Christmas Island Red Crab

Merry Christmas everyone... On this festive day, I am bringing you to somewhere special. So hop in the boat and we are heading to Christmas Island!

Christmas Island is an Australian Non-self Governing External Territory, located in the Indian Ocean on the rim of South East Asia, 360km south of Java and 2600 km North West of Perth.


The Christmas Island red crab is by far the most obvious of the 14 species of land crabs found on Christmas Island. It is estimated that 120 million of these bright red land crabs live in their preferred shady sites all over the island.

What is so special about this red crabs?
It is The Annual Migration To The Ocean
At the beginning of the wet season (usually October / November), most adult Red Crabs suddenly begin a spectacular migration from the forest to the coast, to breed and release eggs into the sea.

Below is the video to show its impressive swamp of red invading the town. Basicly everywhere in the island.


Christmas Island Red Crabs - For more amazing video clips, click here

I find the rule in golf impressive! Perhaps that is the only place in the world where crabs can help you score in golf game. They are helpful in some ways. =)

Bright red is the common colour but there are the occasional orange specimens and more rarely some purple animals. They are a big crab. An adult body shell (or carapace) may measure up to 116mm across. The Christmas Island red crabs' carapace is round shouldered and encloses their lungs and gills.

Their claws are usually of equal size unless one is a regrowing claw. Males grow larger overall than females, while females have a much broader abdomen and usually have smaller claws than males.

Christmas Island red crabs grow slowly, reaching about 40mm in carapace width after 4-5 years. They are sexually mature at this age and begin to participate in the breeding migrations.

The Christmas Island red crabs moult their shells regularly during their early growth phases to match their increasing body size. Moulting usually takes place in the protected moist environment of their burrows. Mature Christmas Island red crabs probably moult only once a year, as their growth rate slows.

Red Crab Diet

Red Crabs diet consists mainly of fallen leaves, fruits, flowers and seedlings. They prefer fresh green leaves but will eat any fallen leaves. They are not solely vegetarian however. They will eat other dead crabs and birds, the introduced Giant African snail and palatable human rubbish if the opportunity presents itself.

Red Crab Habitat

Red Crabs are diurnal (active during the day) and almost inactive at night despite lower temperatures and higher humidity.
Crabs retreat into the humid interior of their burrows during the dry season. They plug the burrow entrance with a loose wad of leaves to maintain a high humidity level, and effectively disappear from view for up to two to three months of the year.

The Breeding Calendar

Males lead the first wave of the downward migration and are joined by females as they progress. Larger males arrive at the sea first (after about 5-7 days) but are soon outnumbered by females.

The crabs replenish moisture by dipping in the sea, then the males retreat to the lower terraces to dig burrows. The density of burrows is high (1-2 per square metre and fighting occurs between males for burrow possession. The females move to the terraces and mating occurs, usually in the privacy of the burrows that males have dug and fought for.

The females produce eggs within 3 days of mating and remain in the moist burrows on the terraces for 12-13 days while they develop. The eggs are held in a brood pouch between their extended abdomen and thorax. A single female can brood up to 100,000 eggs.

In the morning and late afternoon around the last quarter of the moon, the egg-laden females descend from the terraces to the shoreline. They pack into shaded areas above the waterline at densities of up to 100 per square metre in places. The females usually release their eggs into the sea toward dawn, around the turn of the high tide. Release of eggs may occur on 5-6 consecutive nights during the main breeding migration. After the first two days, eggless females may be seen crossing plateau roads, kilometres from the shore.

If the spawning migration is delayed or disrupted, usually because of unfavorable weather conditions, both male and female crabs will remain on the terraces for the next month and complete the spawning one lunar month later.

Larvae Grow To Baby Crabs In The Sea

The eggs released by the females hatch immediately on contact with the sea water and clouds of young larvae swirl near the shore before being washed out to sea by waves and tides. Millions of the larvae are eaten by fish and plankton feeders such as Manta Rays and the enormous Whale Sharks which visit Christmas Island waters during the crab spawning season.

After about a month in the ocean, and after growing through several larval stages, the surviving larvae have developed into prawn-like animals called megalopae. The megalopae gather in pools close to the shore for 1-2 days before changing into young crabs and leaving the water.

Impact Of Humans
Certain human activities have led to increased numbers of Red Crabs dying during their annual migration to the sea.
To reduce the number of crabs killed by vehicles during the migration, 'crab crossings' are being constructed in roads which cross main crab migration paths. Points where high numbers of Red Crabs cross roads have been identified, and tunnels are built under the road for crabs to pass through. Walls that the crabs can not climb over are built alongside the road to 'funnel' the migrating crabs through the tunnels. These crab crossings may be seen on the Lily Beach road. Other conservation measures used by the community are road closures and traffic detours around the major migration paths during peak periods of the migration.

The Annual Migration To The Ocean

At the beginning of the wet season (usually October / November),
most adult Red Crabs suddenly begin a spectacular migration from
the forest to the coast, to breed and release eggs into the sea.
The timing of the migration breeding sequence is also linked to the phases of the moon, so that eggs may be released by the female Red Crabs into the sea precisely at the turn of the high tide during the last quarter of the moon. It is thought that this occurs at this time because there is the least difference between high and low tides.

Movement peaks in the early morning and late afternoons when it is cooler and there is more shade. If caught in open areas, in unshaded heat, the crabs soon lose body water and die.

Have a Merry Christmas and Happy New Year 2010! ! 2009 has been a remarkable year for me, some of the unhappiest thing and happiest things happen to in 2009. Certainly a year to remember in my diary. Be safe and take care.

Love the Ocean. Protect the Ocean.

Please leave your comments in the chatbox at the bottom of page. Thank you.

For more info, visit :

http://www.christmas.net.au/exp_red_crab_migration.html