PHOTHARAM, Thailand – Bat caves smelled like bats.
In the darkness of the caves, in a cave complex west of Bangkok, Thais with headlights and lanterns took care of his business.
Pilgrims to the temple that owned the complex prayed to Buddha statuettes in one of the caves, the sculpted expressions of the statues revealing no reaction to the plip-plop-ploop of bat droppings falling on their shoulders.
Bat manure collectors, or guano, scraped the excrement to sell as fertilizer, lifting manure bags over a stalactite and stalagmite obstacle course.
And medical researchers, supervised by one of the world’s greatest bat virologists, captured the winged mammals to test them for traces of the coronavirus that causes Covid-19. Scientists believe it originated from bats.
Outside the complex, the abbot of the Buddhist temple, which calls itself the “temple of hundreds of millions of bats”, turned on a loudspeaker to tell visitors that the resident flying mammals were harmless.
“Don’t worry, these bats do not transmit disease because they are insect-eating bats,” said Phra Khru Witsuthananthakhun, the abbot. “Everyone knows that when bats eat fruit, they share it with other animals, like mice, and that’s how the disease spreads.”
The temple abbot is correct in saying that fruit-eating bats have been linked to serious viruses that have spread throughout the human population. But insect-eating bats have caused humans their share of deadly diseases. Many virologists believe that the horseshoe bat, an avid insect eater, may be linked to the coronavirus that causes Covid-19. And a report from the Thai national park identified a species of horseshoe bat in the caves.
The area around the caves, the Photharam district in Ratchaburi province, tied its luck to bats – attracting tourists, fertilizer companies and, most importantly, chiropterologists, scientists who study flying mammals.
In the tiny, vibrant heart of the local economy – some bats can vary their heart rate by 800 beats per minute – is the Khao Chong Phran Temple, which features the limestone caves where bats shelter during the day. In a single cave, there are three million bats of 10 different species.
Nearly a quarter of the world’s mammal species are bats, and their ability to fly while hosting a virus Petri dish makes them zoological wonders and efficient disease vectors. Infectious diseases believed to have arisen from bats in recent decades include coronaviruses like SARS and MERS, along with other viruses like Nipah, Hendra and Ebola.
Most of these viruses were transferred from bats to an intermediate host, such as a civet or camel, before reaching humans.
Although the coronavirus that causes Covid-19, which drew public attention in late 2019, has not been conclusively traced to bats in southwest China’s Yunnan province, a researcher has found evidence in horseshoe bats from a virus much like it. Cambodian horseshoe bat droppings also showed some links. And the same type of bat was the natural reservoir of the SARS coronavirus.
The discovery of the possible connection between horseshoe bats and Covid-19-linked coronavirus has led Dr. Supaporn Watcharaprueksadee, deputy head of the Center for Emerging Infectious Diseases in Thailand and a specialist in bat-borne viruses, to investigate whether bats in Thailand, which is not far from Yunnan and Cambodia, can share a similar viral load.
Dr. Supaporn said her team found no traces of a coronavirus similar to the one that causes Covid-19 in bats at Khao Chong Phran Temple, although other coronaviruses have been discovered there is. She also didn’t find horseshoe bats there.
Tests on humans residing in and around Khao Chong Phran, including guano collectors who spent decades close to bats, also found no evidence of antibodies to the virus.
However, the vision of researchers, dressed from head to toe with personal protective equipment, surprised a community that relies on bats as its economic mainstay.
“There is no Covid here,” said Auenjit Kaewtako, a district health volunteer who has been coming to Khao Chong Phran for 40 years. “Why should we blame bats?”
Although Thailand was the first country outside China to confirm a case of Covid-19 – on a Chinese tourist he visited last January – the nation appeared to have practically strangled local broadcasting since May. In general, Thais are aware of the use of face masks and the country’s borders have been closed to prevent the virus from reaching abroad.
But in recent weeks, the coronavirus has started to spread across the country after it was first identified in migrant communities working along the porous border with Myanmar. Thailand went from no local transmission cases in months to reporting hundreds of cases per day in late December and January.
Xenophobia increased, along with chirophobia, the fear of bats.
In the view of Khao Chong Phran’s guano collectors, who are not far from the border with Myanmar, the anxiety caused by bats is exaggerated. There are 17 species of bats in the area, and only two are fruit bats associated with the spread of disease, they say. The rest consume insects, which means that the bat droppings glow with iridescent residue from the insects’ wings.
“Even before my grandfather’s generation, we collected guano from the caves,” said Jaew Yemcem, 65, resting on the temple grounds with his bare feet nestled in soft bat dung mounds. “They were fine, and we are fine.”
Every Saturday morning, before dawn, Khao Chong Phran allows guano collectors, some using homemade balaclavas to protect themselves from manure drip, to enter the caves and explore the nitrogen-rich fertilizer. Many workers walk barefoot to better deal with slippery terrain with bat dirt and condensation.
After buying guano from collectors, the temple auctiones it off to farmers or agricultural intermediaries, who say that only a handful of the fertilizer added an attractive sweetness to guavas and an impressive circumference to papayas.
Collectors receive about 85 cents per bucket of guano and can accumulate a dozen buckets a day if they are lucky.
In some Southeast Asian countries, bats are appreciated for food. Although the temple tents in Khao Chong Phran already sold grilled bats, residents no longer eat them because they were designated as protected animals, said Supaporn, who has been researching bats in the area for a decade.
But Prangthip Yencem, who works as a cook assistant at a local school during the week and extracts guano on Saturdays, said bat consumption, while lower, continues. The bat tastes good in any type of preparation, she said, including sautéed with chile and holy basil or fried with garlic and white pepper.
For men, bat blood with an injection of alcohol is an invigorating cocktail, she said.
Residents of the area no longer hunt bats, as the abbot warned them against it, said Prangthip. But if a strange bat happens to fly on a telephone pole and fall to the ground, who would refuse a free meal?
“Even now, people eat bats,” she said, “and they don’t catch Covid.”
The bat population in the Photharam district has declined in recent decades, victims of the urban sprawl that is devouring rural Thailand. Heavy use of pesticides has also deprived bats of their food.
With fewer bats around, there is half the amount of guano collected a decade ago. The existence of fewer bats interrupted pollination patterns, damaging tropical ecosystems in a similar way to the decline of bees.
And, crucially, some bat virologists believe that an increase in stress among bats can make animals more vulnerable to the symptoms of the disease, possibly increasing the chances of viruses spreading to other species.
Normally, bats can live healthy lives with several viruses running through their bodies. But the gadgets of human development – tall buildings, electrical wires and cement stretches – can stress bat bodies while working overtime to use echolocation, pinging the sound frequencies to determine their surroundings.
Phra Somnuek, now a monk in the temple, recalls that when he was a child the sky darkened for more than two hours at dusk with the shadows of millions of bats coming out to feed at night. The flight of bats, still a tourist attraction, is now done in 45 minutes, he said.
“I am concerned that one day bats are just a legend here,” he said. “If we lose our bats, we lose what makes us special.”
Muktita Suhartono contributed reporting.