Forget cats, forget traps — bring in the puff adders to revolutionise pest control

Daily Maverick

2 days ago

Africa's coolest pest control agents have fangs, no overheads and a killer instinct.
Enter the puff adder (Bitis arietans) — nature's unassuming, cold-blooded rodent regulator. A new study by Professor Graham Alexander at the University of the Witwatersrand has revealed just how spectacularly efficient these snakes are, offering compelling evidence that they might be the farmers' unsung ally.
They're often cast as villains, coiled and hissing in the corners of bushveld myths, but puff adders are ecological rockstars with a lazy flair for lethal efficiency. Unlike mammals who must eat constantly to fuel their furnace-like bodies, puff adders can down tools — or fangs — and wait. For months. Even years.
In the largest-ever study of its kind, Alexander raised 18 puff adders over four years under tightly controlled conditions. The snakes, all born in captivity, were housed at Wits University and observed during a series of trials that measured their feeding, fasting and weight changes. What he discovered could change the way we think about snakes — and pest control.
'The key idea,' Alexander explains, 'is something I called the 'factorial scope of ingestion'. It's a way of measuring how much more a predator can eat when food becomes abundant. No one's used this in animals before — I made up the name.'
Masters of the buffet
Turns out puff adders are masters of the buffet. During peak feeding periods, the snakes increased their intake by twelve times their normal dietary needs. One snake even ballooned to more than 2kg, more than double its starting weight. That level of flexibility is practically unheard of in mammals, whose metabolic needs keep them on a tight leash.
Let's translate: if puff adders were people, they'd gorge through the holidays on a dozen Christmas dinners, then not eat again until December. And they'd still be fine.
These findings, published in Scientific Reports, debunk the long-held idea that snakes, being ectotherms with slow digestion, have little impact on prey populations. Not only can puff adders gobble up rodents at astonishing rates when prey is abundant, they can also wait out the lean years, lying low with metabolic grace.
'I estimate that some of these snakes could fast for over two years and still survive,' Alexander says. 'When rodents boom, puff adders switch on, consuming mice week after week. But when the prey disappears, they simply… switch off.'
This ability offers a significant advantage over warm-blooded predators like mongooses or jackals, which must eat regularly or perish. Puff adders, with their secretive ways and ambush tactics, are perfectly adapted for ecological boom-and-bust cycles. They're like the ultimate freelance exterminators — no contract, no complaints.
But there's more. By staying put and waiting for rodents to scurry by, puff adders mount what ecologists call a 'functional response' — an immediate adjustment in feeding and breeding rate based on prey availability.
In the dusty corners of barns and the grassy fringes of maize fields, puff adders lie in ambush. And while their approach may be passive, the effect is anything but.
'Simple. Effective. Immediate.'
'When rodent numbers go up,' says Alexander, 'more rodents run past the snakes. And the snakes just eat more. Simple. Effective. Immediate.'
Puff adders, the study suggests, act as ecosystem stabilisers — naturally damping down the rodent population explosions that wreak havoc on crops. And because they don't need frequent meals, their populations don't crash during the quiet years, like mammals often do.
That alone should earn them some farmyard respect. But old fears die hard. Puff adders are responsible for the highest number of serious snake bites in Africa, due to their camouflage and tendency to stay still when threatened. But this reputation needs a rethink. According to data at a hospital in KwaZulu-Natal, the fatality rate from puff adder bites is extremely low. In one study of nearly 900 hospitalised snakebite cases, not a single death was recorded.
Still, Alexander admits he's been on the sharp end of a puff adder's fang.
'About 25 years ago I got bitten on the leg,' he says. 'It put me in ICU for nine days. But the real issue was the antivenom. I'm violently allergic to the horse serum it's made from — it stopped my heart.'
It's a sobering reminder of the risks. But it hasn't dampened his enthusiasm.
'Some people say working with venomous snakes is heroic,' he laughs. 'Others say it's just stupid.'
Each of the 18 snakes in his colony had its own personality, he adds — some were curious, others reclusive. This growing recognition of reptilian personality, even sentience, is changing how scientists view snakes.
Strategic and adaptive
'Snakes aren't mindless machines,' Alexander says. 'They're remarkable animals — strategic, adaptive and vital to the ecosystems they live in.'
So should farmers release puff adders into their barns? Not quite. Alexander cautions against artificially introducing snakes into new environments, which could disrupt local ecosystems.
'But if they're already there,' he says, 'don't kill them.'
With snake antivenom production faltering in South Africa, and rodenticide poisoning creating knock-on effects across food chains, the case for protecting natural pest regulators has never been stronger. Most bites, Alexander says, result from trying to kill them. They respond to threats.
Puff adders might not be cuddly, but they're efficient, low-maintenance, and — as Alexander's research shows — astonishingly good at their job. So next time you see a puff adder in your barn or near your wheat field, maybe hold off on the hoe. That fat, lazy, patterned lump might just be your best employee. DM