Guide · Indian Ocean ·
Christmas Island red crab migration: when to visit
Christmas Island red crab migration starts at the beginning of the wet season, usually in October or November. That is when most adult red crabs leave the forest and walk to the coast to breed. The park says the rains bring the damp, cloudy weather the crabs need for the long trip. The moon then sets the date the eggs are released.
This guide explains what you will see, how the timing works, where to watch, and what visitors can do to keep the crabs safe. It is general travel information, so check with the park for the latest news before you book.
Sources for this section: Christmas Island National Park, Red crabs (breeding and migration).
What the migration is
Red crabs live in the island's rainforest for most of the year. Each wet season, most of the adults move downhill to the sea. The park says breeding is usually in step across the whole island, so large numbers of crabs are on the move at the same time.
Some smaller groups of crabs travel earlier or later than the main wave. The park says these smaller migrations follow the same moon pattern as the big one.
The crabs have to cross roads and cleared ground on the way. Many thousands of adults and young crabs are crushed by vehicles, and crabs can dry out on open ground. Some crabs face three or four such hazards on the trip to the sea and back. That is why the park runs a set of protection measures, covered below.
Sources for this section: Christmas Island National Park, Red crabs (breeding and migration).
How rain and moon set the timing
Two things control the migration: the first heavy rains and the phase of the moon. The park explains it this way.
- Rain starts the walk. The wet season usually begins in October or November. The rain keeps the air damp, which helps the crabs travel without drying out.
- The moon sets the egg release. Females release their eggs into the sea at the turn of the high tide during the last quarter of the moon. At that time the sea level changes the least for a longer period, so it is safer for the females at the water's edge.
- Release often runs for several nights. The park says eggs may be released on five or six nights in a row during the main migration.
What this means for a trip: the migration is not on a fixed calendar date. It follows the weather, so the start can shift from year to year. Plan for a window of weeks, not one day.
Sources for this section: Christmas Island National Park, Red crabs (breeding and migration).
The breeding sequence
The trip to the coast follows a clear order. Males lead the way down, and the females join them as they go. The biggest males reach the sea first, after about five to seven days, but the females soon outnumber them. The main trip can last up to 18 days. The crabs move most in the early morning and late afternoon, when it is cooler and shadier.
At the shore the crabs dip in the sea to take on moisture. The males dig burrows on the lower terraces, and they fight each other for the best ones. The females follow and mating takes place. The males then head back inland.
The females lay their eggs within three days of mating. They stay in damp burrows for 12 to 13 days while the eggs develop in a brood pouch. A single female can carry up to 100,000 eggs. Near the last quarter of the moon, the females go down to the shore. They gather in shaded spots above the waterline, in some places at up to 100 crabs per square metre. They usually release the eggs toward dawn.
The eggs hatch the moment they touch sea water. After about a month at sea, the surviving young return as tiny crabs about five millimetres across. They take about nine days to walk inland to the plateau.
Sources for this section: Christmas Island National Park, Red crabs (breeding and migration).
Where to watch
The park lists four easy places to see the migration and the females spawning: Drumsite, Flying Fish Cove, Ethel Beach and Greta Beach.
- Check notice boards and radio. Updates on crab movements are given on public notice boards and local radio.
- Expect short road closures. At peak times, road sections where many crabs cross may be closed to vehicles for short periods.
- Park and walk. The park says you can park your vehicle and carefully walk among the crabs as they move to and from the shore.
- Look early or late. Egg-laden females go down to the shoreline in the morning and late afternoon around the last quarter of the moon.
- Expect roads to be closed. The park says some road and track sections are closed to vehicles for periods during the migration.
Sources for this section: Christmas Island National Park, Viewing the crab migration; Visitor activities.
How visitors help protect the crabs
Crabs and cars do not mix. The park says road crossings are one of the biggest dangers on the trip, so it has built several protections.
- Crab crossing grids are built into roads that cross the main crab paths. Crabs pass through them and under the road.
- Walls or plastic fencing that crabs cannot climb stand beside the roads. They keep crabs off the road and guide them to the grids.
- Roads are closed and traffic is sent on detours around the major migration paths at peak times.
As a visitor, follow any detour signs and drive slowly. Steer around crabs and watch where you walk, so you do not step on one. The park says crossings can be seen on most major roads.
Sources for this section: Christmas Island National Park, Red crabs (breeding and migration).
Planning your trip
Christmas Island is in the Indian Ocean, and the national park is run by the Australian Government. The park lists walks, fishing, boating and diving, and guided tours, as well as crab viewing. Camping is allowed at Dolly Beach and at the Pink House Research Station, with a permit. Ask the park office about permits, facilities and getting there before you book. Its postal address is PO Box 867, Christmas Island, Indian Ocean 6798.
Roads can be slippery when it rains, and some are suited only to four wheel drive vehicles. Cars of both kinds can be hired from several companies on the island.
Because the start date depends on rain, book flexible flights and rooms if you can. Plan to stay several days so you have a chance to see the crabs reach the shore. For other warm-weather trips, see the Great Barrier Reef day trips guide or browse all our guides.
Sources for this section: Christmas Island National Park, Visitor activities and home page.
Sources
- Christmas Island National Park, Red crabs: environment.gov.au
- Christmas Island National Park, Viewing the crab migration: environment.gov.au
- Christmas Island National Park, Visitor activities: environment.gov.au
- Christmas Island National Park, home page: environment.gov.au