The Red Crab Migration – World's Most Dramatic Animal Migration

Christmas Island’s Red Crab Migration

Facebook just reminded me of my friend Kathy with a picture I posted on it 10 years back and took me back to those good old Newcastle days. So, I decided to make a call to her.

“Me: Hey Kathy! How are you?

Kathy: I'm doing great sweetie! Hope you are well.

Me: What’s up?

Kathy: I was just thinking about how lucky I am to be on Christmas Island right now. I’m really thrilled to tell you that today I’m going to go for a walk and click with the red crabs.”

Wait, Did I hear it right? A picture with red crabs?

What is so special about them?

So, I decided to google about it a bit and saw that everyone is talking about Christmas Island’s Red Crab Migration – World’s most dramatic animal migration.

The enormous red crab migration on Christmas Island is one of the most spectacular natural phenomena on the planet. Every year millions of these massive crabs leave their burrows on Christmas Island, north-west of Australia, and swarm across the roads, streams, rocks and beaches on their journey to the ocean to mate and spawn. This colourful migration begins when the wet season’s first rains fall, which normally happens in October or November but has been known to occur in December or January.

As I explored further to learn more, I found that red crabs can attain a carapace width of 120 mm and a mass of 500 grams. Male crabs are typically larger than female crabs, with adult females having a significantly wider belly and smaller claws. As the name suggests, their most common hue is bright red, although they can be orange or the extremely uncommon purple. They are active at different times of the day and moisture appears to be the most important indicator of surface activity. During dry periods, the crabs retire to the interior of their burrows, but when it rains, they emerge quickly. According to surveys, there are 0.09–0.57 adult red crabs per square metre on Christmas Island, equating to a total population of 43.7 million. They are the dominant consumers on the forest floor and due to this, they have little or no competition for food. These animals have the potential to be the most important influencer of the pattern and process of the Christmas Island rainforest due to their abundance and vast distribution.

The environment of the Christmas Island rainforest relies heavily on red crabs. They are opportunistic omnivorous scavengers that feed on leaves, fruits, flowers and saplings, although they also devour dead animals and human garbage. They recycle the nutrients found in their food and their cylindrical brown droppings act as a fertilizer on the forest floor. Their burrowing rotates and aerates the soil, and the selective browsing of their seeds and seedlings contributes to the distinctive structure and composition of the Christmas Island rainforest.

Aren’t they amazing creatures? Now, let’s take a peek into the most-talked-about red crab migration and the role that the island’s community plays in it.

The red crab migration is the world’s most dramatic animal migration. The peak migration period lasts 18 days. The females follow as the huge male crabs lead the migration from the rainforest to the Indian ocean. They march through towns together, crossing specially constructed bridges and obliterating whatever is in their way. However, the crimson creatures sidle along the shore for a few days before vanishing to establish mating burrows on terraces. Once the mating has occurred in or near the burrows, the male crabs retrace their trip back home, but the females stay behind until they are ready to lay eggs. Females stay in the burrows for two weeks while the eggs mature and rush the beach to discharge their eggs into the water during the spawning phase. And then, baby crabs are born if the larvae hatching from the placed eggs are not devoured by fish or sharks and spend 3–4 weeks there before they return to the island as juvenile crabs. Often, the larvae are totally destroyed by predators that visit them during the season, but once or twice a decade, a bigger number of larvae stay, sustaining population levels on the island. The juvenile crabs will spend their first three years of life hiding among rock outcrops, fallen tree branches and detritus on the forest floor. They mature slowly, reaching sexual maturity at the age of 4–5 years when they begin to migrate annually.

The voyage of the Christmas Island crab is perilous since it risks dehydration in the blazing tropical heat and must navigate busy highways to reach the sea. On the way, another peril awaits. Yellow crazy ants for super colonies that attack their victims by dousing them in acid and aiming at their eyes and mouth. Crabs that have been blinded are rendered powerless and eventually perish. And, those that survive scramble down the beach, risk more attacks by the sea gulls or Moray eels before rehydrating in the water.

Each step should be taken with caution as crabs clog the roadways, broad walks and beaches. Crabs on Christmas Island, luckily, have right of way. Parks Australia has constructed barriers and fences along highways to divert crab crossers to safety, reducing the number of crabs killed by vehicles during the migration. To allow crabs to get through, “crab crossing grids” have been installed into highways that straddle major crab migratory lines. Road closures and traffic delays along main migratory corridors are also employed by the community during peak migration seasons as conservation measures.

The red crab’s migration is the island’s most popular tourist attraction. The crab’s laborious journey is a key annual event for the island, with visitors and nature enthusiasts flocking to coves and beaches to watch it. Visitors are permitted to wander among the crawling crabs, albeit care is urged. Drumsite, Flying Fish Cove, Ethel Beach and Greta Beach are the best spots to witness migration and spawning.

Now I see why Kathy is so excited. Let’s tune in for some amazing footage of the most-wanted animal migrations. I can’t wait to hear the pitter-patter of red crabs wandering the lanes of Christmas Island.

References:

“A Red Hot Idea to Save Christmas Island’s Famous Red Crabs – Australian Interstate Quarantine.” n.d. Accessed November 24, 2021. https://www.interstatequarantine.org.au/a-red-hot-idea-to-save-christmas-islands-famous-red-crabs/.

“Christmas Island Crab Migration.” n.d. Accessed November 24, 2021. https://www.slideshare.net/jcarpente/christmas-island-crab-migration.

“Christmas Island Crabs Flock to the Sea Once Again in Annual Mass Migration - The Washington Post.” n.d. Accessed November 24, 2021. https://www.washingtonpost.com/world/2021/11/18/christmas-island-red-crabs-australia/.

“Christmas Island Red Crab - Wikipedia.” n.d. Accessed November 24, 2021. https://en.wikipedia.org/wiki/Christmas_Island_red_crab.

Green, Peter T. 1997. “Red Crabs in Rain Forest on Christmas Island, Indian Ocean: Activity Patterns, Density and Biomass.” Journal of Tropical Ecology 13 (1): 17–38. https://doi.org/10.1017/S0266467400010221.

“March of the Red Crabs | BBC Earth.” n.d. Accessed November 24, 2021. https://www.bbcearth.com/news/march-of-the-red-crabs.

“Red Crab Migration | Christmas Island National Park.” n.d. Accessed November 24, 2021. https://parksaustralia.gov.au/christmas/discover/highlights/red-crab-migration/.

“Sea of Red as Millions of Crabs Bring Christmas Island to a Standstill during Annual Migration - Caters News Agency.” n.d. Accessed November 24, 2021. https://www.catersnews.com/stories/animals/sea-of-red-as-millions-of-crabs-bring-christmas-island-to-a-standstill-during-annual-migration/.

“The Strange Ritual Migration of 50 Million Red Crabs on Christmas Island - LifeGate.” n.d. Accessed November 24, 2021. https://www.lifegate.com/migration-red-crabs-christmas-island