Scientists figure out the step-by-step process involved when the spiders float in the wind in search for food or for a new home.
Many spiders, big or small, engaged in a behavior called "ballooning" where they tend to fly on the wind for hundreds of kilometers to search for a mate or find another place to colonize. While ballooning has been a subject of numerous scientific studies before, the current study dissected how exactly the spiders take off from their point of origin.
The study, conducted by Moonsung Cho, an aerodynamics engineer from the Technical University of Berlin, found that spiders actually strategize before "flying." They can even determine the condition of the wind favorable for the activity.
The study is said to be the first detailed analysis of ballooning. In the future, their insights could help aerodynamics experts in designing important flying devices.
Spiders Float In The Wind
To conduct the experiment, Cho and his team collected crab spiders and observed them in a Berlin park, and in a laboratory set up. Crab spiders are about 5 millimeters long or about 0.11 inches and weigh up to 25 milligrams.
The study, published in the journal PLoS Biology on June 14, found that spiders would first sense the wind by raising one or both of their front legs. The arachnids would repeatedly raise their legs to evaluate the condition and direction of the wind.
"The pre-flight behaviors we observed suggest that crab spiders are evaluating meteorological conditions before their takeoff," explained Cho.
When spiders sensed that the wind speed is less than 7 miles per hour, they would then release multiple nanoscale fiber silks that measure about 10 feet long. Before they fly away, they would first leave some strands of the silk anchored to the ground, or to the blades of grass which served as their launching pad. The spiders would then launch themselves to the wind using the remaining strands of the silks.
The team concluded that spiders do not spin their silk aimlessly during ballooning. Instead, the process of floating or flying among spiders involves complicated strategizing mechanism.
Thinner Than Light
In the laboratory, the team observed that one spider could release up to 60 fibers, and most of the silks were as thin as 200 nanometers. Upon closer inspection, with the help of an electron microscope, Cho found that these silks are thinner than the wavelength of visible light.
"Most winged insects flap their wings to build a vortex of air to lift their bodies and make them float," Cho explained. In the case of crab spiders, their nanoscale silks were so thin that they instead make use of the density of air to stay floating in the wind.