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The COVID-19 pandemic has brought the spread of zoonotic diseases to the fore, with evidence mounting that bats infected another animal, an ‘intermediate host’, perhaps pangolins, which subsequently transmitted the virus to humans. Endangered bats are being culled in China and Indonesia, among other places, in a misguided attempt to stop the spread of the coronavirus, but their importance in their ecosystems cannot be stated enough. 

With the rise of zoonotic diseases, most recently COVID-19, bats are increasingly being viewed with fear and disgust around the world. However, they offer us numerous important ecosystem services, ranging from food and medicine to tourism, but in particular, pest control and pollination. Their image also exposes the deeply ingrained problems of speciesism, creating the perception that bats are spreading diseases to humans instead of humans catching diseases from bats- a minor, but important, nuance. What benefits do bats bring to their ecosystems?

Bats are the only mammal that can fly, allowing them to spread from one community over a wide area. This means they can harbour a large number of pathogens. Flying also requires a huge amount of activity for bats, which has caused their immune systems to become very specialised.

Andrew Cunningham, Professor of Wildlife Epidemiology at the Zoological Society of London, says, “When they fly they have a peak body temperature that mimics a fever. It happens at least twice a day with bats- when they fly out to feed and then they return to roost. And so the pathogens that have evolved in bats are able to withstand these peaks of body temperature.”

This could present a problem when these diseases cross into another species. In humans, a fever is a defense mechanism designed to raise the body temperature to kill a virus. A virus that has evolved in a bat will likely not be affected by a higher body temperature.

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COVID-19 has been framed as a virus which bats spread to us- we are the victims. However, this could not be further from the truth. COVID-19, or many other zoonotic diseases, did not spread to humans because animals venture into our territory. It is us infringing on the natural habitat of animals that results in us catching these zoonotic diseases. We are not the victims, but the instigator. 

How are these zoonotic diseases spread? When bats are stressed- by being hunted, by being kept in wetmarkets or having its habitat damaged by deforestation- its immune system is challenged and finds it harder to cope with the pathogens it harbours.

Cunningham says, “It would allow infections to increase and to be excreted- to be shed. You can think of it like if people are stressed and have the cold sore virus, they will get a cold sore. That is the virus being ‘expressed.’ This can happen in bats too.”

Vampire bats were culled in Peru during the 1970s to control the transmission of rabies- an act driven by fear and a lack of knowledge about the disease. However, culling tends to target the adult vampire bats, who are immunised to the disease, as compared to juvenile ones, who are not immunised. This can cause rabies to be more prevalent within the bat population and ironically increases our likelihood of catching rabies from the bats.

Such events highlight the prevalence of speciesism, the idea that being human is a good enough reason to have greater moral rights than non-human animals. 

Bats are not harbingers of death, but hold an incredible importance in the ecosystems they inhabit. In these precarious times, animals should not suffer further at the hands of humans because of paranoia. As Sir David Attenborough says, “It’s extraordinary how self-obsessed human beings are. There is so much more out there than what connects to us”. The knowledge and awareness of our bigoted views towards animals is essential for our proper coexistence with nature. 

Why are bats important?

Importance of Bats: Pest Control

Bats eat insects which are considered pests to humans. Insects make up two-thirds of bats’ diets and they are able to consume (at least) a quarter of their body mass in insects nightly. This ferocious appetite is important in protecting crops, making bats an essential part of the global food system. In Indonesia, the exclusion of bats could cause up to a 30% decrease in cocoa harvests. Without them, many of the crops meant for us would be eaten by insects instead. Other indirect benefits, including the ecological benefits of not using pesticides, must also be considered. 

Additionally, bats devour those pests that harm our health. Bats are famous for their mosquito hunting prowess. While mosquitoes do not directly kill humans, they are hosts for many diseases such as Malaria, Dengue fever and Zika virus. It is estimated by the World Health Organization that 725 000 people die of mosquito-borne diseases annually. As the natural predator of insects, including mosquitoes, bats help to control the mosquito population, protecting our health in the process. 

Importance of Bats: Pollination 

While some bats prey on insects, others feast on fruits and nectar. In many cultures, bats are seen as agents of death. To the many plants that rely on bats to pollinate their flowers and disperse their seeds, this is the polar opposite. Such plants include agave, durian, wild bananas, breadfruit and mango. Durians are exclusively pollinated by bats. They do so by producing odours that attract bats and hanging their flowers upside down to make it more accessible for them. Without bats, this $17.6 billion industry would likely not exist. Not only do bats increase the quantity of fruits, they can also influence its quality. Pitaya, also known as dragon fruits, are found to be less sweet and heavy when not pollinated by bats. The implication is significant. Even if we are somehow able to mimic the pollinating role of bats, the fruits we harvest would still be inferior. Overall, bats pollinate around $200 billion worth of crops, which represented around 10% of the world food crop production in 2005.

