Every year up to 100 million red crabs inhabiting Australia’s Christmas Island migrate from their forest home to the Indian Ocean. This convoy of crustaceans travels 9 km (5 miles) with one sole goal – reproduction.
The crabs are making their way to the sea. Mating takes place on the shore because the larval form of the crab has primitive gills that function only in water. Female crabs release eggs into the sea. The larvae hatch and grow in the water for about a month before congregating at the shore, ready to become mini air-breathing crabs. The tiny baby crabs then head back to the forest.
Another huge concentration of creatures can be found at Bracken Cave in the USA, home to the world’s largest bat colony. About 20 million bats exit the cave every day at dusk searching for insects to feed on – one of nature’s most amazing aerial sights.