Science: Food should be a no fly zone

Flies are less apparent in the winter months but when they make an appearance around your food or drinks, the annoyance and disgust that follows never fails. But, exactly how dangerous are they? Once a fly lands on your sandwich or pop can should you consider it contaminated and throw in out?

One article discusses this occurrence that explains that there are hundreds of different fly species — all that play an important role in the environment by assisting decomposition, pollinating plants and providing food for insectivorous predators.

Many of these flies pose a health risk but none hang about our homes more than Musca domestica, also known as the house fly. Over time, this fly has been closely associated with rotting organic waste, including dead animals and feces, so it’s no surprise they’re commonly known as “filth flies.”

The article states that 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.

When it comes to the passing of pathogens, however, it’s not necessarily the fly itself but where it’s comes from that matters. Flies spend much of their time in rotting animal and plant waste, which can hold a range of pathogens and parasites.

This means when they land on your picnic spread, they can leave behind pathogen-filled footprints, and that’s not all. Because they don’t have any teeth, they can’t take a bite out of food. Instead, 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.

However, 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, a single touchdown is unlikely to trigger a chain reaction leading to illness for the average healthy person. Flies that land out of sight and wander about for a few minutes vomiting and pooping on your food or food preparation area are more of a concern. The more time passes, the greater the chance of pathogens left behind by the flies growing and multiplying on our food. That’s when health risks increase, the article explains.

Having plenty of flies about can be a concern and risk is generally higher in regions away from large cities. There are not only likely to be higher numbers of flies but a greater chance they’ll be in contact with dead animals and animal waste. There is no shortage of opportunities for flies in the city either but, for the most part, insecticides and improved hygiene standards assist in fly control and minimizing the risk of contact with contaminated substances.

To control flies on your food or around during food preparation, ensure your food is covered while preparing, cooking and serving outdoors and don’t leave leftovers sitting around outside for flies. Screening windows and doors will help block flies from coming inside as well, and also minimizing garbage around the house is critical. Ensure bins are cleaned regularly, household garbage is covered and animal waste is routinely cleaned up. The addition of insecticidal surface sprays around bin areas will help and, inside the home, a range other disinfectant sprays will keep the numbers of flies down.

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