What Happens When a Fly Lands on Your Food?

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"Waiter, what's this fly doing in my soup?"
"Transmitting bacteria, sir."

This gross response doesn't make a great punchline (nor will it earn anybody a big tip), but it is the truth. But why is that fly just sitting—or swimming—there? And is the soup still safe to eat? If you really want to know, gird yourself and read on.

The common house fly (Musca domestica) has no venom, no stinger, and no fangs. It finds its food in a peaceful way—by rolling around in other animals' waste and garbage. With no teeth, the fly requires a liquid diet. This would be a problem, since a lot of food is solid, but the fly has a disgusting workaround: It spits and pukes on its meal. Compounds in its saliva and bile break down the food, making it as slurpable as a smoothie.

As the fly eats, it's usually also pooping—and if it's female, possibly laying eggs as well. Flies really are an absolute bonanza of disgustingness.

All of this would be gross, but ultimately harmless, if flies only ate soup. But they're opportunists. They eat rotting garbage and they eat animal feces, and in doing so they consume loads of pathogens.

"House flies are the movers of any disgusting pathogenic microorganism you can think of," Jeff Scott, an entomologist at Cornell University, told the Daily Mail. "Anything that comes out of an animal, such as bacteria and viruses, house flies can take from that waste and deposit on your sandwich."

Experts estimate that adult houseflies can transmit more than 100 different diseases and parasites, from Salmonella and tuberculosis to tapeworms.

Does this mean we should immediately throw out any food a fly has touched? Probably.

According to research initiated at Penn State Eberly College of Science and in collaboration with the Nanyang Technological University in Singapore and other international institutions , houseflies tend to harbor pathogens on their legs, meaning even a brief touchdown on your tuna melt could very conceivably transmit any number of worrisome bacteria in an instant. It's better to keep picnic foods sealed until they're needed or to ask for a new dish if your local restaurant has any unsolicited, winged guests lurking around. 

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What is a Polar Vortex?

Edward Stojakovic, Flickr // CC BY 2.0
Edward Stojakovic, Flickr // CC BY 2.0

If you’ve turned on the news or stepped outside lately, you're familiar with the record-breaking cold that is blanketing a lot of North America. According to The Washington Post, a mass of bone-chilling air over Canada—a polar vortex—split into three parts at the beginning of 2019, and one is making its way to the eastern U.S. Polar vortexes can push frigid air straight from the arctic tundra into more temperate regions. But just what is this weather phenomenon?

How does a polar vortex form?

Polar vortexes are basically arctic hurricanes or cyclones. NASA defines them as “a whirling and persistent large area of low pressure, found typically over both North and South poles.” A winter phenomenon, vortexes develop as the sun sets over the pole and temperatures cool, and occur in the middle and upper troposphere and the stratosphere (roughly, between six and 31 miles above the Earth’s surface).

Where will a polar vortex hit?

In the Northern Hemisphere, the vortexes move in a counterclockwise direction. Typically, they dip down over Canada, but according to NBC News, polar vortexes can move into the contiguous U.S. due to warm weather over Greenland or Alaska—which forces denser cold air south—or other weather patterns.

Polar vortexes aren't rare—in fact, arctic winds do sometimes dip down into the eastern U.S.—but sometimes the sheer size of the area affected is much greater than normal.

How cold is a polar vortex?

So cold that frozen sharks have been known to wash up on Cape Cod beaches. So cold that animal keepers at the Calgary Zoo in Alberta, Canada once decided to bring its group of king penguins indoors for warmth (the species lives on islands north of Antarctica and the birds aren't used to extreme cold.) Even parts of Alabama and other regions in the Deep South have seen single-digit temperatures and wind chills below zero.

But thankfully, this type of arctic freeze doesn't stick around forever: Temperatures will gradually warm up.

In What Field Was Dr. Martin Luther King, Jr. a Doctor?

Express Newspapers/Getty Images
Express Newspapers/Getty Images

Martin Luther King, Jr. earned a doctorate in systematic theology from Boston University in 1955. He’d previously earned a Bachelor of Arts from Morehouse College and a Bachelor of Divinity from Crozer Theological Seminary. His dissertation, “A Comparison of the Conception of God in the Thinking of Paul Tillich and Henry Nelson Wieman,” examined the two religious philosophers’ views of God in comparison to each other, and to King’s own concept of a "knowable and personal" God.

Some three decades after he earned his doctorate, in 1989, archivists working with The Martin Luther King Papers Project discovered that King’s dissertation suffered from what they called a “problematic use of sources.” King, they learned, had taken a large amount of material verbatim from other scholars and sources and used it in his work without full or proper attribution, and sometimes no attribution at all.

In 1991, a Boston University investigatory committee concluded that King had indeed plagiarized parts of his dissertation, but found that it was “impractical to reach, on the available evidence, any conclusions about Dr. King's reasons for failing to attribute some, but not all, of his sources.” That is, it could have been anything from malicious intent to simple forgetfulness—no one can determine for sure today. They did not recommend a posthumous revocation of his degree, but instead suggested that a letter be attached to the dissertation in the university library noting the passages lacked quotations and citations.

Have you got a Big Question you'd like us to answer? If so, let us know by emailing us at bigquestions@mentalfloss.com.

This article was originally published in 2013.

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