What Do Flies Eat?

Flies are an ever-present part of our environment. Whether you’re enjoying a picnic in the park, dining at a restaurant, or simply relaxing at home, chances are you’ve encountered these agile insects. Their ubiquity raises questions about their role in the ecosystem and, more specifically, what sustenance keeps them buzzing.

What do flies eat, and why do they seem to gravitate toward certain foods and locations? These questions have intrigued scientists, entomologists, and curious minds for centuries. Flies’ dietary preferences not only influence their behavior but also have implications for public health and hygiene. As we delve into the dietary habits of flies, we uncover a world of adaptability and opportunism that allows them to thrive in diverse environments.

Understanding Fly Nutrition

Delve into how flies classify as opportunistic feeders and their diverse dietary preferences.

The Classification of Flies as Opportunistic Feeders

Flies, as a taxonomic order known as Diptera, are remarkable opportunistic feeders. This classification means they don’t rely on a single, specialized food source but instead exhibit a flexible approach to nutrition. Their adaptability is a key survival strategy, allowing them to exploit various food resources as they become available.

Not the pest you are looking for?

Check out our pest library to see what other pests we have articles on

One prime example of this opportunistic behavior is the housefly (Musca domestica), a common household pest. Houseflies are known for their ability to feed on a wide range of substances, including sugary liquids, decaying organic matter, and even solid food particles. Their mouthparts, which consist of a sponging proboscis, enable them to lap up liquids and dissolve solid foods for ingestion. This adaptability ensures that they can find sustenance in diverse environments, from rotting fruit to pet food dishes.

Diverse Dietary Preferences Among Fly Species

While opportunism is a shared characteristic among flies, the dietary preferences of various fly species can differ significantly. Some flies are predominantly herbivorous, feeding on nectar and pollen from flowers. For instance, hoverflies (Syrphidae) are important pollinators that primarily consume floral nectar. Their role in pollination makes them valuable contributors to plant reproduction and agricultural ecosystems.

Conversely, other fly species are strictly carnivorous. Robber flies (Asilidae), for example, are formidable predators in the insect world. They capture other flying insects in mid-air and inject them with digestive enzymes, consuming the liquefied contents. These carnivorous flies play a crucial role in controlling pest populations and maintaining ecological balance.

Flies as Essential Contributors to Decomposition

Flies are not only opportunistic feeders but also vital contributors to the natural process of decomposition. Some fly species are attracted to decaying organic matter, such as dead animals and plant material. These flies, often referred to as carrion flies or saprophagous flies, lay their eggs on the decaying substrate. The larvae that hatch from these eggs, commonly known as maggots, feed voraciously on the decomposing material, accelerating its breakdown.

This role in decomposition serves an ecological purpose, as it helps recycle nutrients back into the ecosystem. Without flies and other decomposers, dead organic matter would accumulate, posing a significant environmental challenge. Flies’ ability to efficiently break down and recycle organic material underscores their importance in maintaining ecosystem health and balance.

Flies’ classification as opportunistic feeders, their diverse dietary preferences among species, and their role in decomposition shed light on the multifaceted nature of these insects. Their adaptability and ecological contributions make them not only a subject of scientific intrigue but also a crucial component of our natural world.

Flies’ Preferred Food Sources

Examine the solid vs. liquid food choices of flies and what common liquids attract them.

Solid vs. Liquid Food Sources

Flies display remarkable versatility when it comes to their food sources, with a distinct preference for either solid or liquid substances. This adaptability enables them to exploit a wide range of environments and food options. 

Some fly species, such as the housefly, are known for their ability to feed on solid foods. Their mouthparts allow them to chew and dissolve solid particles, making them efficient scavengers. Solid food sources for flies may include decaying fruits, vegetables, meats, or even fecal matter.

Flies like fruit flies are more inclined toward liquid foods. They possess specialized mouthparts that can sponge or lap up liquids, making them particularly attracted to sugary substances, overripe fruits, and fermenting liquids.

