In recent years, the Australian island of Christmas Island has become synonymous with one thing: red crabs. Each year, millions of these bright red creatures emerge from the island’s forests and make their way to the ocean in a mass migration that has become a major tourist attraction.

While the sight of so many crabs can be a little unnerving at first, it’s hard not to be impressed by the sheer scale of the event. And despite their somewhat ominous appearance, these crabs are actually an important part of the island’s ecosystem.

So just what are these creepy crawly creatures, and why do they take over the island each year?

Red crabs are a species of land crab that are found only on Christmas Island, which lies in the Indian Ocean roughly 2600 km northwest of Perth. They are easily recognizable thanks to their bright red carapace, or shell, which helps to protect them from predators. Adult crabs can grow to be up to 11 cm wide, making them one of the largest land crab species in the world.

Each year, the red crabs undergo a mass migration from their forest habitats to the coast, where they mate and release their eggs into the ocean. This event, which usually takes place in November or December, is triggered by the arrival of the wet season, which makes it easier for the crabs to make the journey.

During the migration, the island’s roads are closed to vehicles, and people are encouraged to stay indoors and avoid disturbing the crabs. This is important not just to protect the crabs themselves, but also because they play a vital role in the island’s ecosystem. Red crabs are responsible for aerating and fertilizing the soil, and they help to control the spread of invasive plant species.

Despite their importance, red crabs are under threat from a number of factors, including habitat loss, climate change, and the introduction of non-native species to the island. Efforts are underway to protect the crabs and their habitat, including the construction of crab crossings to help them navigate busy roads.

So if you’re ever lucky enough to find yourself on Christmas Island during the migration season, don’t be put off by the creepy crawlies. Instead, take the opportunity to witness one of the natural world’s most impressive spectacles, and to appreciate the important role that these bright red creatures play in their island home.

Video: