Spiders don’t just use their silk threads to build webs. They also spin sails to catch the breeze, sometimes flying hundreds of kilometers. This behavior — called ballooning — has helped spiders disperse all over the globe. To find out more about how spiders launch, scientists in Germany collected some large, orb-web-spinning crab spiders in a park outside Berlin. They put the spiders on a mushroom-shaped platform outdoors, and observed how the spiders behaved under different wind conditions. They also put the arachnids in a wind tunnel, where the scientists could carefully control wind speed and temperature. The spiders didn’t release their silk balloons at random. Instead, they tested the wind by raising their front legs in the air for about 6 seconds. When it was cold and windy, the spiders hid. But when the breeze was warm and gentle — less than 3 meters per second — the spiders spun out a triangular sail made of silk threads. Spiraling updrafts lifted the sails, and the spiders were on their way. It’s clear these crab spiders wait for the right conditions before takeoff. The next question is, can they control where they land?