At first glance, its name might be confused for dish served by an overly-ambitious chef de cuisine in the Midwest: Coconut crab. But the reality is much weirder. It is perhaps the least fishy of Ugly Fish.
Coconut crab is actually a modern arthropod with ten legs that lives in the far-flung islands of the Pacific and Indian Oceans. In fact, it is the largest of any of the modern arthropods and may have reached the absolute size limit for arthropods with the current atmospheric pressure found on the Earth. Millions of years ago, it may have been bigger. They can weigh as much as 4.1 kg (9.0 lb) and grow up to 1 meter (3 ft 3 in) in length from leg to leg. Found on islands across the vast Indian Ocean and even more vast Pacific Ocean, it can be seen as far east as the Gambier Islands and as far west as Madagascar and Zanzibar, off the eastern shore of Africa. Its distribution matches that of the majestic coconut palm. There is evidence that they once inhabited Mauritius and the Australian mainland, where they are now extinct. They are sometime known as robber crabs: a tribute to their Latin taxonomic name Birgus latrus (Birgus the thief).
With their powerful claws, coconut crabs can crack open a coconut
Coconut crabs got their name for their penchant for climbing coconut trees and consuming the delicious contents of the nuts. They are uniquely capable of organizing themselves into pairs and trios to crack open coconuts to reveal the white and edible flesh inside. Visitors to places like the Cook Islands have the rare treat of seeing these huge crabs scuttling across the beaches and surmounting the towering palm trees there in search of food. Besides coconuts, these crabs eat such things as fruit, the pitch of fallen trees, and carrion. They also like an occasional crab meal. But they are also known to dine on mammals. More on that later.
As for coconuts, these crabs are champs. A coconut crab individual is able to remove the fibrous layer from a coconut on the ground, and then carry it in a claw and into a 30 foot tree. It then drops the husk and seeks the coconut meat inside. They then jump out of the tree to seize upon the tasty flesh.
They have adapted so fully to terrestrial life that in their adult form they will actually drown if immersed in water for as little as an hour. It is during their larval, planktonic stage that they are adept swimmers. After the male and female adults mate on land, the females run off to sea to lay down their eggs in the surf. Three to four weeks after being abandoned to their fate by the females, the planktonic larvae settle down on the sea bottom and seek out abandoned mollusk shells to occupy. They carry these much like hermit crabs do, and eventually migrate to the shore and do not return to the sea. They start mating at the tender age of 5 years, and can live into their 60s.
Coconut crabs climb trees to find their treats
Coconut crabs cannot swim. Over the millennia, they have developed a branchiostegal lung that allows them to breathe the free air. A mid-way stage between gills and lungs, the branchiostegal lung bears some similarity to gills but is adapted to absorb oxygen from the air, rather than the sea. The crabs use their hindmost, smallest pair of legs to clean their lungs and keep them moist. Since the lungs require water, the coconut crab strokes its wet legs over the spongy branchiostegal tissue. Sometimes, the crabs drink water they find on land and transfer from its larger legs to the smaller ones.
Another significant adaptation the coconut crab has made is its acute sense of smell. Like other arthropods, coconut crabs have organs called aesthetascs on their antennae to determine both the concentration and the direction of odors. Since they live on land, the coconut crabs’ aesthetascs resemble those found among insects: evidence of parallel evolution. They can sense tasty food over long distances.
Coconut crabs can live more than 60 years
Juvenile coconut crabs wear mollusk shells or remnants of coconuts to shield themselves, especially their soft underbellies. As they grow, they seek out larger shells and eventually in water. As with all hermit crabs, they change their shells as they grow. Eventually, their abdomens harden so that they no longer require wearing a shell. They continue growing throughout life.
Christmas Island in the Indian Ocean is known for having the largest and densest population of coconut crabs in the world. But they are outnumbered by the prolific by more than 50 times by the Christmas Island red crab, Gecarcoidea natalis. Other Indian Ocean populations exist on the Seychelles, including Aldabra and Cosmoledo, but the coconut crab is extinct on the central islands. Coconut crabs occur on several of the Andaman and Nicobar Islands in the Bay of Bengal near India. They occur on most of the islands, and the northern atolls, of the Chagos Archipelago. Large populations are found in the Cook Islands in the Pacific.
Coconut crabs live solitary lives in underground burrows and rock crevices that they have dug for themselves. During the hot hours of the day, they chill out in their self-made caves where they rest on beds made of coconut husks.
Coconut crab feast in the Cook Islands
The coconut crab is eaten by Southeast Asians and Pacific Islanders, who enjoy it as a delicacy that has supposed aphrodisiacal properties. Intense hunting has made the tasty crustacean an endangered species in some places, and extirpated it elsewhere. While it is delicious, if a coconut crab has eaten certain things, they can be toxic.
Oh, before I go, a word on the carrion-consuming habits of coconut crabs.
In November 2010, expedition leader Richard Gillespie announced that he had found evidence of the final resting place of iconic aviatrix Amelia Earhart. According to Gillespie, she probably died on an atoll called Nikumaroro in the Republic of Kiribati: a remote group of islands in the Pacific Ocean. She crashed, along with her navigator, on July 2, 1937. They may have survived the crash for a time.
Gillespie, author of the book "Finding Amelia," sought to solve the mystery of where Earhart and navigator Fred Noon may have crash-landed. What they found was gruesome. All they found that could be associated with the ill-fated flight was a woman’s shoe, an empty bottle, and a box that once contained a sextant with serial numbers consistent with the type used by Noon. Basing his hypothesis on a similar case, Gillespie suggested that when the Earhart and Noonan died, opportunistic coconut crabs may have devoured their flesh and then hid their bones in burrows beneath the surface of the isolated atoll. "The reason why they found a partial skeleton is that many of the bones had been carried off by giant coconut crabs. There is a remote chance that some of the bones might still survive deep in crab burrows," Gillespie said.
Thus, coconut crabs added a wrinkle to an aeronautical mystery and another chapter to culinary history.
Described by Leach in 1816
Species: B. latro
Binomial name: Birgus latro