Sometimes spiders ride the wind. They spin out lines of silk that are caught by the breeze and carry them aloft. They have been reported to rise a mile or two above the earth, and perhaps even to cross oceans.
It is called ballooning.
Moonsung Cho, an aeronautical engineer, was in Australia the first time he saw the flight of a spider. It was autumn, when baby spiders often balloon en masse and spread to new areas.
He was completely taken by the phenomenon and made it the subject of his studies toward a doctorate at the Technical University of Berlin.
The flights of spiders are well known, but not their physics, so Cho tested crab spiders in nature and in a wind tunnel, and discovered, among other things, what holds the spiders up in the air.
They do not actually have balloons, but rather numerous strands of silk that they spin up to 6 feet long. And those threads of silk, from 100 to a few hundred nanometers wide (a human hair is just under 100 nanometers in diameter), are so thin and lightweight that they are suspended in the air like a thread, or a hair, in molasses.
Compared with a silk thread, the air is like a thick fluid, so the effect of gravity is easily counteracted by what you might call the stickiness of the air. In a breeze, the flowing air carries the silk threads along with it, as the spider rides beneath.
Cho and his colleagues also reported that the spiders actually test the wind, raising a foreleg to judge how strong it is. They prefer a mild breeze, about 7 mph.
Beyond pure physics, Cho has learned a great deal from them in the five years he has been studying them. Spider flight has been known for the longest time, he said, but still had secrets to yield.
It may seem that nature has been fully explored by science, but "we need to change our viewpoint," he said. "There are a lot of things which we don't know."
ActiveStyle on 07/09/2018