Buzz
Do the water bags in this restaurant truly safeguard diners? Matt Murphy/Flickr (CC by 2.0)If you’ve ever dined out and noticed transparent bags filled with water dangling near entrances or outdoor seating, you might wonder, 'What’s the purpose? Is this some innovative temperature hack or a cost-saving trick for water storage?'
Although any impact on temperature is unintentional, these suspended bags are primarily used to deter pests. Many hang them outside homes, businesses, and barns to keep flies at bay.
There are numerous interpretations of the water-bag technique. Some proponents claim that adding floating tin foil flakes is essential, while others recommend tossing in a couple of pennies. A few enterprising websites have even commercialized the idea, offering specially crafted water bags marketed as pest repellents.
Given that flies frequently hover around germ-infested areas like trash bins, animal remains, and waste, it’s no surprise they’re unwelcome guests. Laden with bacteria, they often land on your food, making it understandable why you’d want to shoo them away. Beyond being a nuisance, flies are also carriers of diseases.
But how does a simple water bag deter flies? Is it even effective? Opinions are divided among experts and enthusiasts alike. Let’s explore both perspectives on this intriguing topic.
Why Flies and Water Bags Just Can't Get Along
The water bag approach to
How does this method repel flies? Some argue that flies mistake the clear liquid for a body of water. Others believe the insects flee upon seeing their magnified reflection. However, the most widely accepted explanation among entomologists and inventors is straightforward: light refraction.
Refraction occurs when a transparent or semi-transparent object, like a glass or water-filled bag, changes the direction and speed of light. Normally traveling in straight lines, light rays bend, creating optical illusions such as mirages that can also perplex humans. For a deeper dive into refraction, check out How Light Works.
In theory, refraction can disorient certain insects, particularly the housefly. This insect possesses a highly sophisticated set of eyes, enabling it to see in multiple directions simultaneously.
The housefly’s head is dominated by two large, intricate eyes, each made up of 3,000 to 6,000 simple eyes. Unlike human eyes, these cannot move or focus, but they offer the fly a mosaic-like view of its surroundings. Each simple eye contributes a small piece of the visual puzzle, similar to how a pixel adds detail to an image on a screen.
The Anatomy of a Housefly's Head
MytourHouseflies determine their direction based on the angle of sunlight. Entomologists propose that when their intricate, sensitive eyes encounter refracted light, the insects become disoriented and flee.
While some enthusiasts assert that water bags repel all flying insects, most success stories involve species with complex eyes, such as houseflies.
There’s little clarity on the specifics, such as the required water volume, the number of bags needed, or the optimal placement for maximum effectiveness.
Skeptical? You’re not the only one. Let’s explore some of the criticisms surrounding this optical fly deterrent.
Debunking the Water Bag Myth
What would stop a housefly from landing on this delicious piece of meat if a water bag is supposed to deter it? Robert Recker/Corbis/Getty ImagesMany skeptics doubt the effectiveness of water bags in repelling flies. The MythBusters team, for instance, labeled this claim as debunked. Critics often dismiss the theory as folklore or superstition, attributing any perceived success to a mix-up between correlation and causation.
Picture this: A salesman offers you a deal too good to pass up—a $19.95 belt buckle that supposedly wards off shark attacks. You wear it for a week, and lo and behold, no shark bites occur. Does this prove the buckle’s effectiveness? Is there a genuine link between wearing it and avoiding sharks? To truly assess this, you’d need to consider how often sharks approached you before and the myriad other factors that might explain their absence.
If all variables aren’t considered, hanging water bags to repel flies might appear effective due to the placebo effect. In medical contexts, this happens when individuals feel better after receiving a treatment, even if it’s ineffective. Similarly, people might believe they’re solving a pest problem, even if the solution does nothing.
But what if the situation worsens? What if the placebo actually aggravates the issue? Mike Stringham, an entomology professor at North Carolina State University, explored the use of clear plastic water bags as a fly deterrent and found this to be the case.
Stringham conducted a 13-week field study by installing commercial water-based optical fly repellents on two egg farms. He measured fly activity by tracking the regurgitation spots left by feeding flies. His findings revealed that areas with water bags had higher housefly activity.
However, the study wasn’t conducted under natural lighting. Its goal was to assess whether water bags could reduce fly populations on egg farms. It didn’t investigate whether direct sunlight enhanced the bags’ effectiveness.
So, do water bags reduce housefly numbers around homes and restaurants? Some theories suggest yes, but substantial evidence points to no. Despite this, water bags continue to hang near restaurant patios and backyard porches worldwide.
