Christmas Island reptile killer mystery solved

Threats to Christmas Island Wildlife

Christmas Island is located in the Indian Ocean and is about 360 km south of Java. Despite its small size (it measures approximately 19 km by 14.5 km), its fauna is incredibly diverse, with many species found only on the island and nowhere else. About two-thirds of the island has been declared a national park and includes rainforests, coral reefs, wetlands and seashores.

Perhaps its most famous animal resident is the Christmas Island crab. Every year, millions of these land crabs will make a spectacular annual mass migration to the sea to lay their eggs. It is an important species on the island, as they feed on fallen fruits and leaves, as well as seedlings and carrion. They also dig burrows and fertilize the ground with their droppings, which improves the soil. However, these are not the only crabs on the island – there are around 50 native species.

The island was only settled by humans in the late 1800s and there are no large native land mammals. The introduction of rats, cats and dogs led to the decline or extinction of native mammals.

Other introduced species, such as the common wolf snake and the giant centipede, have also been implicated in the decline of the island’s native fauna.

Perhaps the most destructive invasive animal is not a large mammal, but the brilliantly named “yellow crazy ant”. The iconic Christmas Island crab saw its numbers plummet following the accidental introduction of the ant in the first half of the 20th century.

In the absence of predators on the island, the yellow crazy ant can form huge supercolonies, with densities of up to 2,254 foraging ants per square meter. The ants killed millions of crabs, which affected the diversity of plants found in the rainforest: with fewer crabs eating the seedlings, the weeds thrived.

But it’s not just red crabs that have been affected by the invasive ant. Yellow crazy ants will also fight their way through native frogs and lizards, as well as baby birds.

Currently there are programs in place to try to control the ants on the island.

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