The chances are that if you see a fly land anywhere near a piece of food that you were planning to eat you would swat it away and think nothing else of it.
A new study has found that these annoying winged insects are likely to be carrying far more harmful diseases and illnesses than we previously thought.
Researchers at Pennsylvania State University, Singapore's Nanyang Technological University and the Federal University of Rio de Janeiro studied microbiomes of 116 house and blowflies from around the world.
They found that the average fly is often carrying hundreds of different types of bacteria on its legs and wings, which they have picked up from faeces or carcasses and are easily transferred to the surfaces they land on.
The study describes flies as "airborne shuttles" for bacteria and that they are the perfect vehicle for bacteria to spread its nastiness around.
The legs and wings show the highest microbial diversity in the fly body, suggesting that bacteria use the flies as airborne shuttles.
It may be that bacteria survive their journey, growing and spreading on a new surface.
Therefore if you are eating something that a fly has landed on you are more than likely to be consuming some bad bacteria.
One of the bacteria that they were found to carry was Helicobacter pylori, which can often cause nasty ulcers to form in your gut.
There is some good news if you live in the country as city-dwelling flies were found to carry more germs than those in the countryside.
Professor Donald Bryant, of Penn State, adds:
[The study] will really make you think twice about eating that potato salad that’s been sitting out at your next picnic.
We believe that this may show a mechanism for pathogen transmission that has been overlooked by public health officials, and flies may contribute to the rapid transmission of pathogens in outbreak situations.