Do flies really throw up on my food when they land on it? – Henry E., age 10, Somerville, Massachusetts
Imagine you’re at a picnic and just about to bite into your sandwich. Suddenly you spot a fly headed your way, homing in on your food with help from its compound eyes and antennae. It manages to escape your swatting, lands on the sandwich and then seems to throw up on it!
It can look kind of gross, but the fly might be just airing out its own digested food, or spitting on yours.
Most of the over 110,000 known fly species have no teeth, so they cannot chew solid food. Their mouthparts are like a spongy straw. Once they land on your food, they need to release digestive juices to liquefy it into a predigested, slurpable soup they can swallow. In short, some flies are on a liquid diet.
To fit more food in their stomachs, some flies try to reduce the liquid in what they have already eaten. They regurgitate food into vomit bubbles to dry it out a bit. Once some water has evaporated they can ingest this more concentrated food.
Human beings don’t need to do all this spitting and regurgitating to get nutrients out of our food. But you do produce a digestive juice in your saliva, an enzyme called amylase, which predigests some of the sandwich bread while you chew. Amylase breaks down starch, which you can’t taste, into simple sugars like glucose, which you can taste. That’s why bread gets sweeter the longer you chew it.
Did you know flies can taste food without their mouths? As soon as they land, they use receptors on their feet to decide whether they’re on something nutritious. You may have noticed a fly rubbing its legs together, like a hungry customer getting ready to devour a meal. This is called grooming – the fly is essentially cleaning itself, and may also clean the taste sensors on the bristles and fine hair of its feet, to get a better idea of what is in the food it has landed on.
Should you trash food a fly’s landed on?
When a fly touches down on your sandwich, that’s probably not the only thing it’s landed on that day. Flies often sit on gross stuff, like a dumpster or decomposing food, that’s full of microbes. The germs can hitch a ride and, if the fly stays put long enough, hop onto your meal. This is much more dangerous than their saliva because some of the microbes can cause diseases, like cholera and typhoid. But if the fly doesn’t stay longer than a few seconds the chances of microbes transferring are low, and your food is probably fine.
To keep insects from landing on your food, you should always cover it. If your house is infested with flies, you can use simple traps to get rid of them. Carnivorous plants can also eat the flies and help control their population.
Are flies good for anything?
Spitting on food and spreading diseases sounds disgusting, but flies aren’t all bad.
Watch closely the next time you’re outside and you might be surprised by how many flies visit flowers to get nectar. They’re an important group of pollinators, and many plants need flies to help them reproduce.
Flies are also a good source of food for frogs, lizards, spiders and birds, so they’re a valuable part of the ecosystem.
Some flies have medical uses, too. For example, doctors use blow fly maggots – the young, immature form of flies – to remove decomposing tissue in wounds. The maggots release antiviral and antimicrobial juices, and these have helped scientists create new treatments for infections.
So, although it’s a nuisance to shoo flies away from your sandwich, maybe you can spare a few bits of your lunch?
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Jamie Theobald receives funding from the National Science Foundation: IOS-1750833.
Ravindra Palavalli-Nettimi does not work for, consult, own shares in or receive funding from any company or organisation that would benefit from this article, and has disclosed no relevant affiliations beyond their academic appointment.
This article is republished from The Conversation under a Creative Commons license.
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Much of the plant life, including flowering plants and human food crops, require pollination. Without pollinators, these plants would never reproduce.
Pollinators come in all shapes, sizes, colors, and species. There are birds, bees, beetles, flies, moths, bats, and even a tiny flightless mammal—the honey possum—that specialize only on specific plants as their preferred food source. Other pollinators include the sun bear and the Noronha skink, and research suggests that some pollinators, like certain butterflies and birds, have even evolved with the specific plants they pollinate.
Honeybees and bumblebees have long been instrumental in pollinating human foods, including fruits, nuts, vegetables, and many staple crops, and research reveals that about one in three bites of food humans eat requires pollinators.
Stacker scoured national and international government data, educational resources, science journals, and news reports to bring readers 20 interesting facts about pollination. From honeybees to honey possums, pollinators are part of a fundamental process of life on Earth, sometimes known as an "ecosystem service."
Stacker's slideshow includes information from recent studies revealing widespread declines in key pollinator populations around the world. Research shows that without pollination and pollinators, humans and many other species would not survive, and scientists from the United Nations say that human impacts have led to current extinction rates, which are 100 to 1,000 times higher than normal.
Many institutions and governments are recognizing the importance of reversing the decline in the number of pollinators and are actively figuring out ways to help restore the pollinator population. Factors like agriculture, pollution, climate change, urban development, and change in land use are putting pollinator species at risk.
Click through the slideshow to discover the essential roles pollinators play in sustaining life on Earth and what's being done to save them.
Pollinators are building blocks in the foundation for life on Earth. Without pollinators, over 80% of the world's flowering plants would fail to reproduce. Humans and many other species evolved to eat food that only exists because of pollinators. Many other plants, including those of staple food crops for people, exist only because of their pollinators.
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Like a dance with two partners, the plant and the pollinator are essential for the dance to work. Pollinators of all kinds have each evolved to "dance with" a particular partner, their plant companion. Each pollinator visits their plant as they look for food, mates, shelter, and nest-building materials. Meanwhile, the plant is "pollinated" or fertilized when the pollinator moves fertile grains of pollen from one plant to the next, and it reproduces. Without both partners in this dance, in many cases, neither reproduces.
As the U.S. Forest Service says, "The secret bond of the partnership is that neither plant nor pollinator populations can exist in isolation—should one disappear, the other is one generation away from disaster."
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You're probably familiar with bees, butterflies, and birds visiting flowers and pollinating them. Maybe you've seen bees busy pollinating flowers in a garden or meadow. Besides bees, pollinators include ants, bats, flies, mammals, moths, wasps, and many other animals.
