Humans have known for quite a while that some spiders engage in a kind of flying called “ballooning.” To balloon, spiders release a parachute-like web into the air (with themselves attached) and allow the wind to pick them up and deposit them in greener pastures. What humans did not know until very recently, however, is that these spiders actually check the weather before taking flight.
Biologists and mathematicians with Rothamsted Research in England first calculated the ideal flying conditions for spiders, finding cloudy fall and spring days to be the best. The group then compared those conditions against the actual numbers of balloon flights by spiders and found that peaks in ballooning actually correspond with the ideal conditions. Spiders, it seems, are waiting for the right weather before lifting off.