Red Crab Eggs

Red crab eggs hatch in the ocean into larvae which change into little crabs when they reach land. The crabs migrate based solely on instinct, and survive hazards because of their large numbers.

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Red crabs are native to Christmas Island, Australia. The central plateau of Christmas Island is dominated by strands of rain forest. The island has a tropical climate and experiences both a wet season (December through April) and a dry season (May through November).

More than 120 million red crabs can be found on the rain forest floor of Christmas Island. Red crabs live alone in dirt burrows, or deep rock crevices. Crabs stay in the shade of their dwelling for most of the year. In October or November, when the wet season is about to return, crabs begin their migration to the shore. This timing coincides with the lunar cycle and the tides.

This video documents the third and final stage of the red crab migration, after the eggs have been released into the ocean. The crab larvae remain in the water for about a month, growing through several larval stages. Few are able to survive the harsh ocean currents and marine predators. Those that survive shed their larval casing and begin the journey back into the rain forest, battling predators, such as the yellow crazy ant, along the way.
1. How long do the red crab eggs drift in the ocean?
  
  Show Answer
  
  Red crab eggs drift in the Indian Ocean for about three weeks. During this time, the eggs hatch and morph into larvae.
2. What guides young red crabs on their migration route?
  
  Show Answer
  
  Young red crabs are driven by instinct to trace the path of their ancestors.
3. What hazards do red crabs face at sea? What hazards do they face on land?
  
  Show Answer
  
  At sea, red crabs risk being swept away by the currents or eaten by predators. On land, red crabs must survive predators such as the yellow crazy ant.
Articles & Profiles
- National Geographic Magazine: Animal Migrations
Audio & Video
- National Geographic Channel: Red Crab Marathon
Websites
- National Geographic Animals: Migrations Quiz
- National Geographic Animals: Red Crab

Term	Part of Speech	Definition	Encyclopedic Entry
animal migration	Noun	process where a community of animals leaves a habitat for part of the year or part of their lives, and moves to habitats that are more hospitable.
burrow	Noun	small hole or tunnel used for shelter.
crab	Noun	type of marine animal (crustacean) with a flat body, hard shell, and pincers.
hatch	Verb	to emerge from an egg.
hazard	Noun	danger or risk.
Indian Ocean	Noun	one of Earth's four oceans, bordered by Africa, Asia, Australia, and Antarctica.
instinct	Noun	natural motivation or behavior.
larva	Noun	a new or immature insect or other type of invertebrate.
lunar cycle	Noun	complete cycle of visible phases of the moon, approximately 29.5 days.
migration	Noun	movement of a group of people or animals from one place to another.
ocean	Noun	large body of salt water that covers most of the Earth.	Encyclopedic Entry: ocean
plateau	Noun	large region that is higher than the surrounding area and relatively flat.	Encyclopedic Entry: plateau
predator	Noun	animal that hunts other animals for food.
rain forest	Noun	area of tall, mostly evergreen trees and a high amount of rainfall.	Encyclopedic Entry: Rain forest
tide	Noun	rise and fall of the ocean's waters, caused by the gravitational pull of the moon and sun.	Encyclopedic Entry: tide

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Editor

Caryl-Sue, National Geographic Society

Producer

Nina Page, National Geographic Society

Page Producer

Makayla Trotter

Last Updated

Jan. 19, 2012

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