The Project X team tracks the fallout when an outsider with bad manners and a voracious appetite disrupts the natural order of a paradise island ecosystem. Next they check out a clever way to head off invasive species before they get in, and finally they travel to Mexico, to find out what happens when an invader intrudes on the most private place you've got – your body
Dr. Brian Alters wings his way down to Gasparilla Island in south Florida to hunt for an exotic invader - the iguana. Initially brought to the island as pets, the iguanas loved their new spot in the sun so much that they took over within a decade. The population grew to 12,000 and now the locals are fighting back.
Marc Huot dives into the Great Lakes to look for another invasive species - the zebra mussel. It first hitched a ride on the hull of a ship from Russia in the 1980's and is now costing industry billions. But there is hope. Dr. Brian Fleck introduces us to "cavitation" - a new tool that engineers are using to rid a ship’s ballast water of exotic invaders once and for all.
Dr. Jennifer Gardy looks at bad - and good - invaders often found in our own bodies. Not only can tapeworms cause nasty tummy aches, but they've now been linked to epilepsy. And hookworms, common invaders in the developing world, can actually be good for you. They're being used to treat auto-immune diseases like asthma, hay fever and Crohn's disease.