“This video is made from a microscope when the fly sits on our food then what does it do?” the caption reads. “Send it to everyone so that everyone know why its important to cover our food!!”
First posted in July 2018, the video has been shared more than 700,000 times.
But do flies always lay maggots – their young, also known as larvae – on food?
Flies don’t give birth or lay eggs on food
Dr Pia Addison, from the integrated pest management unit at Stellenbosch University’s Department of Conservation Ecology and Entomology in South Africa, told Africa Check the fly in the video was a “flesh fly”, one of thousands of similar species in the Sarcophagidae family of flies.
The female flesh fly, she said, was “known to give birth to live young, a process known as viviparity, whereby initiation of egg development takes place within the mother, which thus gives birth to live larvae”.
The fly in the video “was just ready to birth her young at that point”, Addison said. It didn’t release the maggots because it was sitting on food – and the video doesn’t show it on food. (Note: You can check out other videos showing this.)
Dangers of flies on food?
Flies – and there are more than 120,000 species of them on the planet – don’t have teeth, so they can’t chew their food.
Instead, a fly spits an enzyme onto something it wants to eat. This dissolves the food. The fly then sucks the food up through its long sucking mouthpart.
Some people think this means flies vomit on food – maybe even on our food. They don’t.
“Most flesh flies feed on decaying material, often of animal origin, and are therefore key decomposers in our ecosystem,” Addison told us. But they also eat poo. “I wouldn’t want them to land on my food!”
‘Very little threat’ of flies on food
In the January 2017 article Flourishing in Filth: House Fly–Microbe Interactions Across Life History, Dana Nayduch of the US Department of Agriculture explains the risk when flies land on your food.
“Every day you touch doorknobs, money, and credit cards, and then you bite your nails or rub your eye and inoculate yourself with bacteria, but our immune system takes care of it,” she writes.
“So flies pose very little threat.” – Eileen Jahn and Taryn Willows
For publishers: what to do if your post is rated false
A fact-checker has rated your Facebook or Instagram post as “false”. What should you do? First, don't delete!
Click on our guide for the steps you should follow.
Africa Check teams up with Facebook
Africa Check is a partner in Facebook’s third-party fact-checking programme to help stop the spread of false information on social media.
The content we rate as “false” will be downgraded on Facebook and Instagram. This means fewer people will see it.
You can also help identify false information on Facebook. This guide explains how.