Though spiders are walkers, nimble afoot and wingless, they are not shy about taking to the sky. They spend much of their time suspended weightless and are always ready to take off. They may patrol gravity bound across acres of trackless foliage, but if their course leads them to a precipice so steep their tiny eyes cannot see the bottom, they step over the edge and off into space without breaking stride. As quick as a spider step, they affix a lifeline at their feet, jump as far as they can, and sail through the air with eight legs spread wide. Then they pull their tether tight to arrest their fall, turning their trajectory into a broad, swinging arc. [ . . . ]

When a spider feels the need to go for a sky ride, the habit of casting a streamer on the wind takes on another dimension. Spiders sit low on the food chain and rely on flight, rather than their bite, to save themselves. At the appearance of a threat (often in the form of a bigger arachnid), a small spider backed out onto the edge of a cliff pirouettes on the ledge to face the wind, raises his abdomen high, and in seconds broadcasts a bloom of silken lace onto the breeze. Then he leaps untethered into space and floats away, coming up suspended from the gossamer parachute he has just broadcast, hung by his silken line. He climbs to the center of the flimsy raft and continues to spin, fabricating a tenuous airfoil that will catch the wind and free him from the ground, carrying him he knows not where. [ . . . ]

Charles Darwin witnessed the invasion of his sailing ship HMS Beagle by a flight of spiders two hundred miles off the coast of South America. Such mass migrations demonstrate the potential of flying spiders. They are the first colonists to arrive on remote islands emerging from the ocean, or on barren fields of freshly cooled volcanic lava. Rising ever higher through the sunrise, settling to lower elevations by evening, the tiny fliers drift in loose formation a mile above the sea, their lacy, air-built balloons catching the amber light. They are watching from above, waiting for a hole in the wind through which they might drop in on promising new hunting grounds—sites from which, perhaps, they will not soon have to fly.

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