Every year in late spring, Australia’s Christmas Island
becomes covered in crabs when the more than 40 million red crustaceans
that call the northwest island territory home start their annual
migration to the sea, covering the landscape in a mass of crimson claws.
The migration starts with the first heavy rains in October, November
or December. At that point, there’s enough moisture in the air for the
large crustaceans, which can reach up to 11cm across, to make the
arduous, five-day journey from their homes in wet inland forests to the
Indian Ocean, covering up to 9km along the way.
so many of the creatures on the move, Parks Australia works before and
during the migration to protect the crustaceans by closing roads,
building fences and constructing underground tunnels. Drivers are
encouraged to stop for the crabs.
Upon reaching the sand, the male crabs dig burrows and fight each other
for ownership of the shelters. When the female crabs arrive (usually
five to seven days after the first males), they begin to mate, and the
females stay in their beachside burrows until the last quarter of the
lunar cycle. The females always wait for the first day of the last
quarter – regardless of when they started the migration – to spawn and
release their eggs into the sea. Researchers speculate that since this
phase of the moon has the least sea level change between high and low
tides, the eggs have higher chances of survival.
This year, the possible spawning dates (and dates of the quarter moon)
are 28 November or 28 December, so the initial migration will happen
seven to 18 days before, depending on the weather. The crabs tend to be
on the move in the morning and early evening when the air is cooler, but
any dry spells will halt the migration until wetter weather prevails.