An expedition to the forests of Sierra Leone, West Africa, revealed two species of crabs new to science and two species not seen in more than half a century. The research team found an Afzelius’s crab (Afrithelphusa afzelii), which has had no recorded sighting for 225 years (since 1796), and the Sierra Leone crab, not seen in 66 years. Also found were two species of crabs belonging to the genus of the common river crab in West Africa. 

On a recent expedition to the remote forests of Sierra Leone, West Africa, researchers found two species of crabs new to science and rediscovered two species not seen in more than half a century.

For 23 days, Pierre A. Mvogo Ndongo, a researcher from the University of Douala in Cameroon, trekked through remote rainforests in search of the Sierra Leone crab (Afrithelphusa leonensis), a unique purple-clawed land crab that has not been spotted by scientists since 1955.

“It was not easy,” Mvogo Ndongo said in a press release. “This trip was very, very difficult. You have to be psychologically strong. But I was very determined.”

On his journey, Mvogo Ndongo asked locals if they had seen crabs that live on land, far from permanent water sources. Two men in Moyamba district described colorful crabs living nearby and led him to a farm bordering the forest. Within three days, Mvogo Ndongo and his team found an Afzelius’s crab (Afrithelphusa afzelii), which has had no recorded sighting for 225 years (since 1796). Over the next few days, the researchers found many of the orange-legged, purple-bodied crabs in that area, indicating the presence of a healthy local population.

In early 2021 the Afzelius’s crab (Afrithelphusa afzelii) was spotted by scientists for the first time since 1796. Photo by Pierre A. Mvogo Ndongo courtesy of re:wild.

The team then traveled to Sugar Loaf Mountain in Western Area National Park in search of their target species, the Sierra Leone crab. The spread of COVID-19 and looming lockdowns meant that their time was limited.

“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,” Mvogo Ndongo said. His team excavated burrows using tools, working carefully not to hurt the crabs. “When I found the Sierra Leone crab, I was very, very happy. This was after almost three weeks of searching for lost species.”

Male Sierra Leone crab rediscovered near Freetown. The species has been missing to science since 1955. Photo by Pierre A. Mvogo Ndongo courtesy of re:wild.

African land crabs are unique; only five species are known to exist. Compared to their water-dwelling relatives, these land crabs are more colourful and live in burrows, rock crevices, and trees away from permanent water sources. They use specialised lung-like structures to breathe air, and some even climb trees.

The team also found two species of crabs previously unknown to science, in the genus Liberonautes, or the genus of the common river crab in West Africa. Only one species of this genus was known to exist in Sierra Leone before now.

Describing and naming these species will require detailed morphological examination, DNA sequence comparisons and specialist expertise, but the process is currently on hold due to COVID-19 travel restrictions.

You might also like: 12 of the Most Endangered Animals in the World

Neil Cumberlidge, a professor at Northern Michigan University who worked with Mvogo Ndongo on the expedition says they are optimistic about finding healthy populations of both of the “lost” species of crabs. However, the forests in which the crabs live, part of the Upper Guinea Forest block, face threats.

“These forests are under immediate threat through deforestation, at large and small scales, ultimately driven by the expanding human population in West Africa,” Cumberlidge told Mongabay. “Even the Western Area Peninsula National Park where the Sierra Leone crab was rediscovered is not as protected as it should be.”

The researchers plan to work with the IUCN’s Freshwater Crab Specialist Group to assess crab populations in the area. Once more is known about the numbers and locations of the crabs, scientists will develop a species-specific action plan that may include breeding programs, community education, habitat protection, and other efforts to protect and revive their populations.

“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 told Treehugger.

“What makes them vulnerable to extinction is their rarity,” Cumberlidge told Mongabay. “They are both narrow range endemic species, found in just a small area and nowhere else in the whole world, which makes them both hard to find and vulnerable to threats that could wipe them out completely. “

The quest for crabs was sponsored by the conservation organisation Re:wild, as the Sierra Leone crab is number eight on Re:wild’s 25 most-wanted lost species list.

So far, Re:wild’s Search for Lost Species program has rediscovered seven other lost species, including the Wallace’s giant bee and the velvet pitcher plant in IndonesiaJackson’s climbing salamander in Guatemala; the Somali sengi in Djibouti; the Voeltzkow’s chameleon in Madagascar, and the Fernandina giant tortoise in the Galápagos.

The first scientific documentation of a live Somali Sengi, one of Re:wild’s “rediscovered” species. Photo by Steven Heritage, Duke University Lemur Center.

“It’s important to understand if [a species] truly has been lost or not, because once we know if it’s still out there, we can set into motion the proper plans and action steps that will hopefully conserve that species,” Nikki Roach, associate conservation scientist for Re:wild, told Mongabay.

“[It] also gives us a glimmer of hope. It shows that species can persist despite all the pressures that they’re facing … There’s still hope that we can turn things around. And with the proper conservation action, proper protections of habitat, and engagement in the local communities, we can actually still save species. And I think that is a positive, hopeful message that the public needs to hear.”

Featured photo courtesy of Neil Cumberlidge.