, and Paula E. Cushing, Spiders in space—orb-web-related behaviour in zero gravity. The Science of Nature, 108 (1):1, 2020/12/03 2020. https://doi.org/10.1007/s00114-020-01708-8
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