Robber crab (coconut crab)

How it lives

A robber crab is a land hermit crab. It breathes air with special lung-like tissue and can drown if kept under water for long. It is mostly active at night or in overcast weather and climbs well. Mating happens on land. The female releases larvae into the sea, where they drift for about 3 to 4 weeks, and the young then settle into snail shells until their abdomen hardens. Sexual maturity comes at about 5 years, the largest size after 40 to 60 years, and Parks Australia says they can live more than 50 years.

Where it goes

A GPS study on Christmas Island (2008 to 2011, 55 males) found two patterns. Some crabs stayed in place with short trips of about 25 m, while others made long trips of 0.7 to 4.2 km between the coast and the inland forest, mainly in the wet season, at up to about 150 m per hour. A crab's core area was about 0.2 ha.

We only draw a journey on the map when scientists have tracked it or clearly documented it. For this animal we have not found one yet.

Populations

Global: Vulnerable on the IUCN Red List. It was listed Data Deficient from 1996 and moved to Vulnerable in an assessment cited as 2020 (one source text says 2018). Hunting and habitat loss are the main threats. Christmas Island has the largest and densest population in the world according to Wikipedia, outnumbered there by more than 50 times by the red crab. Parks Australia calls it the world's largest and best protected population. Many crabs are killed by vehicles on the island every year, and road mortality monitoring began in January 2010 after traffic rose in late 2009.