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While we debate whether the durian is the best or worst food on the planet, it turns out this wonderful oddity requires healthy populations of flying fox for survival

Hundreds of people scramble for durians, often called ‘the king of fruits’, during the Durian Festival in Kuala Lumpur, Malaysia.
Photograph: Teh Eng Koon/AP

Durian. Depending on whom you talk to it’s either the most beloved or the most despised fruit on the planet. It suffers no moderation, no wishy-washiness. It is the king of fruits or the worst thing you’ve ever tasted. Due to its potent odour – delicate and sweet to its advocates and sewage-like to its detractors – durian has been banned from airplanes, subways, and hotels (though punishments appear light if non-existent). But a recent study in Ecology and Evolution finds there may be no durians at all without bats: big, threatened bats. The scientists found that flying foxes – bats in the Pteropus and Acerodon genus and the largest in the world – are likely vital pollinators for the polarising durian.

“We already knew that flying foxes feed on durian flowers, but there was this unsubstantiated belief, even among some researchers, that flying foxes just destroyed the flowers,” said Sheema Abdul Aziz, the lead researcher on the project that was done as part of her PhD at the Muséum National d’Histoire Naturelle in France. “It doesn’t help that a durian flower only blooms for one night, then falls off the tree naturally, regardless of whether it’s been pollinated or not. When people see all the flowers on the ground in the morning, they think it’s the bats.”

This sleepy Island flying fox may be key to safeguarding the world’s durians.

This sleepy Island flying fox may be key to safeguarding the world’s durians. Photograph: Sheema Aziz

It’s not. By setting up camera traps high in durian trees on Tioman Island off the coast of peninsular Malaysia, Aziz and her colleagues exploded the myth that flying fox were damaging the flowers. Instead, the researchers watched the large winged-mammals – in this case the Island flying fox – hang upside down over the flowers and bow down their long snout into them, lapping up the nectar while leaving the flower unruffled.

“The video footage showed without a doubt how delicately flying foxes feed without destroying the flowers, and it also showed how tough and hardy these durian flowers really are,” Aziz said, who is also the founder and president of Rimba, a local NGO devoted to getting hard science out to the government and the public.

Flying foxes may not be the durian’s only pollinator. Aziz said other bats – including smaller ones – have been seen pollinating durians. It is also possible that civets and slow loris are capable of pollinating durian in some parts of Asia. Still, that doesn’t mean all pollinators are equal. Aziz pointed to recent research in Thailand that found some bats are better pollinators than others depending on the plant species.

“This really suggests that the loss of a primary pollinator can potentially affect fruit production, even when there’s another, substitute pollinator that’s still available to do the job,” she said. “This is the sort of thing that I’m hoping to investigate further, if I can get funding to continue my research into durian pollination ecology.”

Camera trap video of a flying fox taking nectar from a durian flower.

But like so many species in Southeast Asia, flying fox populations are under assault. According to Aziz, hunting and killing bats as pests are the biggest threats to flying fox species across the region. In some places flying fox are killed to be eaten, in others for traditional medicine.

“I’ve even heard of trigger-happy people with guns using flying foxes for target practice, just for fun,” she said. “This all stems from the fact that people don’t value flying foxes as being important in any way – they’re only viewed positively when they’re dead and can be consumed.”

Of course, deforestation is also threatening bat populations. Southeast Asia has some of the highest deforestation rates in the world with Indonesia recently eclipsing Brazil as the world’s biggest forest destroyer.

Farmers will often kill flying foxes en masse viewing them as a pest, but Aziz says this could undercut the durian industry.

“If growers are killing the bats, this will actually reduce the production of durian fruits. So there’s a real economic implication there … Bat conservation should be a real priority for the commercial durian industry.”

Aziz stresses the situation is complicated as flying fox and other bats are also known to damage some fruit crops, so mitigation efforts need to be developed to protect particular crops from raiding bats – without killing them.

Governments have a major role to play here as well, according to Aziz, who says they need to extend legal protections to bats and their habitats.

“For flying foxes this means protecting rainforests, mangroves, and swamps,” she said. “Mangroves and swamps are the last few refuges sheltering flying foxes from hunting pressure, so their roost sites need to be secured.”

Globally, there are around 70 flying fox species – but six species have gone extinct in recent times: the small and large Samoan flying foxes, the small Mauritian flying fox, the dusky flying fox, the large Palau flying fox, and the Guam flying fox – all bats once found on islands.

Meanwhile, around half of the surviving flying fox species are considered threatened with extinction and many that are not are still imperiled locally.

The large durian flower requires equally large pollinators.
The large durian flower requires equally large pollinators. Photograph: Rimba

Bats are not just threatened by hunting and habitat loss, according to Aziz. They are also threatened by a reputation for being nasty, scary animals and associated almost solely with disease. She points out that nearly all the research on bats in her home-country of Malaysia has been around bat diseases – not their ecology or importance in maintaining food sources and forests.

“Even conservationists and scientists have largely ignored them here,” she said.

Aziz is changing that. When her study first landed, it produced a remarkable headline in the Malaysian Star: Dwindling flying fox numbers, dying durian industry. News stories were also carried regionally in the New Straits Times and the Malay Mail. Aziz, herself, appeared on a local radio programme.

“Flying foxes could be doing all kinds of pollinating jobs that we’re not aware of, just because we haven’t thought to look into it, or because we simply ruled them out without investigating it properly,” she said.

This is why research is so important. But next comes the really hard part: conservation. Conservation means convincing the government and the public that protecting species – and wilderness – matters. And then implementing new laws and measures on the ground.

But durian lovers should take note: your king of fruits depends on the king of bats. Lose one and we’ll lose the other.

Durian haters? Don’t worry: it’s likely more research will shows these bats pollinate far more than durian trees. Just take this example: Aziz believes flying fox are “likely” integral to the survival of the most important ecosystems on the planet: mangroves. Buffeting coastal populations from storms, storing massive amounts of carbon, and housing fish nurseries for innumerable species, mangroves are long-neglected wilderness powerhouses. And it may be that they – like durians – depend on bats.

Like many people – and even many biologists – Aziz says she never thought she would be working with bats. But then she got an HSBC-Earthwatch Fellowship to work with bat expert Tigga Kingston from Texas Tech University.

“Holding a tiny little fluffball with wings, and getting to see it up close and personal, was a life-changing experience for me,” she said. “I knew then that I wanted to study bats and help protect them.”

Scientist, Sheema Aziz, making her up the durian tree.