Many newly hatched spiders like to do something biologists have dubbed "ballooning," which basically involves building a kite out of their own webbing. A spider can catch updrafts on its "parachute" and sail anywhere from a few feet to a couple thousand miles, sometimes catching jet streams into the upper atmosphere for weeks at a time and always making sure to land directly on your face.
Well, we made that part up. They don't always manage to do that. Though spiders absolutely do routinely parasail across the country. The largest airborne spider ever recorded was still well under an inch in length, which seems like it should be comforting until you learn that thousands or even millions of spider "balloons" may get caught up in the same current and dumped over the same area like a scurrying, venomous blizzard.
Also, even tiny spiders look huge when they're dropping out of the sky and landing on your eyeball.