The small, dark specks flies leave on surfaces confirm that they produce waste. Flies poop with remarkable frequency due to their rapid metabolism and liquid diet. Since they consume only liquefied food, their digestive cycle moves quickly, necessitating frequent stops to both feed and excrete waste products.
The Fly Digestive System
Flies do not possess teeth, so they engage in external digestion. This process begins when the fly regurgitates a mixture of saliva and digestive enzymes onto a potential food source. This fluid rapidly breaks down solid organic matter, dissolving it into a liquid the fly can ingest. The fly then uses its spongy, straw-like mouthpart, the proboscis, to suck up the liquefied meal.
Once consumed, the liquid food first enters the crop, a temporary storage organ. The crop is primarily a holding area and is not the main site of digestion, meaning it lacks the necessary enzymes to neutralize ingested pathogens. Food is then gradually moved into the midgut, where the bulk of nutritional absorption and chemical breakdown occurs.
Frequency and Visibility of Waste Spots
The numerous small spots seen on surfaces are evidence of the fly’s short digestive cycle, which can be completed in minutes. Flies often deposit waste immediately after or even during a meal. This behavior is driven by the need to quickly eliminate excess water and undigested material.
Flies leave two types of spots: regurgitation and feces. Regurgitation spots are typically lighter in color and more circular, resulting from the fly depositing excess fluid or enzyme-laden saliva. Fly feces, or flyspeck, are the true waste products. These are small, dark-colored specks, often brown or black, and may have a slightly elongated shape. The darker color comes from the concentrated, processed remnants of the fly’s meal, which may include digested blood or unsanitary organic matter.
Health Implications of Fly Feces
The waste products left by flies carry public health implications because flies are mechanical vectors of disease. When a fly lands on unsanitary materials, such as animal feces or decaying matter, it picks up bacteria and viruses on its body. These pathogens are then ingested along with the fly’s meal and pass through the digestive system.
Both fly feces and vomit act as primary transmission pathways, depositing these collected pathogens onto surfaces and food. Flies can spread disease-causing organisms, including bacteria that cause food poisoning like Salmonella and Escherichia coli. Other examples of diseases transmitted through fly waste include dysentery, cholera, and typhoid. The risk to human health increases when these contaminated spots are left on food, allowing pathogens to multiply before consumption.