Common Liquids that Attract Flies

The sweet scent of sugary liquids, such as fruit juices, nectar, or sugary spills, acts as a potent magnet for many fly species. Fruit flies, in particular, are notorious for their attraction to ripe fruits and sweet beverages. Flies, especially carrion flies, are strongly attracted to liquids emanating from decomposing matter, such as carcasses or rotting plant material. The odors released during decomposition serve as chemical cues for flies to locate suitable breeding sites.

Fermenting liquids, often associated with alcoholic beverages or overripe fruit, can also be highly appealing to flies. They are drawn to the fermentation byproducts and the rich bouquet of scents these liquids produce.

Detecting Suitable Food Sources from a Distance

Flies possess highly sensitive antennae equipped with olfactory receptors. These receptors can detect minute quantities of volatile organic compounds emitted by potential food sources. For example, the aroma of ripe fruit or the chemical signals from decaying matter can guide flies to their next meal.

Some fly species are also adept at using visual cues to find food. Brightly colored or visually distinct fruits and liquids can catch their attention, especially in open environments. Flies can sense and analyze chemical cues that signal the presence of suitable food. These cues can include pheromones released by other flies or specific chemical compounds released during the initial stages of decomposition.

The Anatomy of Fly Feeding

Uncover the intricate mechanisms through which flies use their mouthparts to feed and extract nutrients from various foods.

How Flies Use Their Mouthparts to Feed

Flies have evolved a remarkable set of mouthparts adapted to their varied dietary preferences. These mouthparts play a crucial role in facilitating feeding, and their structure can vary depending on the type of food they consume. Many fly species, like houseflies, possess a sponging proboscis. This proboscis is essentially a tubular, straw-like structure that they use to feed on liquid substances. It functions by extending into the liquid and absorbing it through tiny channels. Flies can then draw the liquid up through capillary action.

For flies that feed on solid substances, such as decomposing matter or feces, their mouthparts are adapted for chewing. They can use their mandibles to break down solid particles. Saliva containing digestive enzymes helps dissolve the food, creating a semi-liquid substance that can be ingested.

Extracting Nutrients from Various Foods

Flies are efficient at extracting nutrients from the diverse range of foods they encounter, whether it’s the sugars in nectar or the proteins in decaying matter.

  • Digestive Enzymes – Flies produce digestive enzymes that play a crucial role in breaking down the food they consume. These enzymes start the process of digestion by breaking complex molecules into simpler, more easily absorbed forms.
  • Filter Feeding – In the case of liquid-feeding flies, their sponging proboscis not only absorbs liquids but also filters out particles. This allows them to ingest dissolved nutrients while avoiding solid debris.
  • Efficient Nutrient Absorption – The fly’s digestive system is adapted for efficient nutrient absorption. After initial digestion, nutrients are absorbed through the walls of the fly’s midgut and transported to the rest of the body, providing energy for their activities.

Can Flies Taste Their Food?

Yes, flies can taste their food, albeit in a somewhat different manner than humans. Flies have taste receptors, primarily located on their feet and proboscis. These taste receptors allow them to assess the chemical composition of the substances they encounter.

  • Feet Tasting – Fly taste receptors on their feet are known as chemoreceptors. When they land on a potential food source, they extend their proboscis and tap the surface to sample the chemicals present. This helps them determine whether the substance is suitable for feeding.
  • Proboscis Tasting – Flies can also taste their food by probing it with their proboscis. They secrete a small amount of saliva containing digestive enzymes onto the food to begin the process of breaking it down. The taste receptors on the proboscis can then assess the chemical composition of the food, helping the fly decide if it’s worth consuming.

Flies’ feeding mechanisms are highly specialized, allowing them to adapt to a wide range of food sources. Whether they are sponging up nectar or breaking down decaying matter, their mouthparts and sensory organs play crucial roles in their ability to feed efficiently.

Dietary Adaptations and Preferences

Discover how flies adapt to different diets, from fresh to decaying organic matter and sweet to savory foods.

Fly Preference for Fresh or Decaying Organic Matter

Flies exhibit intriguing dietary adaptations when it comes to the freshness of their food sources. While some species have a preference for fresh, living plant material, others thrive on decaying organic matter. Certain fly species, like flower flies (Syrphidae), primarily feed on fresh, living plant material, such as nectar and pollen. Their specialized mouthparts are designed for sipping nectar from flowers, making them valuable pollinators in many ecosystems.

