Flies appear to “taste” surfaces they land on using their feet. This isn’t just an illusion; flies do indeed possess specialized sensory structures on their legs that allow them to detect chemicals in their environment. This ability is a fascinating adaptation that plays a role in their survival and feeding behaviors.
The Science of Fly Taste
Flies possess chemoreceptors, which are sensory receptors that detect chemical stimuli, located on various parts of their bodies. A significant concentration of these chemoreceptors resides on their tarsi, the last segments of their legs, analogous to our feet. These structures are equipped with tiny hairs called sensilla, which house gustatory receptor neurons (GRNs). When a fly lands on a surface, these sensilla make direct contact, allowing the GRNs to detect dissolved sugars, salts, and other chemical compounds.
The process of tasting involves the detection of non-volatile compounds through these contact chemoreceptors. If the fly’s tarsal chemoreceptors identify something palatable, such as sugar, this triggers a reflex known as the proboscis extension reflex (PER). The proboscis, a tube-like mouthpart, then extends, allowing the fly to further sample and potentially ingest the food source. This initial “taste” with their feet is a rapid assessment, guiding their feeding decisions.
Why Flies Taste with Their Feet
The ability of flies to taste with their feet provides distinct evolutionary advantages. This adaptation allows them to quickly identify potential food sources without fully committing to landing or ingesting them. By sampling a surface with their tarsi, flies can assess the nutritional value and detect any harmful substances present, enabling rapid decision-making in diverse environments.
This rapid assessment is particularly beneficial for efficient foraging. Given their small size and the need for quick resource discovery, tasting with their feet allows flies to maximize their feeding opportunities while minimizing exposure to dangers. For instance, if a fly detects a sweet substance with its leg, it automatically extends its proboscis to consume it. This mechanism helps them avoid consuming toxic chemicals and guides them toward nutrient-rich foods.
Beyond the Feet: Other Sensory Organs
While the feet are primary organs for taste detection in flies, their gustatory system extends to other body parts, providing a comprehensive assessment of their environment. Flies also possess taste receptors on their mouthparts, specifically the labellum, which acts like a tongue, and internal pharyngeal organs. These additional receptors allow for a more thorough evaluation of food once it has been contacted or even before full ingestion.
Taste sensilla are also found on their antennae, wing margins, and even the ovipositor in females. These various taste organs work in conjunction with the foot receptors, contributing to a complete sensory experience. For example, while leg receptors might prompt a fly to stop and consider a food source, the mouthpart receptors play a further role in the decision to consume it. This distributed sensory network enhances the fly’s ability to navigate its chemical world, guiding behaviors related to feeding, mating, and egg-laying.