Colorful 'Lost' Crab Rediscovered After 66 Years

The Sierra Leone crab is very unusual in the world of crabs. It’s extremely colorful with purple claws and a bright body. It doesn’t spend very much time anywhere near the water. Instead, it lives in rock crevices or climbs trees to live in burrows. Some live in marshes or on the forest floor.

And, until recently, most scientists weren’t even sure these elusive animals even still existed.

Researchers spent weeks earlier this year in West Africa in search of the crab, which hasn’t had a confirmed sighting since 1955. It was rediscovered near Sugar Loaf Mountain in a national park in Sierra Leone.

The expedition was supported by Re:wild, an organization launched this year by a group of conservation scientists and Leonardo DiCaprio, a longtime supporter of environmental and conservation issues. Re:wild’s mission is to protect and restore the biodiversity of life on Earth.

As part of that goal, the organization is searching for the top 25 “lost” species. Those are animals with unverified sightings and scientific data which are enough to lead researchers to believe that they still exist.

The Sierra Leone crab (Afrithelphusa leonensis) was the eighth species on Re:wild’s 25 Most Wanted Lost Species list to be rediscovered.

“Most freshwater crabs in Africa live in rivers, streams and lakes, and only a few species live in more obscure habitats away from water because they can breathe air as well as water, just like land crabs. These freshwater crabs, however, are few and far between,” Neil Cumberlidge, a researcher and biology professor at Northern Michigan University who worked with Mvogo Ndongo on the expedition, tells Treehugger. Cumberlidge was unable to go to Sierra Leone because of the pandemic, so he had to consult via email.

“Only a few species are known, but those that are do not disappoint because they are extremely colorful compared to their river living cousins, and climb trees, live in rock crevices, marshes, or in burrows on the forest floor all well away from permanent water. Sierra Leone, Guinea, and Liberia and the only countries in Africa where these crabs occur, and there are only five species known, all rare.”

Chasing Leads from Locals

Pierre A. Mvogo Ndongo, a lecturer and researcher at the University of Douala in Cameroon, traveled to Sierra Leone, in West Africa, in search of the crab. He searched for more than three weeks from mid-January to early February throughout the northern, southern, and southeastern provinces of Sierra Leone.

Mvogo Ndongo interviewed people in the community, asking them if they had ever spotted crabs in the forest that lived far away from permanent water sources.

“The three weeks in Sierra Leone were very difficult as I spend about two weeks without finding the most wanted crab, I was looking for, despite all the strategies put in place,. But, only the common crab," Mvogo Ndongo tells Treehugger.

"Nevertheless, I kept my psychology strong and multiply strategies in parfait collaboration with Neil Cumberlidge. I was frustrated only about the global pandemic that getting worse at the moment I was in Sierra Leone."

He was able to get a lot of local young people interested in his research, he says, and convinced them of the benefits of getting involved in conservation projects. They helped them interview people in local dialects.

"After many false leads and a lot of tactics changed, I met two young men in the Moyamba District and described to them the vibrant colors and unique behaviors of the crabs," Mvogo Ndongo says.

They directed him to a forest outside of Freetown where he discovered a seemingly healthy population of Afzelius’s crabs (Afrithelphusa afzelii), another land-living crab that hasn’t had a documented sighting since 1796. 

A day later, after getting permission from local chiefs and the park manager, he searched within the Western Area National Park in the forests on Sugar Loaf Mountain.

Mvogo Ndongo and his team had to excavate some burrows using a pick and machete, working carefully so they wouldn’t harm the crabs. When they cleaned the dirt from the crabs, they saw the brightly colored bodies and knew they had found the first living specimens seen since 1955.

“In the four days searching the dense forests on Sugar Loaf Mountain, I was able to find six specimens of the Sierra Leone crab because I was able to recruit local people to go into the forest and search with me,” says Mvogo Ndongo. “When I found the Sierra Leone crab, I was very very happy. This was after almost three weeks of searching for lost species.”

Next Steps

Discoveries like these are important, yet bittersweet, the researchers say.

“These discoveries are important because we were thinking that both of these species might actually be extinct, because they had not been seen for many years (centuries in one case),” Cumberlidge says.

“It is bittersweet because the joy of discovering lost species is mixed with the realization that while not extinct, they are both critically endangered species on the edge of extinction, and that urgent conservation interventions will be required to protect these species in the long term.”

Cumberlidge is the chair of the International Union for Conservation of Nature (IUCN)’s Freshwater Crustacean Group, a team of international specialists interested in the conservation of freshwater crabs, shrimps, crayfish, and aeglids (freshwater crustaceans) and Mvogo Ndongo is a member of the group. They create and manage the IUCN Red List for those species and assess their extinction risks.

“The new data generated by the expedition, such as more detailed information on habitat, ecology, population status, and threats, will allow us to reassess the Red List status of each of these species (this will likely be Critically Endangered, i.e., close to extinction),” says Cumberlidge.

“The next step is to devise a Species Action Plan detailing exactly how this will be done, and then implement protective measures in the field together with Sierra Leone conservationists.”