It turns out that one of nature's most foolproof navigators is none other than the Caribbean spiny lobster. Various attempts to disorient lobsters--which involve goofy things such as taking them away from their homes while they're wearing eye coverings--never succeed. But when spiny lobsters are placed in special boxes that generate a magnetic field similar to one found north of the lobsters' home, the lobster tries to go south. When the magnetic field generated is the same as one south of the lobsters' home, it tries to go north.
Busted--these little spineless Cortezes do what birds do when they migrate to warmer pastures every year. They orient themselves by sensing the magnetic field of the earth. That's a good trick for an invertebrate already, but think for a second about what I just said. A flock of birds or a herd of giraffes may be able to migrate across miles and miles using a magnetic sense. These lobsters, however, can find their way straight home from a few hundred yards away. Is that easier or harder?
Using magnetic sense, it's actually much harder. Because the earth's magnetic field varies so little from point to point, it's a simpler thing to sense its changes over a hundred or a thousand miles. Using it to do fine-tuning navigation is like searching for a matchbox with a map of the U.S. But the spiny lobster does it. Apparently, not only do they have a magnetic sense, they can do what's called "magnetic position fixing"--recognizing differences in the earth's magnetic field of down to one one hundredth of one percent. Now that's a navigator.