Overview: Feeling a little cramped? Well just meet our line-up of animals that swarm in the millions, and you'll soon realize space really isn't an issue for these mobsters. The Most Extreme: Swarms hunts out the biggest hordes in the animal kingdom and compares them to the largest of human gatherings. We're not talking about get-togethers of several hundred; we're talking millions, and even billions! From Texan caves containing up to 20 million bats and a 300ft pile of bat guano, to the Christmas Island where each year there's a stampede of 120 million red crabs, and on to the Mexican mountain ranges where more than 220 million monarch butterflies can arrive after a 3000 mile migration to their wintering grounds, we travel across the globe seeking out the ultimate swarms. And did you know that to carry out his job on Christmas Eve, Santa and his reindeer would have to visit 667 million children in 1,300 houses per second and travel a total of 111 million miles at a speed of 3.6 million miles pe