The workers on the chocolate plantations of São Tomé used to refer to the cobra-preta as Homem mordido, homem perdido, meaning ‘man bitten, man lost’. Historical accounts of the snake tell tales of people jumping out of palm trees and falling to the ground, just to avoid being bitten by the infamous cobra-preta.
Until recently, the cobra-preta, meaning black snake in Portuguese, was believed to be the forest cobra (Naja melanoleuca), an invasive species brought over from mainland Africa. New research conducted in 2017 has disproved this theory. The cobra species found on São Tomé has been redescribed as the cobra-preta (Naja peroescobari), an endemic species to the Atlantic Ocean island of São Tomé. The snake was described by Luis Ceríaco, the chief-curator of the Natural History Museum of the University of Porto in Portugal.
Historical accounts of the snake also suggest it is a native species to São Tomé. “I was going through a 1540’s account of the snake written by a Portuguese sailor and the report clearly states the black snake was not an introduced species as was previously believed,” says Ceríaco. A genetic study was then completed in 2017. The appearance and molecular data collected on the snake also prove that the cobra-preta was not an invasive species. “Bringing together historical evidence and modern genetic testing was a really cool experience,” says Ceríaco.
The cobra-preta is mostly found in Obô Natural Park and appears to be absent from the savannah type areas in the northwest of the island. It seems to prefer shady moist habitats. “It is really rare to find a top predator, like the cobra-preta, endemic to a small island,” says Ceríaco.
The difference between cobra-preta and the forest cobra from the Congo rainforest
True to the nature of wildlife endemic to islands, the cobra-preta is larger than the mainland forest cobra. It can grow about 2m long. Evolution on islands results in dwarfism and gigantism among species, for example, the São Tomé dwarf olive ibis (Bostrychia bocagei) and the São Tomé giant treefrog (Hyperolius thomensis). The cobra-preta has fewer white markings around its neck than the forest cobra, also referred to as the white-lipped cobra. There is a slight colour difference between the species.
São Tomé and Príncipe becoming environmentally conscious
São Tomé and Príncipe are becoming increasingly eco-conscious and there has been a strong focus on removing alien invasive species. Researchers are also focusing on understanding and protecting other endemic species like the Obô giant snail for example.
“Researchers have been reviewing the identity of São Tomé and Príncipe’s terrestrial fauna and have found that most of the species on the islands are endemic, even if they are closely related to mainland species,” explains Ceríaco. Cobra-Preta is an example of this. “Sooner or later, without proper taxonomic recognition, cobra-preta would have been eradicated as part of a conservation project,” says Ceríaco.
Although no formal studies have been done on its diet, it appears cobra-preta feeds on truly invasive species like the least weasel (Mustela nivalis) and the black rat (Rattus rattus). “At least they are doing their bit to control invasive species,” says Ceríaco. It was previously believed cobra-preta was brought over by the Portuguese plantation owners to control rats.
How did cobra-preta get to São Tomé?
“This is the million dollar question,” says Ceríaco, “not only for cobra-preta but for all endemic species found on São Tomé and Príncipe.” Most wildlife specialists believe ‘rafting’ could be the answer as to how many of the species arrived on the island.
‘Rafting’ is when large clusters of wood and debris from island-like structures in the rivers of Central Africa. These islands then act like canoes and get carried out to sea. Snakes, birds and skinks get trapped on these rafts that get caught in the Guinea Current and transported to the islands. “The species then establishes itself on the island and evolves independently from the original population,” explains Ceríaco. “After many generations, they become a new species.”
Threats to the cobra-preta
“The exact population figures are difficult to predict,” says Ceríaco “But it appears to be fairly common and is often found basking on roads across São Tomé.” Most Sãotoméans work in agriculture and come across the snakes in the field. Habitat destruction from agriculture has destroyed large parts of the snake’s range.
In some parts of São Tomé, cobra-preta is eaten as a delicacy. As relations between China and São Tomé improve, the arrival of Chinese workers might result in a surge of snakes being captured for traditional Chinese medicine.
Cobra-preta snakebites and venom
Many Sãotoméans kill the snake on sight. “It is understandable, as the cobra-preta is a very dangerous snake and the standard of hospitals in São Tomé is very poor,” says Ceríaco. Death from a cobra-preta bite can occur within hours.
It is believed that the venom of the cobra-preta is similar to the mainland species – a mixture of cytotoxic and neurotoxic venom. Cytotoxins have a toxic effect on cells in the area of the snakebite, while neurotoxins damage or impair the functioning of the nervous system.
Currently, the number of cobra-preta bites that take place each year are not recorded. “A study on the prevalence of snakebites on the island is needed,” says Ceríaco. Cobra-preta is the only venomous snake in São Tomé and Príncipe.
Snakes of São Tomé and Príncipe
All eight snake species found on São Tomé and Príncipe are endemic. The cobra-preta, the cobra-jita (Boaedon bedriagae), and São Tomé wood snake (Philothamnus thomensis) only occur in São Tomé.
The Fea’s beaked snake (Letheobia feae) and Newton’s beaked snake (Letheobia) are endemic to both São Tomé and Príncipe islands.
The sua sua (Hapsidophrys principis), elegant worm snake (Afrotyphlops elegans) and an undescribed species of brown house snake (Boaedon sp.) are only found on Príncipe. Ceríaco is collaborating with others to describe the brown house snake species.
The cobra-preta is one of many species from São Tomé and Príncipe found hiding in plain sight. Until recently it was believed the Príncipe thrush was a subspecies of São Tomé thrush.
Written by Georgina Lockwood
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