Red crab invasion

Ranger Rick, Jan, 1998 by Leslee Elliott

A creeping carpet of bright red crabs adds a holiday touch to a tiny tropical island.

Christmas Island is decorated in holiday colors each year, starting in November. The green is always there--from the leafy rainforest. But the red is from 120 million red crabs suddenly on the go!

For days, this lonely island way out in the ocean (see map on page 9) will be crawling with crabs. The ones that go through town flood over roads and railroad tracks, run up stairs and through houses, crawl under beds and into closets, and climb up walls, across ceilings, and into sinks. The schoolboys in the photo at left show off crabs they've captured in the classroom!

If you visit Christmas Island at just the right time, you might see 80,000 red crabs for every human that lives there.

FOREST LIFE

The townspeople of Christmas Island never see a red crab during most of the year. From January through October, the crabs are on rainforest food patrol. They eat mostly leaves, but also fruits, flowers, and sometimes small creatures. With so many crabs munching away, they quickly "recycle" the stuff that drops to the forest floor.

Even though they live on land, red crabs must keep their bodies moist to survive. So, on the driest days from August to October, they seal themselves in burrows in the damp rainforest soil. They come above ground only on the most humid days.

DOWN TO THE SEA

As November approaches, the humidity in the air creeps higher and higher. The wet season is almost here. When the first heavy rain falls, the crabs really come to life. Finally they're off! Crawling out of the forest by the millions, they head toward the coast.

First come the males and then the females, swarming over everything in their path. Between the forest and the ocean on one part of the island is a town full of people. Their lives do not go on as usual.

There's no escape from this yearly event. A strange noise fills the air. One crab moves with barely a sound. But 600 million pairs of legs scuttling through the grass sounds like steady rain.

Kids still go to school every day--but in the company of crabs! Bikers and car drivers try to steer around crabs in the street. The crabs' claws are so sharp that running over a crab can mean a flat tire. But most people aren't annoyed. In fact, many take time to wet down crabs that are in danger of drying out or to help them out of tight spots. They want the crabs to make it safely to the coast.

GETTING DOWN TO BUSINESS

The fastest crabs finally reach the shore and take a quick dip. The males move back onto land to dig nesting burrows, often fighting over the "best" spots. The females arrive later, and mating takes place in the burrows. Then the males head back to the forest. Their mates stay in the burrows for a couple of weeks while their eggs develop.

On a high-tide night, the females leave the burrows and head for the ocean all at once. Each carries a heavy load of eggs in a pouch on her underside. When she reaches the beach, she raises her big claws and waves them toward the sky. Then she starts a shimmy-shaky, swaying hula dance. This releases her eggs into the sea. When the job is done, she begins the long crawl home to the forest.

IT'S A BABY BOOM

The eggs hatch into tiny larvae. There are so many larvae floating around that they darken the sea. Nearly a month later, in January, the larvae have turned into tiny crabs, each about the size of one of your fingernails. That's when they leave the water for the run of their lives.

A red carpet of miniature crabs crawls up the cliffs and rushes toward the forest. The babies hurry to get to this cool, damp place before they dry up in the daytime heat. They also must keep from getting crushed by cars and footsteps, or getting snatched by hungry birds and larger crabs.

FRESH START

The babies are so tiny, they often blunder into trouble when they stampede through town. People do everything they can to keep the little guys out of harm's way. They soak the hot ground with hoses. They scoop out buckets of babies trapped in drains. They stop to help them scramble across roads and train tracks.

Before long, the surviving babies make it to the safety of the forest. They seem to disappear and won't be seen again for several years.

Then another rainy season comes to Christmas Island. Millions of crabs leave the forest and migrate to the shore to make new babies. Life marches on!

READY OR NOT, HERE WE COME! These crabs are leaving the forest to start their mating march. Later, each male will dig a burrow and wait for a mate. The two males at right duel over a burrow. The bigger one seems to say, "Shove off, shrimp--I was here first!"

THEY'RE EVERYWHERE! Crabs turn up in some of the strangest places--such as gym class (above). The kids just keep right on playing ball! As the sign below warns, crab-covered roadways can be trouble for people and crabs. Several tunnels in town help the crabs cross in safety (left).

AHHH--QUICK DIP. Finally the crabs reach the beach (below). The first order of business is a refreshing dunk in the water.