is a unique natural habitat located in the Indian Ocean with many endemic species. The national park covers two-thirds of the island, which has been referred to as the Galapagos of the Indian Ocean.
Many people are aware of the red crabs whose mass migration to the sea has been described as one of the wonders of the natural world. Christmas Island has many other species of crabs, including the impressive robber crabs
). These may be the largest land-dwelling arthropod
Together these abundant land crabs clear the forests of leaf litter and maintain burrows that prevent soil becoming compacted, creating an open and diverse forest.
This thriving natural system, however, was disrupted by an invasive ant species known as the yellow crazy ant
) became abundant on the island.
The crazy ants spray formic acid
in the eyes and leg joints of the crabs, which immobilises them. The crabs soon die and become food for the ants. In some cases, crabs that live in areas free of crazy ants are killed during their annual migration and so never return to their original forest. This creates crab-free zones even where the ants do not live.
With fewer crabs, the forest has become less diverse, with a dense understory and compacted soils due to the collapse of crab burrows.