Flies are a diverse group of insects with varied feeding behaviors. Their diets vary significantly among species, ranging from common household pests to specialized predators and parasites. Understanding their diets provides insight into their ecological roles, which can be surprising given their often-unwanted presence.
Common Dietary Habits of Flies
Many common fly species, such as house flies and fruit flies, are attracted to decaying organic matter and sugary liquids. House flies, for instance, are general feeders that consume a wide variety of substances, including food waste, animal waste, and rotting fruit and vegetables. Their strong sense of smell draws them to decomposing materials, which also serve as breeding grounds for their larvae.
Fruit flies, as their name suggests, are primarily drawn to fruit, especially when it is overripe or fermenting. They feed on microorganisms, such as yeast, that grow on the surface of decaying produce. This attraction extends to other sugary substances like spilled alcoholic beverages, plant sap, and aphid honeydew. Blow flies, characterized by their metallic sheen, feed on and develop within fresh or decaying meat and animal carcasses.
How Flies Consume Food
The specific mouthparts of a fly determine how it consumes its food. Many common flies, including house flies and fruit flies, possess sponging mouthparts. These mouthparts consist of a fleshy, elbowed labium that ends in sponge-like structures called labella. When a fly encounters solid food, it regurgitates saliva containing digestive enzymes to liquefy it externally. The liquefied food is then drawn into the esophagus through minute channels within the labella by capillary action.
Other fly species have piercing-sucking mouthparts. Mosquitoes, for example, have modified mouthparts forming a proboscis to pierce skin and suck blood. While female mosquitoes feed on blood, males consume nectar. Similarly, some predatory flies use piercing-sucking mouthparts to subdue prey, injecting digestive enzymes to liquefy internal tissues before ingesting them.
Diverse Diets Across Fly Species
Beyond common feeding habits, flies exhibit remarkable dietary diversity. Robber flies are predators that hunt other insects, including beetles, grasshoppers, butterflies, bees, and even other flies. They employ a sit-and-wait strategy, ambushing prey mid-air and injecting neurotoxins and digestive enzymes before consuming the liquefied contents.
Some flies have parasitic lifestyles. Tachinid flies, for instance, are parasitic flies whose larvae develop inside other insects, ultimately killing their hosts. These larvae absorb nutrients from the host’s internal fluids, saving vital organs for last. Adult tachinid flies often feed on flower nectar.
Fungus gnats are commonly found near houseplants, where their larvae feed on fungi and decaying plant material in the soil. While adults are harmless, their larvae can sometimes damage plant roots when populations are high.