What Would Happen If Flies Went Extinct?

In day-to-day life, we think of flies as nothing more than a nuisance, interrupting outdoor meals and invading our homes to distract us with their buzzing. But the importance of flies can't be overstated. Members of the insect order Diptera — known as true flies — comprise more than 150,000 species, including everything from crane flies to fruit flies and even the common housefly. True flies not only pollinate plants, they clean up the world's waste and serve ecological purposes, both as predators and prey. Some true flies can act as decomposers during their larval stages, with the maggots of hoverflies feeding on aphids and helping gardeners in the process. Even house flies have their benefits, which might be surprising considering they also carry some truly terrible diseases, such as anthrax and typhoid fever.

So, while we might think of flies as annoying pests, a world without flies would be one irrevocably changed for the worse. Flies have been around for at least 250 million years and have survived mass extinction events that obliterated other species, including the dinosaurs, so there's not necessarily any cause for concern. But if we were to imagine a hypothetical world in which the insect went extinct, what would that look like? Far from being a pest-free utopia, a fly-free world would actually be a pretty dire — and disgusting — place to live.

Flies may seem like a filthy scourge  — and in many cases they are — but they are also helping to keep the world clean. The insects are composters, acting as nature's recyclers to clean up biological waste by consuming everything from dead wood to rotting flesh and drainpipe slime. Drain flies, for example, consume human waste, and several fly species feed on dead bodies, including those of animals. In the case of the latter, a secondary benefit of this macabre fly behavior is that knowing when certain species lay eggs can help determine the timeline of when a person might have become deceased.

As such, were flies to go extinct, our planet would slowly fill with organic scraps and refuse, and we would live in a world cluttered by biological detritus. Just how bad it would get depends upon certain factors, such as how long it would take for another species that consumes organic matter to take the place of flies. Regardless, the world would become a much filthier and unpleasant place for a long time after flies disappeared, almost certainly causing a sanitation crisis. 

Many ecosystems rely on flies and fly larvae — especially that of the black soldier fly — to break down organic waste and convert it to nutrients necessary for soil fertility. As such, plant growth would suffer significantly without flies. Furthermore, flies are excellent pollinators. In fact, they are the second most important insect that pollinates plants after bees.

A 2019 study published in the Annual Review of Entomology looked at visitors and pollinators of 105 global food crops and found that six families of flies — Syrphidae, Calliphoridae, Muscidae, Sarcophagidae, Tachinidae, and Bombyliidae — visited a wide range of crops. Flies visited an impressive 72 percent of these crops, making them an integral part of the pollination process worldwide. Over in Australia, hoverflies, horseflies, and blowflies pollinate plants such as eucalyptus and tea trees, and flies are also known for being especially useful at pollinating plants in alpine and subarctic environments where bee populations are lower.  If flies went extinct, pollination would take a major hit and global agricultural output would suffer significantly, potentially leading to food shortages. What's more, this would lead to major economic issues, as insect pollination is estimated to be worth around $250 billion worldwide. 

Another major ecological consideration is the fact that parasitic species of flies help reduce the number of crop-eating caterpillars. Certain types of flies, such as Tachinidae, produce larvae that kill numerous pests, reducing the need for chemicals. Were flies to disappear, these pests would proliferate, adding to global agricultural woes. Lastly, flies are also a food source for a wide array of animals such as birds, reptiles, amphibians, spiders, and certain fish, which all form vast, complex, and delicate ecosystems upon which billions of people rely.

Surely one of the most unthinkable consequences of a world without flies would be, well, a world without chocolate. A certain type of biting midge from the family Ceratopogonidae is the only creature that pollinates the flower of the cocoa plant, the beans of which are used to make chocolate.

There are more than 1,000 species in the midge genus Forcipomyia and all of them are tiny, at only 1 to 3 millimeters long. Since the cocoa tree flowers are small and their pollen-producing anthers are hidden inside a hood, this makes the biting midge the ideal pollinator. Cocoa plants have a hard time reproducing anyway; roughly just one in 400-500 cocoa flowers are thought to produce fruit, with only 10% to 30% of pods reaching maturity. Without the flies that pollinate these flowers, the likelihood that cocoa plants would continue to reproduce would be incredibly low.

Chocolate is thought to generate around $98 billion per year, meaning if it were to disappear, the world would be robbed of more than just a delicious treat. Today, the flies that pollinate cocoa plants are native to the areas where cocoa is traditionally grown, such as the Ivory Coast and Ghana. But they also appear in countries where growing cocoa is fairly new, including Brazil, Mexico, Malaysia and Indonesia. Unfortunately, these midges are already facing threats, from climate change and farming expansion to pests and diseases. Therefore, while flies won't disappear tomorrow, the future of chocolate is already in jeopardy.

Flies are incredibly useful in scientific research, as not only are they easy to work with, but they also share the basic DNA of all life, making them crucial to our understanding of modern genetics. They could also provide us with a greater understanding of neuroscience, and even help us heal.

Vivek Jayaraman, a scientist at the Salk institute, spoke to the New York Times in 2017 about his team's work mapping fruit flies' brains "neuron by neuron." The research has identified dozens of new neuron types and neural circuits that flies use to navigate the world, which may provide crucial insights into how other animal brains and our own brains process sensory information and translate it into action.

A more immediately practical example is the use of maggot therapy, which has become increasingly popular in recent years. Maggot therapy involves taking the larvae of the sheep blowfly and green-bottle fly and applying them to patients' diabetic ulcers, bedsores, and other wounds. It might sound archaic, and it certainly is, but the larvae are incredibly effective at eating away infected tissue to clean wounds, and even help to encourage new tissue to grow. Medical professionals have actually found that this cost-effective form of therapy is more effective at cleansing wounds than more conventional dressings, leading to increased usage of this once-prevalent practice across the U.S., Europe, and Australia. Were flies to go extinct, scientific research would be hindered and medical professionals would be robbed of an effective method of cleaning wounds.

Fly extinction might initially sound like a potentially good thing. After all, we tend to think of flies as unsanitary carriers of disease, mainly because they are. Indeed, while the loss of flies from our world would have numerous negative consequences, it would come with some benefits.

Firstly, the extinction of flies would have a major impact on the world economy, but flies themselves are already a problem in that regard. Horn flies, for instance, cause some of the most significant economic damage of all pests when it comes to range cattle in the United States, while the USDA noted back in 2012 that the house fly and stable fly were responsible for damage and control costs of more than a billion dollars per year for United States livestock and poultry production. Flies cause this kind of damage by reducing weight gains in cattle and other livestock, as well as reducing milk production. House flies can also transmit Salmonella in poultry production.

It's not just other animals that flies can affect. The spotted wing drosophila is a major pest for soft fruits in Europe and North America, while fly larvae can directly damage all manner of plants by feeding on root hairs, tender roots, stems, leaf tissue, and fruits. The damage caused by the larvae can allow other fungi to enter the plants, which can prove disastrous. What's more, fully grown flies are able to transmit pathogens between plants. While crops and plant pollination would be severely affected by the loss of flies, then, certain plants would benefit from a lack of the insects.

Perhaps the most obvious benefit of a world without flies would be that the insects wouldn't be able to spread disease. Flies carry all sorts of diseases as a result of contact with rotting organic matter and waste, and can transmit pathogens such as salmonella and E.coli. Still, were flies to disappear, we would be surrounded by organic detritus anyway, so the risk of disease would surely increase without them.