Video explaining how flies eat our food goes viral, prompting widespread disgust - and a lot of questions

A house fly on a doughnut (stock image) with inset vomiting emoji
Photo credit: Getty Images

Have you ever wondered what flies do when they land on your food? Well, we have the answers - but we kind of wish we didn't.   

A video by the popular YouTuber Zack D. Films - who has grown a substantial following for his informative content spanning a wide variety of topics - has recently gone viral for explaining how the insects actually consume our food.

Zack, who has more than 7.14 million subscribers on YouTube and 1.1 million on Instagram, shared the video earlier this week to widespread revulsion, with many taking to the comments to express their disgust.

Alongside an animated video of a fly landing on a hamburger, Zack explained that flies, unlike humans, cannot chew as they don't have teeth.

"Instead, they sort of puke up a special type of saliva right onto your meal," Zack narrated the animation. "This saliva contains digestive enzymes that break down your food into a slurpable liquid.

"The fly then uses its proboscis [an elongated sucking mouthpart] to suck it up like a smoothie, which is how they consume your food."

Viewers didn't take too kindly to the creepy-crawly revelation, with one clearly panicked individual exclaiming in the comments: "How fast does this happen? Like if they land lightly and I'm quickly like NOOOOOO! It hasn't happened yet. Right? RIGHT???"

"Life was good before knowing this fact," said another, a comment that has since racked up more than 323,400 likes alone.   

"I miss the person I was 2 minutes ago," another joked, while a fourth added: "I could have [gone] my entire life not knowing this." 

At the time of writing, the video has amassed over 1.665 million likes and 30,800 comments.

House fly feeding on a sugary snack - stock photo
"Life was good before knowing this fact." Photo credit: Getty Images

And if you're questioning Zack's research, unfortunately, he's right. In an article for The Conversation in 2015, Dr Cameron Webb, a clinical lecturer at Sydney Medical School, noted as flies don't have teeth, they instead "spit out enzyme-rich saliva that dissolves the food, allowing them to suck up the resulting soup of regurgitated digestive fluids and partially dissolved food."

Should I throw my food out if a fly lands on it?   

In most cases, spotting a fly on your food doesn't mean it needs to be tossed, Dr Webb explained, noting a single touchdown is "unlikely" to trigger illness for the average healthy person.   

However, flies that land out of sight and "wander about for a few minutes vomiting and pooping on your food or food preparation area" are more of a concern, he said.

"The more time passes, the greater the chance of pathogens left behind by the flies growing and multiplying on our food. That’s when health risks increase."   

As flies are very common in New Zealand, especially during the summer, it's normal for most of us to accept their presence and not think too much about it. But Dr Webb warned flies can carry pathogens and parasites, which they pick up on their feet and body from landing on rotting organic waste, faecal matter and yes, dead animals.

"When it comes to passing on pathogens, it’s not necessarily the fly itself but where it’s come from that matters," he said.

"House flies transmit pathogens on their feet and body. As well as leaving behind pathogen-filled footprints, the flies leave their poop on our food. They vomit too.    

"If a fly has plenty of time to walk around on our food vomiting up, sucking in and defecating out, the chances of leaving behind a healthy population of pathogens are high."   

To help prevent these greedy houseguests from making frequent visits, Dr Webb highlighted the importance of covering your food while cooking, preparing and serving, as well as keeping the house clean, minimising and covering household rubbish and ensuring bins are cleaned regularly. Insecticidal surface sprays around bins can also help, as well as fly sprays - and of course, a good old-fashion fly swat can work a treat.