They are one of the scourges of summer and have been ruining picnics since the dawn of time (probably).

Flies – harmless but incredibly annoying, most people think.

But it turns out the insects may be a lot more dangerous than we thought.

The average fly carries 200 different types of harmful bacteria, largely thanks to the various things they land on, such as rotting food and fecal matter. Even if you swat one away as soon as it’s landed on your sandwich, the damage has already been done.

Thanks to thousands of tiny hairs on their arms and legs, the bacteria are quickly transferred to your food, which could pose serious health risks according to a pest control expert.

“They only need to touch your food for a second for their legs or the tiny hairs all over their bodies to transfer germs from all those nasty things they eat onto what you are eating,” Ron Harrison, an entomologist and technical services director at Orkin pest control, told the Mail Online.

“And since flies can transfer serious, contagious diseases like cholera, dysentery, and typhoid, it is probably best if you avoid eating things that a fly lands on.” What’s more, flies nearly always vomit on any food upon which they land.