What Fuels a Fly? The Gross Truth About What Flies Eat

Whoops! You left the door open, and one of the world’s least favorite flying guests just zipped inside: the house fly. Flies are everywhere, buzzing around your food, waste, and everything in between. And while these creatures are small, their appetite is anything but (and also kind of gross). These swift, pesky insects might leave you wondering, what exactly fuels them? A fly’s diet perfectly suits its role in nature. From sugary spills to decaying matter, they thrive mostly on the things we toss aside. But how do they turn such unsavory substances into the energy they need to survive? Let’s take a closer look.

What Is a Fly?

Flies belong to the order Diptera. The term ‘fly’ is commonly used for any insect in this order, but not all flying insects are true flies. The order Diptera includes all true flies; the name means “two wings.” Specifically, true flies have one pair of wings for flying and a second pair, called halteres, which help them balance. There are over 120,000 species of flies, including houseflies, blowflies, fruit flies, gnats, hoverflies, and more.

A fly’s life span consists of four stages: egg, larva, pupa, and adult.

Egg: Flies typically lay their eggs on a moist substrate. This can be a dead animal or other decaying organic matter.

Larvae (maggots): The larvae of flies hatch from eggs as maggots. Maggots play a crucial role in decomposing organic matter, which makes it readily available for plants and other organisms. As maggots consume matter, they grow and molt, a process scientists refer to as ecdysis (shedding their exoskeletons). In doing so, they pass through various instar stages prior to forming a pupa.

Adult: Flies emerge from the pupa as adults to begin the cycle over again. Female house flies can lay up to 150 eggs per batch.

Now that we have detailed the stages of these animals and what they are, let’s get into the nasty part: their diet.

Fly Foods

Much of the fly diet consists of liquid or semi-liquid matter. This is important to note because they are unable to chew. The most common foods flies consume are:

• Rotting organic material
• Feces and manure
• Garbage/decomposing food
• Animal carcasses
• Sugary substances (fruit, nectar, even soda)

Depending on the fly species, some can be more selective of what they eat. For example, fruit flies tend to prefer fermented fruits or vinegar. What makes fruit flies attracted to fruit is the smell. Fruit flies also lay their eggs on ripening fruits, so their larvae have a food source. Blowflies specialize in feeding on decaying flesh, slurping the liquids from their dead food items.

Feeding and Looking For Food

Flies rely on their sense of smell, using their antennae to detect odors from far away. Using their feet as taste receptors, they can often be seen wiping them off to get a fresh taste. Once flies find a food source, some regurgitate digestive enzymes onto it. These digestive enzymes liquefy the food, making it easier for the fly to slurp it up with its proboscis (mouthpart). Forever on the move, flies are constantly sampling, landing, and tasting. As disgusting as their strange food preferences may sound, their feeding system is pretty unique. While eating, flies excrete waste constantly, which aids in fast digestion. Their proboscis is specialized to absorb even the finest liquids, such as yeast; in the case of mosquitoes, it is adapted to suck blood.

What’s the Point?

Despite their ick factor, flies play an important role in the ecosystem. Flies act as natural decomposers, breaking down waste and dead animals. This process, known as nutrient recycling, helps the environment in many ways. Specifically, when organic matter decomposes, the organisms that consume these nutrients make it readily available for the next generation of plants. In addition, natural decomposers such as flies remove waste from the ecosystem. Without the removal of waste, there would be an accumulation that would be detrimental to our ecosystems.

Threats Of A Fly

Although there are benefits to these creatures, they are not without risk. Houseflies can spread bacteria and disease through their feeding habits, such as E. coli, Salmonella, and dysentery. Within more urban areas, flies can adapt to their environment by living in households and landfills, proliferating with ease. To avoid flies in and around your home, sanitation is the first step. Remove trash that contains food or liquids, clean out your trash can, and eliminate areas that can be used for breeding.

Why We Need Flies

Flies are relentless eaters with one goal in mind: finding something smelly to slurp. With their straw-like mouthparts, unique digestion, and unusual feeding preferences, it’s hard not to be a little grossed out. It is important to note, though, that they still play a critical role in nature.

Flies provide important ecological functions that we need for a healthy environment. The recycling of matter is vital to removing waste and providing nutrients for the next generation of organisms. That said, whether cleaning up decay or spreading disease, these creatures are pretty much here to stay. So the next time a fly lands on your lunch, you’ll know both the foul and fascinating things they’re up to—and you’ll probably want to throw it away.