Crabs & Crazy Ants on Christmas Island

     If I want to fall asleep quickly on school nights, I watch Blue Planet on Netflix. Before I started nodding off to sleep the other night, I heard the story of Christmas Island and the impact a tiny invasive species can have on an entire ecosystem. I did some more research because I was barely conscious when I heard it, so here goes:
     Christmas Island is a small island in the Indian Ocean that is home to large amounts of animal and plant species not found anywhere else in the world.

location of Christmas Island

     Warm temperatures, high rainfall, fauna, and isolation contribute to Christmas Island's plant life, but it is the red crabs that fuel the biodiversity of the forests. Red crabs are a keystone species on Christmas Island, they turn over the soil and fertilize it with their droppings, promoting plant growth. They also eat seedlings to control certain weeds from overtaking the forest.

A baby red crab being cute

adult red crabs grabbing plant snacks on their annual migration to the coast to breed

     Adult red crabs have no natural predators on the island. It is estimated that over 43.7 million adult red crabs lived on Christmas Island, however the accidental human introduction of the yellow crazy ant is believed to have killed 15-20 million red crabs in total. The movement of the red crabs across the forest floor causes the yellow crazy ant to spray formic acid in defense, blinding the crab so that it will eventually die from dehydration and exhaustion as it attempts to flush the acid out of its eyes. The decaying crabs are a source of protein for the ants and the abandoned crab burrows become ant nests. 

yellow crazy ants attacking an adult red crab

yellow crazy ants attack other species native to Christmas Island, this is a chick that was attacked and has lost its downy feathers, sight, and now has a deformed beak and reduced chances of survival

   Yellow crazy ants are a successful and dominant species on Christmas Island because of its aggression toward all other species, little aggression toward its own species, effective recruitment, and large colony size. Supercolonies of yellow crazy ants are the single greatest threat to Christmas Island's biodiversity, one was found to hold over 1,000 queens in a 6 meter plot of land!    

yellow crazy ant supercolony

     The yellow crazy ant has not only depleted the red crab population but the island's biodiversity and even the structure of its forests. The seedlings previously eaten by the crabs have spread and altered the forest structure, one of them being the stinging tree, which has hairs that cause severe pain when touched. Crazy yellow ants protect scale insects from their enemies in exchange for food in the form of honeydew. Scale insects feed on the forest canopy and because of their mutualistic relationship with the yellow crazy ants they have multiplied and killed mature trees. The interaction between these two invasive species has allowed their populations to grow to extremely high densities.

crazy yellow ants kissing and sharing honeydew from yellow lac scale insects

     Christmas Island is the focal point of an ongoing international effort. Christmas Island National Park staff, along with help from the Christmas Island Crazy Ant Scientific Advisory Panel and the Australian Government are working together to keep yellow crazy ant numbers in check. Lures and fences are being used to keep land crabs away from areas where supercolonies are being eradicated. A small wasp, Tachardiaephagus somervillei, was imported to Christmas Island in December 2016 to attack scale insects and destroy the yellow crazy ant's largest source of honeydew on Christmas Island. The good news is, controlling and reducing the scale insect population is expected to control and reduce the yellow crazy ant population. There is hope for Christmas Island after all!

temporary fences made to keep red crabs out of yellow crazy ant supercolonies

     Christmas Island's ecosystem was thrown into peril by humans. This is the case, time and time again. From lionfish destroying reefs, to burmese pythons overtaking Florida, to Japanese Knotweed in Rand Park. The actions of the Australian Government to fix human mistakes on Christmas Island is awe-inspiring, and it is one of the few times government has actually faced human caused environmental catastrophes. Funny how what should be the most important world issue is oftentimes thrown aside, ignored, even denied. Imagine if our government actually cared and did something about climate change and the destruction of ecosystems. We could stop the oceans from rising, save people's homes, and stop species extinction. Ecosystems can be healed, Christmas Island is proof. Our broken world can be fixed, our government just needs smart people who love and care about the fate of Earth, the beautiful blue planet that contains all known life in the universe.