It happens in just a few seconds, but the moment wingless crab spiders from Germany take flight, it's majestic and – if you’re arachnophobic – terrifying.
A new study published in PLOS Biology offers never-before-seen detail into not only how “flying” spiders are able to soar through the air, but also what helps them decide the right time to do so.
Researchers conducted a series of field observations in a Berlin park and laboratory experiments in a controlled wind tunnel. In both cases, the 5-millimeter-long Xysticus spider was placed on a dome-like platform. In the video, the spiders are seen tying themselves to the launchpad with an anchor line before doing what appears to be a line-dance from the 1990s. The arachnids activate their spidey senses by raising one or both legs to evaluate wind conditions and orient themselves against the direction it is blowing.
Only when the wind is just right – for a crab spider, that’s under 3 meters per second (7 miles per hour) – do they begin to spin out three lines of “ballooning” fibers. The first two lines scientists have viewed before: These two draglines are made from a fiber measuring on average 700 nanometers in diameter. With a slight updraft, the spider will then rapidly spin between 50 and 60 ballooning fibers made from much thinner silk that measures less than the wavelength of visible light (200 nanometers). This line provides the lift they need to take off.
If all goes to plan, the spider will cut its anchor line at the moment of takeoff. If something happens, such as a slight downdraft or change in wind speed, they will continue to spin out from their anchor line until the conditions are ripe to cut loose and set sail.
If you’ve ever seen Charlotte’s Web, then you know certain species of spiders will take flight to cover hundreds of kilometers after birth to find a new place to call home or in search of prey or a mate. This study gives insight into how they are able to know when it’s go-time.
"The pre-flight behaviors we observed suggest that crab spiders are evaluating meteorological conditions before their takeoff," said study author Moonsung Cho in a statement. "Ballooning is likely not just a random launch into the wind, but one that occurs when conditions most favor a productive journey."