Eating Habits of Fruit Flies

The feeding habits of the common fruit fly (Drosophila melanogaster) are ever-changing. Its eating patterns change because of sensory stimuli, metabolic needs, nutrient signals and internal feeding cues triggered by insulin-like peptides. In the wild, they feast on yeast and bacteria from rotting or ripe fruit. In the lab, they eat yeast cells growing on carbohydrates and sugars. Fruit flies don't just eat for the sake of eating. They have body sensors that detect carbohydrates and proteins inside the food, and the flies respond by shifting feeding behaviors to match the specific food.

A fruit fly's attraction to food is regulated by its hormones and physiological cues. It carries its taste receptors on its long tongue, called a proboscis, which signals the fly's brain to eat or not to eat. This fly hovers near overripe fruit or decaying vegetables. It also has a taste for fermenting sugars and alcohol and settles comfortably inside root or wine cellars or unrefrigerated vegetable storage houses. Hungry fruit fly maggots can eat through an entire strawberry crop or banana plantation and then head toward a succulent cacti plant.

Inside the fly's mouth is a long, thin, tongue-like feeding tube that can extend or retract when the fly wants to taste something. This proboscis tastes and ingests food by sucking on it like a straw. Although the fly can only ingest liquids, it has chemicals in its spit or vomit to change some solids into liquids. Inside its taste sensory cells, it has an internal daily biological clock telling the fly when and how much to eat. These clocks seem to regulate eating binges during certain times of the day; i.e., flies eat more sugar during the day and less at night.

The adult fruit fly lays its eggs in the fresh flesh of a fruit or vegetable. Drosophila flies do not break the skin of the fruit or veggie but look for cracked or slightly ripened fruit to deposit their eggs. The eggs hatch into larvae called maggots which feed instantly on the surrounding pulp of its birth chamber walls. The maggots continue to eat this pulp until they mature in about five days as the fruit starts to rot. Satiated maggots will then crawl out of the mushy sludge, hatch into adult flies and repeat the cycle.

A fruit fly can also find a cozy corner in homes, restaurants, supermarkets or any moist environment with rotting or fermenting organic material. Once inside a home, they adapt eating habits to coincide with some pretty strange, crazy nutrients. For instance, they adjust tastes to survive on drain slime or sour mop residues. They can spend their entire life cycle feeding on a food glob in a floor crack or sparsely subsist on a gaseous diet of alcohol or yeast fumes. The reason their body can flourish on weird diets is because it makes a special chemical that changes alcohol into temporary nourishment before poisoning the fly.