It only takes a single fly to alight on your picnic lunch to make you uneasy about what germs may have landed with it. But what harm can come from a fly landing on your food? Should you throw it away?
There are hundreds of different fly species in Australia. This diverse group of insects ranges from mosquitoes and biting midges to bush flies and blowflies.
Many of these flies pose a health risk but none hang about our homes more than the house fly. It’s a ubiquitous presence during the warmer months, can be a substantial annoyance and may also be a potential health risk.
Musca domestica, commonly known as the house fly, is one of the most widespread nuisance insects in the world. It has found a place in and around our homes. It is closely associated with rotting organic waste, including dead animals and faeces. It’s no surprise they’re commonly known as “filth flies”.
After laying eggs, maggots will hatch out and eat their way through the decaying organic material before pupating and then emerging as an adult fly a few days later. The adult flies can live up to a month and may lay hundreds of eggs over that time.
From poop to plate
When it comes to passing on pathogens, it’s not necessarily the fly itself but where it’s come from that matters. Flies don’t just visit freshly made sandwiches. They spend far more of their time in rotting animal and plant waste. Among this waste can be a range of pathogens and parasites.
House flies don’t bite. Unlike mosquitoes that transmit pathogens of human health importance in their saliva, 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.
Flies don’t have teeth. They can’t take a bite out of our food, so they have to spit out some enzyme-rich saliva that dissolves the food, allowing them to suck up the resulting soup of regurgitated digestive fluids and partially dissolved food. 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.
Brush off or toss out?
In most instances, spotting a fly on your food doesn’t mean you need to throw it out. While there is little doubt that flies can carry bacteria, viruses and parasites from waste to our food, a single touchdown is unlikely to trigger a chain reaction leading to illness for the average healthy person.