How do spiders build webs in zero gravity?
Humans have taken spiders into space more than once to study the importance of gravity to their web building and prey capture behaviors. Orb weaving spiders in the family Araneidae have been sent to space on several occasions. On earth, orb weaving spiders rely on gravity cues and wind currents to construct their webs and to position themselves in the silken orb. A spider initiates web construction by releasing a droplet of silk from the abdomen, the droplet is pulled from the spider’s body by air currents and tangles in a nearby object, then the spider utilizes this initial “bridge line” to construct the radial threads and the spiral prey-capture threads of the web.
Dr. Paula Cushing and Stephanie Countryman of Bioserve Space Technologies in Boulder sent orb weavers into the International Space Station in both 2008 and 2011 to learn more about how webs are built in zero gravity. One of the unique challenges was building a habitat that allowed spiders access to food and water while also providing an unobstructed view of the webs.
In both 2008 and 2011 two orb weavers were sent to the International Space Station while two control weavers built webs on earth. Cameras took pictures of the habitats and colleagues Samuel Zschokke of the University of Basel, Countryman and Cushing analyzed the symmetry of webs and the orientation of spiders. The results were published in 2021 in the journal Science of Nature.
One intriguing discovery was that it made a difference whether the spiders began building their webs when lights set in the top of the habitat were on or when the lights were off and the habitat was dark. If the spiders began building their webs during the dark cycle of the experiment, the webs were more symmetrical and the spiders rested in random orientations in the webs. If web construction began when the lights were on, the webs were as asymmetrical as the terrestrial webs and the spiders tended to orient facing down.
Paula E. Cushing, PhD
Senior Curator of Invertebrate Zoology