Out of all the pollinators on Earth, honeybees (Apis mellifera) may be the most vital to human food production. Most domesticated food staple crops, including fruit, and vegetables, are pollinated by honeybees. The bees, in turn, have been introduced around the world along with the crops they help pollinate. Honeybees are also important in producing wax, honey, and royal jelly.
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A 2016 study from Penn State shows that both pollution and climate change affect honeybees. Pollutants can impact bees' scent tracking abilities by affecting their ability to find and pollinate their food. Meanwhile, other research shows that the increases in dry weather and temperature can stress bees and change their behavior as well, suggesting that climate change is a threat to beekeeping and pollination.
2020 research from the journal Science shows that bumblebees—also key pollinators for human food—are down a whopping 30% in North America and Europe. The study suggests that bumblebees can't tolerate increases in temperature and the frequency of climate extremes. The scientists saw significant drops in populations in recent decades, and the senior author of the study said, "The things [we] grew up with as kids are fading away very fast."
Besides pollution and climate change, other challenges for honeybees include several diseases. One of these is called American foulbrood, a bacterial disease killing many honeybee colonies. Other threats to honeybees, bumblebees, and many other pollinators, include land-use changes, habitat loss, invasive species, climate change, and pollution. According to the Food and Agriculture Organization of the United Nations, "present species extinction rates are 100 to 1,000 times higher than normal due to human impacts. Insects will likely make up the bulk of future biodiversity loss with 40% of invertebrate pollinator species—particularly bees and butterflies—facing extinction."
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Many species depend on pollinators to fertilize plants they rely on for food and so much else. Organizations and researchers are actively working to restore, support, and bring resilience to pollinator populations of all kinds.
For example, science-based conservation and management organizations have shown that wetlands are essential ecosystems not only for ducks but also many wild pollinators. And some areas around the world serve as pollinator "hotspots" in need of special protections.
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Once an iconic and common species, western monarch butterfly populations are almost completely gone from their former habitat throughout western North America, according to the journal Frontiers in Ecology and Evolution. The authors write, "The population may now be hovering at its quasi-extinction threshold." However, many are working to restore milkweed populations—the partner plant that monarchs pollinate and rely on for food.
Many other pollinator species face extinction, and like honeybees and bumblebees, the monarch butterfly is a prominent and once common species that many people in the United States recognize.
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Ants are among the most diverse, abundant, and ecologically important insects on Earth. Some ant species are also pollinators, and they eat nectar from flowers. However, ants crawl into the flowers they feed on and may or may not end up with pollen on their bodies, so many ants are not effective at moving pollen from one flower to another, which is necessary for pollination.
Bats across the world are vital pollinators of many flowering plants. Especially in the desert and tropical regions, bats that feed on flower nectar are essential in pollination and reproduction. Over 300 kinds of fruits depend on bats for pollination, including mangos, bananas, and guavas. Flowers that attract bats are typically large and open at night. The lesser long-nosed bat and the Mexican long-tongued bat both migrate over a thousand miles and are listed as endangered species.
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Most bear species are omnivores, meaning they feed on a variety of berries, fruits, plants, fish, other animals, and honey. Many of these plants require pollinators. These foods include berries, fruits, and nuts. Interestingly, the sun bears of Asia have evolved specialized long tongues that allow them to access tree cavities where they find honey and insect pollinators.
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Endemic to Australia, honey possums are tiny mammals with extremely long tongues that have evolved to eat only the nectar and pollen of flowering plants, including banksias, eucalypts, and heath. Their aboriginal name is Noolbenger. They have also evolved a prehensile tail that curls around their plants and flowers as they hold on to eat.
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At least 2,000 bird species worldwide are pollinators. These birds—in a wildly colorful and diverse assortment of partnerships—feed on the nectar, insects, and spiders associated with their preferred flowers. In the U.S., hummingbirds are especially important to wildflowers, while honeycreepers and honeyeaters are vital to wildflowers in Hawaii and Australia, respectively.
Besides monarch butterflies, many other species of butterflies and moths are at risk from pollution, human development, climate change, agriculture, and sweeping changes in land use. Butterflies and moths are like jeweled pollinators, and many seemed to have evolved to look like the flowers they pollinate. However, other species are cryptic and drab, depending on their environment and predators. Research suggests that monarchs are so vivid because the milkweed they feed on makes them taste bad to predators.
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Many beetle species are pollinators. As one of the oldest groups of insects on Earth, they are among the world's first insect pollinators. Like flowers that evolved with their particular bats, birds, butterflies, and moths, flowers pollinated by beetles have special features. These flowers typically are bowl-shaped, have fruity nectar, and bloom during the day. Two of the most ancient flowering plants pollinated by beetles are magnolias and spice bushes.
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Scientists meet annually to share research on the health and biology of the world's pollinators. The International Pollinator Conference includes hundreds of scientists from around the world who bring updates on ecology, genes, and managing bees and other pollinators, land use and management, and helping pollinator populations globally.
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The pollinators on Earth are much greater than the sum of their parts. It is now commonly understood in science that Earth's pollinators perform what people now call "ecosystem services"—functions and tasks in nature so essential to life on Earth that humans and many other species would not be able to survive without them.
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Pollinators are also now widely understood to be in peril, and many governments, organizations, and institutions are working to recover, regenerate, and restore the Earth's pollinator population. Many pollinator "hotspots," places people are creating or restoring in cities, gardens, and natural zones around the world, are becoming increasingly important to the conservation process. In a 2019 article in Nature Ecology and Evolution, scientists write, "Urban areas are often perceived to have lower biodiversity than the wider countryside, but a few small-scale studies suggest that some urban land uses can support substantial pollinator populations."