Fruit flies (Drosophila melanogaster) are tiny insects often found in homes, especially around decaying organic matter. These small, tan-bodied flies with red eyes are a common sight, leading to questions about their feeding habits. This article clarifies the actual diet of fruit flies and their interactions with various organic materials.
The True Diet of Fruit Flies
Fruit flies primarily consume fermenting fruits, vegetables, and other sugary substances. They are highly attracted to the yeast and bacteria that drive fermentation, breaking down complex sugars into digestible forms. This includes overripe produce, spilled alcoholic beverages, and various fermentation byproducts. Adult flies feed on these decaying materials, and females lay their eggs within them.
Larvae also feed on the yeast in rotting fruit. Beyond fruits, their diet extends to plant secretions, honeydew from aphids, fungi, and organic residue in unclean drains. These insects are considered nutritional generalists, adapting their consumption based on carbohydrate availability. This dietary preference highlights their reliance on the specific chemical changes that occur during fermentation.
Why Feces is Not on Their Menu
Fruit flies generally do not consume feces because it lacks the specific nutritional components they require. Feces does not undergo the type of fermentation that produces the sugars and yeasts essential for their diet. The microbial communities in fecal decomposition differ significantly from those in fermenting plant matter, making it an unsuitable food source for Drosophila melanogaster.
Feces often contain harmful bacteria and pathogens detrimental to fruit flies, whose digestive systems are adapted for processing fermenting plant material. Their biological machinery is not equipped to efficiently extract nutrients from fecal matter. Therefore, feces does not align with the specific dietary needs or physiological adaptations of fruit flies.
Understanding Fruit Fly Attraction
While fruit flies do not eat feces, they are drawn to decaying organic matter that produces fermenting odors. Their keen sense of smell, facilitated by specialized olfactory receptors, guides them to these sources. They are particularly attracted to volatile compounds like acetic acid and ethanol, which are byproducts of yeast and bacterial activity during fermentation. This explains why they might appear near garbage or other organic waste, even if not consuming the waste itself.
Other types of flies, such as house flies, blowflies, and flesh flies, feed on and lay eggs in feces, utilizing its fats, proteins, and minerals. These “filth flies” have different dietary specializations. They should not be confused with fruit flies, which specifically seek the sweet, yeasty aromas of fermenting plant material for sustenance and breeding.