This virus makes it clear that anthropogenic environmental damage can kill humans fast. We must rethink the way we interact with and value nature to avoid another zoonotic spillover that affects the planet as drastically as COVID-19. This must be done through ceasing deforestation and wetmarkets and learning to live with nature in a more sustainable manner. 

2020 has so far seen swarms of locusts invading parts of East Africa, decimating crops and threatening food security, as well as bats in Australia, threatening the population with diseases. Is the climate crisis exacerbating these occurrences? 

Thousands of bats have invaded the town of Ingham in Queensland, Australia. The swarms of bats now outnumber the human population by thousands, creating fear among the town’s inhabitants; bats can cause lyssavirus, a rabies-like disease caused through bites and scratches. The town wants to get rid of the bats, however they are protected under Queensland law. 

Bats are known to carry many diseases, such as Ebola, SARS, MERS and the Marburg virus. While the animal acts as a natural reservoir for the illnesses, they do not get infected themselves. This is because the body temperature of the bat is maintained at around 40 degrees Celsius, too high for the viruses to activate. Scientists that have conducted research on the special immunity system of the bat have documented that some species can live up to 40 years, rare for an animal of its size. 

Because they can fly, bats are found all around the world and are able to adapt to both tropical and temperate climates. They reproduce quickly and it is estimated that one in five mammals are bats. 

Bats rarely spread viruses directly to humans, but can do so through biting. Most of the time however, they need an intermediate host. For example, it has been found that the masked palm civet was the intermediate host of the SARS outbreak in China and camels were found to be the intermediate host of the MERS virus in the Middle East. 

However, culling bats is not the answer. Bats are important pollinators in the tropics; many fruit tree species such as the durian have a specific species of bat as a pollinator. Bats are also an important keystone species that control the population of insects. 

The Implications of Climate Change for Bats

Researchers in Australia are still investigating the unusually large swarms of bats in Ingham. One hypothesis posits that the bats are looking for a suitable habitat to set up their colony after theirs was destroyed in the bush fires. 

How the Climate Crisis Exacerbates Harmful Swarms of Animals
An illustration showing the relationship between animals and humans in the spreading of viruses (Source: WhatsOrb.com).

Meanwhile, swarms of locusts invading East Africa have spread south to Uganda and Tanzania, threatening the already-fragile region’s population who already suffer from malnutrition with further food insecurity. Farmers and authorities have used drones and motorised sprayers to mass spray crops with pesticides, which are harmful to people. Additionally, insects could evolve to become pesticide-resistant. Farmers should rather use biopesticides such as fungus and bacteria, which are as effective but less harmful to humans. 

Climate scientists have said that unusually heavy rains brought by a cyclone off Somalia in December caused the deserts of Oman to become wetter than usual, conditions which provide favourable breeding grounds for locusts. This causes the usually solitary form of locust, the grasshopper, to develop group behaviour. This process, called ‘gregarisation’, is triggered by the signalling of pheromones from physical contact of each individual grasshopper. 

This change from solitary to group behaviour usually follows a period of drought and vegetation flushes after periods of rainfall. The locusts reproduce very quickly and a single swarm can span up to 1 200 square kilometres and can contain more than 80 million locusts per square kilometre. 

As the climate changes, weather patterns have become less predictable. In East Africa, there is usually one cyclone that makes landfall each year but there has been an increase in the frequency and intensity of the cyclones in the Indian Ocean. This change in precipitation may lead to more frequent locust invasions. 

Another factor contributing to increasing locust invasions is the reduction of the natural enemies of locusts, such as wasps, birds, reptiles and bats. This is due to deforestation and habitat destruction in East Africa. 

Meanwhile, a study in Europe has shown that insect populations have significantly declined by up to 80% in two decades in what is being called an ‘insect apocalypse’. The study looks at the number of insects hitting car registration plates, called the ‘splatometer’. This method is able to sample the number of insects in a large geographical range. 

The study coincides with the significant decline in worker bee populations observed around the world. The overuse of pesticides and destruction of habitats are the main causes for the reduction in insect numbers. Insects, especially bees, serve a vital ecological function for humans, including pest control and pollination. More diversity of insects means that ecosystems are better able to withstand external pressure. 

As we have entered the Holocene Extinction period, also known as the Anthropocene Extinction period, the number of species becoming extinct due to human activity is predicted to increase. It will eventually reach a tipping point and cause a cascade effect, further disturbing ecosystems and increasing the likelihood of swarms of animals invading regions. 

Featured image by: Adam Baker

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