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