Flies are a common sight, often drawn to our food. Understanding why they land on our food and the potential health implications is important. This exploration delves into the biological mechanisms that drive flies towards our food and the processes that unfold once they land.
The Allure of Food
Flies possess highly developed sensory systems that enable them to efficiently locate potential food sources. Their primary method for detecting food is through their acute sense of smell, known as olfaction. Flies use specialized receptors on their antennae to detect chemical cues released by various substances, including sugars, proteins, and decaying organic matter. This allows them to identify suitable meals from a considerable distance, sometimes even miles away.
Beyond their sense of smell, flies also rely on compound eyes for visual detection of visible food sources. Upon landing, their legs, specifically the tarsi, are equipped with taste receptors that allow them to “taste” the surface. Flies are opportunistic feeders, making them attracted to a wide array of organic materials, including ripe fruits, fermenting liquids, and animal waste.
What Happens When a Fly Lands
Once a fly lands on food, its actions are driven by its feeding and digestive processes. Since flies lack teeth, they cannot chew solid food. Instead, many common flies, like house flies, possess sponging mouthparts called a proboscis, designed to absorb liquids. If the food is solid, the fly must first convert it into a liquid form.
To achieve this, the fly commonly regurgitates digestive fluids, often referred to as “vomit,” onto the solid food. These enzyme-rich fluids begin to break down the food, liquefying it into a consumable “soup.” The fly then uses its proboscis to suck up this liquefied meal. This act of regurgitation can occur multiple times during a single meal. In addition to regurgitating, flies also commonly defecate as they feed.
The Unseen Dangers
The feeding habits and biology of flies make them effective mechanical vectors for various pathogens. As flies frequently land on unsanitary materials such as garbage, feces, and decaying organic matter, their bodies, legs, and mouthparts readily pick up bacteria, viruses, and parasites. These microorganisms cling to the tiny hairs and surfaces of the fly.
When a fly subsequently lands on human food, these collected pathogens can be transferred through physical contact. The act of regurgitating digestive fluids also directly contaminates the food with any microbes present in the fly’s digestive system. Similarly, defecation by the fly further deposits pathogens onto the food surface. Flies are known to spread a range of foodborne pathogens, including bacteria like E. coli and Salmonella, as well as those causing typhoid, dysentery, and cholera.