Africa’s most feared snake can help to sniff out pollution
- Wits University
New research has shown that heavy metals such as lead, arsenic, cadmium and mercury accumulate in the scales of Black Mambas.
Black Mambas,
Africa’s fastest and most feared snakes, can be a key player into tracking pollution, while at the same time keeping ecosystems healthy.
New research from the University of the Witwatersrand in Johannesburg, South Africa (Wits University), has shown that heavy metals such as lead, arsenic, cadmium and mercury accumulate in the scales of Black Mambas (Dendroaspis polylepis).
The study, conducted on snakes captured in Durban in KwaZulu-Natal and published in Environmental Pollution, was the first of its kind to examine heavy metal accumulation in an African snake species. The results mean that researchers can use scale clippings from these snakes to accurately measure spatial patterns of environmental pollution levels, without harming the snakes.
“Black Mambas are common in the Durban area, and individuals often live in the same refuge for years,” says Professor Graham Alexander, a herpetologist at Wits. “If the body tissue of individuals contain high levels of heavy metals, it is a strong sign that the local environment is under threat.”
Snakes such as Black Mambas are Apex predators, which mean they feed on various other animals such as birds and rodents. The pollutants absorbed from the food that birds and rodents eat, eventually accumulate in the body tissue of Black Mambas.
The research team, led by Professor Marc Humphries, an environmental chemist at Wits, analysed scale clippings from live snakes that were removed from domestic, industrial and commercial properties by snake expert Nick Evans, from KwaZulu-Natal Amphibian and Reptile Conservation, and tissue samples from mambas that had died in road accidents or from human conflict. The snakes found in industrial and commercial areas had far higher metal levels than those from nature reserves and green spaces, such as Durban’s Metropolitan Open Space System (D’MOSS) network.
The study’s findings highlight the value of having connected green spaces around our cities, as they help protect wildlife from harmful pollution linked to urban development.
“We found a clear association between land use and heavy metal exposure in black mambas. Snakes living in connected green spaces around the city generally had significantly lower heavy metal concentrations in their scales compared to those in more industrial and commercial areas,” says Humphries.
“The exciting thing is that we can get this information from a quick, harmless scale clipping,” Humphries said. “It’s safe for the snake and could be used in cities across Africa where snakes are already being relocated from homes and businesses.”
Mambas as apex predators
The Black Mamba inhabits a wide geographic range in sub-Saharan Africa. In South Africa, its range is confined to the coastal regions of KwaZulu-Natal, and in the north-eastern parts of the country.
A second study in the Zoological Journal of the Linnean Society, also co-authored by Alexander, shows that Black Mambas are more than just top predators. They also shape their environment in ways that benefit other species.
Mambas often use the same refuge sites, such as termite mounds, hollow logs, and abandoned buildings for years. They serve a valuable role in the environment, by controlling rodent populations, which may help protect crops and reduce the spread of rodent-borne diseases.
Changing perceptions
Black Mambas appear to have been increasing in numbers in the Durban area over the last decades, with compared to historical data, with Evans removing steady numbers from suburban, industrial, informal settlements and rural areas. Evans gets between 100-120 calls a year for Black Mambas in the throughout the eThekwini Municipality.
“Humans often make their properties appealing to mambas by dumping rubbish over their fence, in their garden, having messy sheds or garages, creating rat breeding grounds,” says Evans. “Durban also has high numbers of feral cats, and mambas feed on their kittens. So there is suitable habitat and an abundance of food.”
Evans says unprovoked bites are extremely rare, with approximately 3 to 5 bites occurring per year.
“Almost all patients survive, unless they do not go to hospital. Some of the bites are dry bites, warning bites where no venom is injected.”
The team believes that recognising the value of Black Mambas could help shift public attitudes from fear to appreciation.
“People are understandably scared of mambas, as they are one of Africa’s most dangerous snakes, but if we treat them correctly, they can be a valuable tool to assess pollution levels,” says Alexander. “Snakes in general can play a valuable role as biomarkers for environmental health, and should preferably be left to live in peace in their natural environments.”
Evans urged residents to rather call a snake expert to safely remove an animal from a property, should it pose a danger to residents or domestic animals, rather than kill them.
“Experts can safely remove and relocate snakes where needed,” says Evans.
“Attempting to kill or capture a Black Mamba puts you at high risk of being bitten. Black Mambas are animals that just wants to be left alone, in which case, they actually pose very little risk to humans.”
Evans often remove snakes from situations where bites could easily have occurred, but they’d rather sneak past people or hide, rather than choose conflict.
“Snakes play an extremely important role in nature and should be protected as much as possible. They are excellent for rodent control, and aid in the control of Rock Hyrax populations.”
Domestic pets like dogs are normally an issue, as they attack snakes.
“Please keep dogs away from all snakes, especially Black Mambas, should you see the snake before your dog.”