Christmas Island Red Crabs

Christmas Island Red Crab

The Incredible Christmas Island Red Crab Migration

Christmas Island, a small Australian territory in the Indian Ocean, is home to one of the most spectacular natural wonders on Earth: the annual migration of millions of red crabs. Every year, these fascinating creatures emerge from the island’s forests and make their way to the coast to breed, creating a breathtaking display of color and movement.

  • The most spectacular aspect of the Christmas Island Red Crab’s behavior is their annual breeding migration. Each year, usually synchronized with the onset of the rainy season, millions of these crabs journey from the forest to the coast to spawn. This migration is so massive and synchronized that it can disrupt normal life on the island, including traffic.
  • A single female Christmas Island Red Crab can carry up to 100,000 eggs, which she incubates for about two weeks before releasing them into the ocean.
  • While primarily herbivores, feasting on fallen leaves, fruits, flowers, and seedlings, these crabs are not strict vegetarians. They will scavenge and eat other dead crabs, birds, and even the introduced giant African snail, showcasing their opportunistic dietary habits.
  • Due to their large numbers on Christmas Island, Red Crabs dominate the forest floor. This allows them minimal competition for the abundant food resources available, influencing the ecosystem significantly.
  • By consuming large quantities of vegetation, they influence the types of flora that grow in their habitats. Their scavenging helps to clean up dead organic material, and their digging activity helps aerate the soil.

What is the Christmas Island Red Crab?

The Christmas Island red crab (Gecarcoidea natalis) is a species of land crab that is endemic to Christmas Island and the nearby Cocos (Keeling) Islands. They are large crabs, with males reaching up to 116 millimeters (4.6 inches) in carapace width. While most are a bright red color, some can be orange or even purple.

Red crabs play a vital role in the island’s ecosystem by helping to decompose leaf litter, dispersing seeds, and providing food for other animals. It’s estimated that there are around 40-50 million red crabs on Christmas Island alone.

Christmas Island Red Crab Migration
Christmas Island Red Crab Migration

The Annual Red Crab Migration

The annual red crab migration is one of the most incredible natural spectacles on the planet. At the beginning of the wet season (usually November or December), millions of red crabs simultaneously leave their burrows in the forest and start marching towards the coast to breed.

The exact timing and speed of the migration are determined by the lunar cycle. The crabs always spawn before dawn on a receding high-tide during the last quarter of the moon. If the rains are late, the crabs may have to rush to make it in time.

Mating and Spawning

Once the male crabs reach the coast, they dip in the ocean to replenish moisture before burrowing into the sand to await the females. When the females arrive, mating occurs in or near the burrows.

After mating, the males return to the forest while the females remain in their burrows for about two weeks as their eggs develop. Each female can produce up to 100,000 eggs, which she holds in a brood pouch under her abdomen. This high fertility rate is necessary to ensure the survival of the species, given the many hazards the larvae face in their early life stages.

On the precise night of the last lunar quarter, the egg-laden females emerge from their burrows and release their eggs into the sea before returning to the forest. The larvae hatch immediately upon contact with water and begin their own incredible journey of development and survival.

Christmas Island red crab moonlight spawning
Christmas Island red crab moonlight spawning

Witnessing the Migration

Visitors to Christmas Island can witness the red crab migration at several locations, including Flying Fish Cove, Drumsite, Ethel Beach and Greta Beach. Raised boardwalks and bridges help protect the crabs from being crushed by vehicles, and park staff are on hand to assist visitors. Watching the sea of red crabs blanketing the island is an unforgettable experience.

Despite their numbers and dominance, the Christmas Island Red Crabs are vulnerable to disruptions by invasive species. For example, the accidental introduction of the yellow crazy ant has had devastating effects on the crab population, as these ants attack and can kill the crabs in large numbers.

Frequently Asked Questions

Q: Can you eat Christmas Island red crabs?
A: No, Christmas Island red crabs are not considered edible due to their small size and poor meat quality. They are protected by law and play a vital ecological role on the island.

Q: Why are there so many crabs on Christmas Island?
A: Scientists believe the large red crab population may be a result of the extinction of the endemic Maclear’s rat in 1903, which was likely a key predator of the crabs. With few natural predators, the crab population has grown to its current impressive size.

Q: How big do Christmas Island red crabs grow?
A: Male red crabs can grow up to 116 mm (4.6 inches) across the carapace, while females are slightly smaller. The males also have larger claws.

Q: How long do Christmas Island red crabs live?
A: Christmas Island red crabs are estimated to live up to 12 years. They reach sexual maturity at 4-5 years of age when they begin participating in the annual breeding migration.

The Christmas Island red crab migration is one of the most awe-inspiring events in the natural world. Witnessing millions of these colorful creatures marching in unison across the island is an experience that will stay with you forever. By understanding and appreciating the vital role these crabs play in the island’s ecology, we can help ensure that this incredible phenomenon continues for generations to come.