In contrast, other fly species are attracted to decaying organic matter, including dead animals, rotting fruits, and compost. These flies, often referred to as carrion flies or saprophagous flies, are equipped with mouthparts and sensory adaptations that help them locate and feed on decaying substances. Their presence accelerates the decomposition process, aiding in nutrient recycling.

Sweet vs. Savory: What Flies Favor

Flies, like humans, have preferences when it comes to taste, and these preferences are often divided into sweet and savory categories. Many fly species are drawn to sweet substances. Sugary liquids, such as nectar, honeydew, or fruit juices, are particularly appealing to them. Fruit flies, for instance, are renowned for their attraction to ripe and fermenting fruits due to their high sugar content.

On the savory side, flies can also be attracted to protein-rich sources. This includes decaying animal matter, feces, or other sources rich in proteins. Carrion flies, for example, are aptly named for their preference for carrion and other proteinaceous food sources.

Unique Dietary Traits of Houseflies and Fruit Flies

Houseflies are known for their versatile dietary habits. They are opportunistic feeders and can thrive on a wide range of food sources, including sugary liquids, decaying matter, and even solid foods. Their adaptability to human environments has earned them a reputation as household pests, as they are often found around food, garbage, and excrement.

Fruit flies, on the other hand, are typically associated with fresh or fermenting fruits. Their specialized proboscis is designed for piercing the skin of fruits and sipping the sugary juices within. This makes them a nuisance in kitchens and fruit-bearing environments. While they may seem to have a sweet tooth, fruit flies also consume microorganisms associated with the fermenting process, contributing to their diet’s complexity.

Flies and Disease Transmission

Investigate the potential for flies to transmit diseases and the importance of controlling their populations around food.

Can Flies Transmit Diseases Through Their Feeding Habits?

Flies have long been associated with the potential transmission of diseases due to their feeding habits and behavior. While they are not disease vectors in the same way as mosquitoes or ticks, flies can indirectly contribute to the spread of diseases.

Mechanical Transmission

Flies, especially houseflies, can carry pathogens such as bacteria and viruses on their body hairs and mouthparts. When they land on contaminated surfaces, like feces, garbage, or decaying matter, they can pick up these pathogens. If they subsequently land on food or food preparation surfaces, they can transfer these pathogens, potentially leading to foodborne illnesses.

Contaminating Food and Surfaces

Flies regurgitate and defecate frequently while feeding. This behavior can further contaminate the surfaces and food they come into contact with. Pathogens present in their saliva or feces can find their way into the food chain, posing health risks to humans.

The Importance of Controlling Fly Populations Around Food

Flies’ presence near food can lead to contamination with harmful pathogens. This contamination can result in foodborne illnesses, with symptoms ranging from mild gastrointestinal discomfort to severe illness. In food-related establishments such as restaurants, kitchens, and food processing facilities, controlling fly populations is crucial to ensuring hygienic conditions. Fly infestations can lead to regulatory violations and reputation damage.

Flies have the potential to transmit diseases not only through food but also by landing on surfaces and subsequently coming into contact with humans. Effective fly control measures are essential to reduce the risk of disease transmission in both domestic and commercial settings. In agricultural settings, certain fly species can damage crops and reduce yields, leading to economic losses. Implementing pest control measures is necessary to protect crop productivity.

Fly Diet and the Ecosystem

Flies, often perceived as common pests, play crucial roles in maintaining ecological balance in various ecosystems. Their contributions are multifaceted and extend beyond their role as mere opportunistic feeders. Flies are primary contributors to the decomposition of organic matter. They assist in breaking down dead animals, plant materials, and other organic detritus. Their larvae, commonly known as maggots, voraciously consume decaying matter, accelerating its decomposition. This decomposition process not only recycles nutrients back into the ecosystem but also helps prevent the accumulation of organic waste, thereby promoting overall ecosystem health.

