[4] Christmas Island red crabs make an annual mass migration to the sea to lay their eggs in the ocean.

Although red crabs are diurnal, they usually avoid direct sunlight so as not to dry out, and, despite lower temperatures and higher humidity, they are almost completely inactive at night.

[3] At the end of the incubation period the females leave their burrows and release their eggs into the ocean, precisely at the turn of the high tide during the last quarter of the moon.

[5] For the first three years of their lives, the young crabs will remain hidden in rock outcrops, fallen tree branches and debris on the forest floor.

[5] Red crabs grow slowly, reaching sexual maturity at around 4–5 years, at which point they begin participating in the annual migration.

They mostly eat fallen leaves, fruits, flowers and seedlings, but will also feed on dead animals (including cannibalising other red crabs), and human rubbish.

[12] The yellow crazy ant, an invasive species accidentally introduced to Christmas Island and Australia from Africa, is believed to have killed 10–15 million red crabs (one-quarter to one-third of the total population) in recent years.

[4] In total (including killed), the ants are believed to have displaced 15–20 million red crabs on Christmas Island.

[15] Surveys have found a density of 0.09–0.57 adult red crabs per square metre, equalling an estimated total population of 43.7 million on Christmas Island.

[16] Based on genetic evidence, it appears that the Cocos (Keeling) red crabs are relatively recent immigrants from Christmas Island, and for conservation purposes the two can be managed as a single population.

As a result, thousands of red crabs are crushed by vehicles and sometimes cause accidents due to their tough exoskeletons which are capable of puncturing tires.