It feels like a yeti sighting or the appearance of a swamp creature, something you hear about a lot on the internet but not really actually sighted. You’ll see blog posts and reports of this folksy method for repelling flies–restaurants and shops festooned with ziploc bags filled with water that dangle from, well, whatever they can be attached to.
But these are not decorations. They have a purpose to those who hang them. The theory goes like this: flies have 3,000 to 6,000 simple eyes that make up their entire complex eye. These simple eyes neither move nor focus, but they do provide individual pieces of an image similar to the way each pixel on a screen provides a piece of an image. Now to the bags: water refracts light (which means it is bent from its normal straight path). This refraction, according to bag believers, confuses the simple fly eyes and causes them to move to other areas. Some proponents of the theory say that the bags must contain coins or pieces of tin to make the effect work.
So does it? Certainly the explanation sounds sciency enough. Maybe not so much! If you prefer popular science, a 2010 airing of Myth Busters tested the theory by releasing flies in a chamber where they had the option of choosing either a path with just rotten meat at the end or a path with rotten meat and a water-filled bag at the end. More flies by far chose the water-bag path. If you opt for hard science, a study by Mike Stringham, professor of entomology at North Carolina State University, placed water filled repellents on two egg farms and measured regurgitated substances that flies leave after feeding in both bagged and non-bagged areas. Results showed higher fly activity in the bagged areas.
So what can you do to repel pesky flies? Most experts agree on the basics: wipe up spills immediately, put away exposed food items as soon after use as possible, empty your trash regularly and keep garbage can lids closed tight, and use screens on doors and windows to prevent flies from entering in the first place. Other methods that may work include placing fans in the areas where you are (works better for fruit flies); using scents that flies supposedly avoid, such as citronella, cedar, cinnamon, citrus, rosemary, and basil; placing marigolds to ward off flies; or even using fly traps of water or vinegar in a bowl with a few drops of dish soap in them (also works best with fruit flies).
Still want to give the bag theory a try. Why not? Just don’t confuse correlation with causality. You can buy a witch ball in Salem and place it in your yard and you probably won’t see witches but there are other factors at play, such as how many witches you were seeing before or, well, whether witches exist or not. Flies, of course, do exist, but their lack of presence in an area where a water bag is hanging doesn’t necessarily mean that the device is the cause.
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Written by Ivan Young in partnership with IMS Bolt maintenance supplies and equipment.
