In 1918, a shipwreck at the Lord Howe Island, Australia, introduced black rats which proceeded to eat the native species of walking sticks so large that they were called "tree lobsters." In two year's time, the Lord Howe stick insect, Dryococelus australis, went extinct.
Or so, scientists thought. Turns out, a small population of 24 somehow managed to escape to a spindle of rock in the middle of the ocean. They live off one spindly little bush there for 80 years, hidden away from the world, until rock climbers spotted them some years ago.
What comes next is the heroic effort of scientists to save the large insects from going extinct (again). Robert Krulwich of NPR has the fascinating story:
Fast forward to 2001, when two Australian scientists, David Priddel and Nicholas Carlile, with two assistants, decided to take a closer look. From the water, they'd seen a few patches of vegetation that just might support walking sticks. So, they boated over ("Swimming would have been much easier," Carlile said, "but there are too many sharks."), they crawled up the vertical rock face to about 500 feet, where they found a few crickets, nothing special. But on their way down, on a precarious, unstable rock surface, they saw a single melaleuca bush peeping out of a crack and, underneath, what looked like fresh droppings of some large insect.
Where, they wondered, did that poop come from?
The only thing to do was to go back up after dark, with flashlights and cameras, to see if the pooper would be out taking a nighttime walk. Nick Carlile and a local ranger, Dean Hiscox, agreed to make the climb. And with flashlights, they scaled the wall till they reached the plant, and there, spread out on the bushy surface, were two enormous, shiny, black-looking bodies. And below those two, slithering into the muck, were more, and more ... 24 in all. All gathered near this one plant.
They were alive and, to Nick Carlile's eye, enormous. Looking at them, he said, "It felt like stepping back into the Jurassic age, when insects ruled the world."