This crab spider is not just scuttling around. It is thinking about flying. Once on top of this artificial dome, it raises a leg to sample the airflow. Once it’s satisfied, it raises its abdomen, turns on its spinnerets — the silk-making organs — and shoots threads skyward until it launches. It’s called ballooning, but the spiders hang only from their own silk threads. Incredibly, these spiders are known to ride the wind across oceans and can reach heights of a mile or two. And sometimes, so many spiders launch together that the ground becomes blanketed with spider silk. Spiders use ballooning to seek food, avoid danger, find a mate. But much is still unknown about the physics of spider flight. And that’s what drew Moonsung Cho to study them. Here he is in Berlin. You can see the path a ballooning spider takes after launching from his finger. Cho has carried out dozens of tests in nature. But for detailed analysis, he took spiders to the lab where he tested them in a wind tunnel. The researchers found that the spiders prefer mild breezes. And the silk they spin can measure up to six feet long. Amazingly, it seems to be not the breeze, but what you might think of as the stickiness of the air that holds them aloft. Imagine a thread suspended in a thick fluid, like a syrup. It won’t sink. And if the fluid is moving along, the thread moves with it. A strand of silk may be more than a thousand times thinner than a human hair. So for spider silk, the air is that fluid, moving swiftly along to take the spiders far afield. These spiders don’t need an actual balloon to fly, just their own amazing silk.