The brightly-coloured Birgus latro, also known as the Coconut crab, or Palm Thief, can have an abdomen as large as a football and a powerful claw-span of up to one metre. It's the biggest known anthropod to live on land and is native to Indo-Pacific islands.
Researchers Steffen Harzsch and Bill Hansson from the University of Greifswald and the Max Planck Institute did not concern themselves with the crab's ability to sever a human finger effortlessly, they were interested in a more imperceptible skill – its sense of smell.
In 2008, the pair followed the movement patterns of Coconut crabs for three weeks on Christmas Island in the Indian Ocean.
“We noticed right away that the crabs moved purposefully over long distances to fallen fruit and Arenga palm fruits – an indication of a developed sense of smell,” 42-year-old professor Harzsch told news agency DDP.
The scientists followed this discovery with smell experiments sensory evaluation of the crabs' antennae, which also showed the crabs had developed excellent olfactory capabilities.
This ability is a sign that the crabs, which belong to the terrestrial hermit crab family, formed their smell phylogenetically – or due to evolution.
But a separate set of tests opened a whole new set of mysteries for the duo. To find out how dependent on water the crabs still are, the team conducted satellite surveillance on 20 specimens in the rainforest.
“At dusk the crabs followed a dedicated 3.5-kilometre route to the ocean,” Harzsch said.
Here they found freshwater pools in the crags, moistened their breathing organs, and returned to their dens following the same route.