A Crabby Christmas

In the Indian Ocean, just west of Australia, there is a tiny island that is literally called Christmas Island. Admittedly, Christmas Island was simply named after the date it was discovered in 1643, and it is anything but a winter wonderland--indeed, it is covered in tropical rainforest (though, to be fair, there is plenty of mistletoe. . .). It serves as an important habitat for various species of birds, reptiles, and a few mammals. And crabs.
Every year, Christmas Island red crabs swarm to the shore of the island in their millions to release their eggs into the water. Interestingly, these swarms which are now threatened by human development on the island, may also be a result of human activity. In 1903, the MacLear's rat, one of the few mammals native to the island and a major predator of the crab, was killed off by introduced cats. With the rat gone, the crabs' population exploded. Yet today, a new invasive species is threatening the crabs--and much of the rest of the island as well.
This newcomer is the yellow crazy ant, an insect from Africa. These omnivorous ants will feed on anything they can overpower, and often kill and eat the small animals on Christmas Island. Crazy ants form what are known as "supercolonies": colonies with multiple queens that can coordinate with one another and effectively control a large area of forest. Because of this, they are notoriously hard to exterminate.
 However, progress has been made. In 2002, a poison-baiting program killed 99% of the crazy ant population in a test area, while leaving all of the red crabs alive.

Christmas Island red crabs like this one travel to the sea in gigantic swarms to lay their eggs. However, these migrations may be a thing of the past unless invasive ants are kept from devastating the island.