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The most well-known and the most numerous of these animals, and the one whose image makes it onto souvenir dish towels and onto soft toys, golf balls, whiskey tumblers, shot glasses, postcards, T-shirts, rubber figures, and ceramic ornaments, is the famous Christmas Island red crab. Its numbers far exceed the human population; at the last official count, the red crab population exceeded 120 million.3 The red crab, or Gecarcoidea natalis (Pocock, 1888), is a large crab, measuring about 116 mm across the broadest part of the carapace. They grow slowly and get to be about 40 mm in width after about 5 years of life. They moult frequently in early life then less rapidly as they age (Green, 2004). These crabs live solitary lives except when they are migrating during their breeding season, which they do en masse in an annual spectacle of ancestrally driven scarlet movement. Otherwise, they live solitary diurnal lives in single chambered burrows, in which they do not tolerate intruders. They eat fallen leaves and fruit and have a decided preference for young, fresh growth on young plants within their reach. The crabs are efficient at removing seedlings and weeds from the forest floor and are therefore important in maintaining the structure of the island forest (see Green et al., 1999). If the opportunity presents itself, they will eat dead animals, including their own kind, and any human rubbish that is edible.
There are considerably less red crabs than there used to be, though, owing to an invasion of yellow ants. The ants, which came ashore by ship between 1915 and 1934 and thrived in the island conditions, predate the crabs by spraying toxic liquid under the crabs’ carapaces, leaving them to die and then eating them from the inside out.4
Unique to the island, the still numerous scarlet crustaceans are roused from their regular scuttling and grazing activity, in the lush and damp places of the island, by seasonal ancestral callings to the ocean, where they take on salts and fling their eggs out to the sea to develop and hatch. The crabs follow their ancestral routes to the sea every year, ringing the island in a scarlet halo that can be seen for hundreds of meters out to sea and, even more spectacularly, from the air. During these migrations, the island appears as a moving red carpet, even though the crabs are funnelled under road routes by purpose-built tunnels. The whole place, as one man told me, ‘moves under your feet’.