Bats first showed up in the fossil record around 50 million years ago, living in a time where whales had not yet evolved their flippers, and ants the size of hummingbirds roamed freely. Although, it is believed bats existed much earlier in prehistory, as bat fossils dated 50 million years show signs of diversification which only occurs when the main species is already established; which takes hundreds of thousands of years. Today, there are over 1,000 different species of bats; nearly one in four mammal species is a bat. And each species is incredibly diverse; from the ‘Flying Fox’, an impressive two-foot-tall bat with a four to a six-foot wingspan that weighs a mere two to four pounds, to the ‘Bumblebee Bat’, which stands at a meager height of two inches, has a wingspan of six inches and weighs less than two grams.
The scientific name for bats is Chiroptera, which is Greek for ‘hand wing’ due to their four long fingers that connect to each other by a thin layer of skin to form wings. This makes bats the only mammals with the ability to fly. Because these wings are still hands with thumbs that are not connected to the wing, they are exceedingly mobile, able to pick fruit apart, climb rough trees, and walk across the forest floor. The thin, flexible skin membrane of bat wings also makes them exceedingly agile, able to turn quickly midair to catch insects. Large and powerful shoulder and chest muscles provide power to these thin wings, allowing some species of bats to travel dozens of miles between roosting locations or migrate hundreds of miles seasonally.
Bats have another unique feature, shared by very few animals. Echolocation, or the process in which an animal produces sounds and listens for the echoes reflected from surfaces and objects in the environment. These sounds are produced at a range of 80,000 to 30,000 Hertz by the larynx. As a comparison, a dog whistle has a frequency of 30,000 Hertz. Bats use this specific Hertz range because the average wavelength of the sound is around 4 millimeters (1/8 inch). It is necessary that the wavelengths of the sound be small to be in relation to the dimensions of the objects that the bat is attempting to locate, such as a tiny moth or mosquito, and to be as small as possible to show the fine details of what the sound is being echoed off of. Apart from being required for night time travel, a bat’s call is unique to them. Bat mothers are able to distinguish their babies from millions of other bats because of their distinct voices.
In the light of the COVID-19 pandemic, bats have been starring in news headlines across the globe. It is thought that bats are the original carriers of COVID-19. But the ties between bats and COVID-19 are far more complex than them simply carrying the virus. As mentioned previously, bats have an ancient and disparate history; they have been co-evolving with a broad multitude of viruses as a species for more than 50 million years. Luckily for bats, their evolution of flight has the side effect of making them extremely resistant to viruses. In order to take flight, bats must considerably increase their metabolic rate to create enough energy to power themselves through the air. The process of increasing their metabolic rate creates unsafe molecular byproducts, such as reactive ions, that can harm cells and DNA. While in flight, small pieces of fractured DNA can leave the nuclei of cells through the holes created by the reactive ions and stray throughout the body. To small, brainless cells, stray DNA floating through the bat’s body is indistinguishable from viral attackers. This causes the immune system to kick into overdrive and attempt to secure and destroy the stray DNA by burning it to death, which we know to be the cause of fevers. Of course, stray DNA would continue to be let loose into the bat’s body while they fly and the fever would continue to burn in hopes of killing off the presumed virus. While it is true that viruses cannot survive in extreme heat for a long period of time, it is also true that normal cells also cannot survive in that same heat. In any other animal, this would eventually lead to death as the immune system burns the animal from the inside out. But bats have evolved over millions of years to combat this in the simplest way; their immune system doesn’t react to viral attacks. Because of this, bats have the ability to host many viruses that may have no effect on them but, when introduced to new species, may have dire consequences; as seen in the COVID-19 outbreak. Along with their improved immune system, bats also run into a problem with viruses due to their extremely social lives. Many species live in large communities; congregating in large numbers, huddling together for warmth, grooming one another, and suckling their young. This provides many opportunities for viruses to disperse among the community and find new hosts to carry them.
COVID-19 has had a huge backlash for the already sensitive bat populations around the world. Bats only have three natural predators, owls, hawks, and snakes. But millions of bats die each year due to White-Nose Syndrome, a fungal disease that attacks the bats while they are hibernating and causes them to use their precious fat stores twice as fast as normal and ultimately starves them to death. Whiet-Nose Syndrome is not able to be spread from bat to human but humans often carry spores from the fungus that causes the disease on their clothing or gear into bat territory, causing a deadly outbreak. But more deadly than that is mankind’s destruction of their homes. If humans respected the boundaries of nature, perhaps the bat carrying COVID-19 never would have made contact with humankind. More than half of the bat species in the US are either in rapid decline or are considered endangered. It is a terrifying thought to have that many bat species could go extinct within our lifetime. Without bats we wouldn't have bananas, avocados, or mangoes. Over 300 species of bats help pollinate these fruits so they can grow and reproduce. Bat droppings, called guano, is one of the richest fertilizers in the world. There is nothing about this unique mammal that makes them any less valuable to our world than a human. The story of COVID-19 is a mysterious one that should not be forgotten. We may never know exactly how COVID-19 was spread from a bat to a human, but it is a reminder that the wild should stay wild.
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