The war over flies and our food has been raging for centuries. For as long as there have been picnics, open windows or any unwanted interaction with nature, people have been trying to prevent nature from ruining their lunch. Often, this has been completely unsuccessful.
Probably because we’re used to seeing them clustered around piles of dog poo or the rotting remains of recently deceased animals, people are often incredibly paranoid about the prospect of their food being assaulted by a fly. Unlike most weird fears, this one definitely has some logic. But, given how many times our food gets accosted by winged creepy crawlies, does it make sense that we should still want to throw everything away the minute it gets touched by something with more than two legs? As ever, the truth is more complicated than it might seem.
Unfortunately for germaphobes, the science behind what actually happens when a fly lands on your food is more horrific than you could possibly imagine. Rather than having a little rest on the corner of your sandwich, what the fly is actually doing is enough to keep you up at night.
Whenever a fly lands on a new surface, it immediately begins the hunt for food. If it decides that what it has found could be delicious, it then starts what is one of the most unappetising eating methods of any animal on earth. Since flies can’t chew, they need to find a way to liquidise their lunch before they begin to digest it. To do this, they vomit up a complex mixture of enzymes and saliva that helps to break down the food, before they slurp it back up. If you ever spot a fly looking suspiciously still in the middle of a salad bowl, there’s a good chance that this is what they’re doing. Coupled with the likelihood that they’ve just flown in from a yummy pile of dog poo, you could be forgiven for never wanting to eat anything ever again.
The risks posed by pathogen carrying flies are significantly increased depending on where you are in the world. In many developing economies, health workers are constantly coming across cases where people have contracted infectious diseases such as cholera and typhoid from coming into contact with a piece of contaminated food. For many, spotting a fly on your dinner carries a far greater risk than just being a little off-putting.
However, despite the dangers, the reality is that the risks associated with eating food touched by a fly are comparatively low. According to food hygiene expert Dr Cameron Webb, any germs transferred by an errant fly are extremely unlikely to make you ill. According to Dr Webb, a fly’s size means that a single touch down is unlikely to have an impact large enough to effect the average healthy person, who’s immune system would most likely be able to repel any nasty bugs.
In addition, Dr Webb also suggests that where you live could play a vital role in determining how concerned you should be. According to his research, flies that live in urban areas are, somewhat surprisingly, considered to be less harmful than those in the countryside, as the presence of insecticides and other chemicals tends to keep their numbers in check. So much for all that fresh air being the answer to a healthy lifestyle.
Though there is little doubt that flies can carry everything from infectious disease to nasty parasites, the average person has little to fear from contaminated food. Because they have spread to almost every corner of the globe, it’s next to impossible that we haven’t eaten something that’s been vomited on at least once. As with anything it’s a case of common sense. A quick landing is nothing to worry about. A swarm of wriggling bodies and you might want to reconsider what you have for dinner.