Army ants cross mighty rivers by climbing on top of each other and clustering together into a little ball that floats. Many of them fall off and sink, and naturally the ants on the bottom of the ball drown. The ones who are quick and vigorous enough to keep clawing their way to the top survive. A lot of them make it across, and that's why you can't stop army ants by dynamiting the bridges. That's how Refus come across the Pacific, even though they are too poor to book passage on a real ship or buy a seaworthy boat. A new wave washes up onto the West Coast every five years or so, when the ocean currents bring the Enterprise back.