By breaking down organic matter, flies release nutrients into the environment. These nutrients, such as nitrogen and phosphorus, become available to plants and other organisms, contributing to nutrient cycling within ecosystems. This nutrient recycling ensures that essential elements are continually available for the growth of new organisms. Flies are integral components of food webs. They serve as a source of food for various predators, including birds, spiders, and other insects. The presence of flies in the diet of these predators helps regulate their populations, contributing to the overall balance of predator-prey dynamics in ecosystems.

The Role of Flies in Pollination and Decomposition

While some flies are primarily scavengers, others are important pollinators. For instance, hoverflies are significant pollinators in many ecosystems. As they visit flowers in search of nectar, they inadvertently transfer pollen from one flower to another, facilitating plant reproduction. This pollination service is essential for the production of fruits and seeds in numerous plant species, including many that are important for agriculture.

Flies are among nature’s most efficient decomposers. Carrion flies and saprophagous flies play essential roles in breaking down and recycling organic matter. Without their contributions, dead animals and plant materials would accumulate, creating ecological imbalances and potential health hazards.

Flies are more than just pests; they are ecological contributors that participate in vital processes such as decomposition, nutrient cycling, and pollination. Their roles in ecosystems are interconnected, and their presence is essential for maintaining the delicate balance of nature. Understanding and appreciating these roles can lead to a more holistic view of these often misunderstood insects in the natural world.

Unusual Dietary Habits

Explore the unusual dietary behaviors of flies, including blood-feeding habits and harmful foods.

Can Flies Feed on Blood? Species That Do So

While the majority of fly species are not blood-feeders, there are specific species that have adapted to feed on blood. These hematophagous flies have specialized mouthparts for piercing the skin of their hosts and feeding on blood. Two notable groups of blood-feeding flies are:

Tsetse Flies

Tsetse flies are found in sub-Saharan Africa and are known for their ability to transmit African trypanosomiasis, a parasitic disease that affects humans and animals. They feed exclusively on the blood of vertebrate hosts, including humans, and use their proboscis to pierce the skin and access blood vessels.


Sandflies are responsible for transmitting diseases such as Leishmaniasis, which affects humans and other mammals. Female sandflies are blood-feeders and use their specialized mouthparts to puncture the skin and obtain a blood meal. Sandflies are found in various regions, including parts of Africa, Asia, and the Americas.

Toxic or Harmful Foods for Flies

Flies, like many other organisms, can be affected by toxic or harmful substances in their environment. While they are adapted to feed on a wide range of organic materials, there are certain substances that can be toxic to flies:

  • Chemical Insecticides – Flies can be susceptible to chemical insecticides used for pest control. Insecticides that come into contact with flies can disrupt their nervous systems, leading to paralysis or death.
  • Toxic Plants – Flies that feed on plant materials may encounter toxic or poisonous plants. Ingesting toxic plant matter can be harmful or fatal to flies.
  • Pathogenic Microorganisms – Flies can carry and transmit pathogenic microorganisms, such as bacteria and viruses. In some cases, these microorganisms can harm the flies themselves, causing diseases or impairing their health.
  • Inedible Substances – Flies may encounter inedible or indigestible substances in their environment, such as plastics or synthetic materials. Ingesting such materials can be harmful and may lead to physical blockages in their digestive systems.

It’s important to note that flies have evolved mechanisms to detect and avoid toxic or harmful substances, and they are generally resilient insects. However, their exposure to such substances can still have adverse effects on their health and survival. Additionally, the presence of toxic substances in their environment can impact their role as disease vectors or scavengers in ecosystems.


While flies play critical roles in nutrient cycling, pollination, and decomposition in natural ecosystems, they can also pose challenges in human environments. Controlling fly populations is of paramount importance to ensure public health, food safety, and overall hygiene. Flies have the potential to transmit diseases, contaminate food, and disrupt daily life in residential and commercial spaces. The world of fly diets is a captivating journey into the adaptability and complexity of these often-overlooked insects. Understanding their dietary habits enhances our appreciation of their ecological significance while emphasizing the need for responsible fly management to ensure the well-being of both humans and the environment.