Black mambas could help to protect us by ringing poison alarm bells

Academic studies on nearly 100 black mambas in the Durban area suggest that these deadly snakes can potentially be used as a valuable sentinel species and biomonitoring tool, alerting health authorities to the presence of toxic metal pollution in big cities and industrial areas.

Professor Marc Humphries, an ecotoxicologist and environmental geochemist at the University of the Witwatersrand, notes that some snake species can be compared to canaries in a coal mine because their bodies and scales accumulate poisons from the animals they feed on.

With the assistance of Durban herpetologist and venomous snake handler Nick Evans, researchers from Wits, North-West University and the University of KwaZulu-Natal analysed tissue and scale samples from 61 live black mambas and 33 dead mambas to measure the level of four toxic heavy metals – arsenic, lead, cadmium and mercury.

Previous research, mainly in North America, has shown that birds, animals and some snake species can serve as valuable bioindicators of environmental pollution, but very little research has been done in Africa on the bioaccumulation of toxins in snakes.

The black mamba – an apex predator that can live for 20 years, mostly within a localised hunting territory – was seen as an ideal species to study in Africa.

Their results confirmed that these reptiles also accumulate heavy metals, not just in their organs and tissue, but also in their belly scales (providing researchers with a non-lethal method of collecting data by clipping small fragments of these scales using surgical scissors).

Humphries said one of the noteworthy conclusions from the study was the significantly lower levels of heavy metal accumulation found in mambas living in nature reserves and other green spaces within the city’s Durban Metropolitan Open Space System (D’MOSS).

In general, mambas captured in outlying areas such as Shongweni and along the north coast had much lower levels of heavy metals than those captured in the city or suburban areas.

The highest levels of arsenic and cadmium, and one of the highest lead measurements, came from a mamba captured in the Prospecton area south of the city, a heavy industry zone for the making of cars, metal products, paint and petroleum. Much higher levels of lead were also found in mambas around Queensmead, Escombe and Chatsworth compared with inner-city D’MOSS areas.

“Our findings support the hypothesis that snakes such as black mambas make ideal bioindicators for detecting patterns of heavy metal pollution in the environment and they can reveal patterns in pollution levels,” the researchers state in an article published in the Environmental Pollution journal.

Humphries said that while the research focused on the potential role of black mambas in monitoring environmental pollution, it also highlights the ecological value of Durban’s connected green spaces, which appear to buffer black mambas (and other urban wildlife) from potentially harmful pollution.

“The exciting thing is that we can get this information from a quick, harmless scale clipping,” he said. “It’s safe for the snake and could be used in cities across Africa (for similar biomonitoring).”

The researchers also hope that recognising the value of black mambas in monitoring environmental health may help to 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,” said co-author, Professor Graham Alexander.

Evans has also urged people to call in a snake expert to safely remove an animal from a property, should it pose a danger to residents or domestic animals, rather than killing them.

“Attempting to kill or capture a black mamba puts you at higher risk of being bitten. They are animals that just want to be left alone, in which case, they actually pose very little risk to humans,” he said. DM