Do Flies Throw up When They Land on You?

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Flies: those persistent, buzzing creatures that seem to have an uncanny knack for ruining picnics and indoor gatherings. 

But beyond the annoyance, have you ever paused to wonder what happens when they land on you? 

There’s a popular belief that flies vomit every time they touch down, but how much truth is there to this claim? 

In this article, we’ll delve into the fascinating world of fly anatomy, their unique feeding habits, and the implications of their behaviors on our health.

Do Flies Throw up When They Land on You?
Large Female Horse Fly

Fly Anatomy and Feeding Habits

Flies, belonging to the order Diptera, are equipped with a unique anatomy that allows them to feed on a wide variety of substances, from organic matter to liquid sustenance. 

Understanding their anatomy is crucial to comprehending their feeding habits.

Digestive System

Flies have a simple digestive system that consists of a foregut, midgut, and hindgut. 

The foregut stores food, the midgut is where digestion primarily occurs, and the hindgut absorbs water and excretes waste.

Mouthparts – The Proboscis

Unlike many other insects, flies don’t have chewing mouthparts. Instead, they possess a specialized mouthpart called a proboscis, which functions like a sponge. 

This sponging mouthpart allows them to soak up liquid food. 

The proboscis is highly adapted to lap up liquids and can even soak up minute food particles from surfaces.

Preference for Liquid Food

Flies primarily feed on liquids because they can’t ingest solid food in the same way that many other creatures do. 

They are attracted to a range of substances, from sugary solutions like nectar or spilled soda to more unsavory sources like decaying organic matter or excrement.

Regurgitation and Digestion

When faced with solid food, flies employ a unique method to consume it. They regurgitate digestive enzymes onto the solid food. 

These enzymes break down the food, turning it into a liquid form. Once liquefied, the fly can then lap up the substance with its proboscis. 

This process not only aids in digestion but also allows flies to “taste” their food.

Feeding Range

Flies are not particularly picky eaters. They can feed on a range of substances, including decaying organic matter, feces, fermenting fruit, and even the wounds of living animals. 

Their ability to feed on various substances, combined with their rapid reproduction rate, makes them both versatile and, at times, problematic, especially when considering issues of sanitation and disease transmission.

Tiger Bee Fly

Do Flies Throw up When They Land on You?

Yes, they do. Flies have a fascinating and somewhat unsettling method of feeding that involves regurgitation

Here’s a closer look at why flies regurgitate

Digestion of Solid Foods

Flies, especially common houseflies, are equipped with mouthparts that are designed to soak up liquid food. 

However, they often land on solid food sources, such as crumbs or organic matter.

To feed on these solids, flies regurgitate digestive enzymes from their stomach onto the food. 

These enzymes break down the solid food into a liquid form, making it consumable for the fly. In essence, they are externally pre-digesting their food.

Tasting Their Food

Regurgitation also serves a sensory purpose. By expelling a small amount of digestive fluid onto potential food sources, flies can “taste” and assess the quality of the food. 

If the food is suitable, they will continue the process of liquefying and consuming it.

Storing Food for Later

Flies can consume more food than they can immediately digest. 

When they ingest excess liquid food, they might regurgitate it later when they need nourishment. 

This behavior can be likened to a form of storage, ensuring they have a food source when options are scarce.

Avoiding Toxic Substances

If a fly ingests something harmful or toxic, regurgitation acts as a mechanism to expel the harmful substance. 

This behavior can be a lifesaving reaction, preventing the ingestion of potentially lethal compounds.

Horse Fly
Horse Fly

Feeding Offspring

Some species of flies regurgitate food to feed their offspring

The pre-digested food provides young flies with essential nutrients in a form that’s easy for them to consume and process.

Other Unsavory Habits of Flies

Flies have a reputation for being unsanitary and even repulsive. Their feeding habits, which involve regurgitation, are just the tip of the iceberg. 

Here are some other unsavory behaviors and characteristics of flies that contribute to their unpopularity

Feeding on Decaying Matter

Flies are scavengers and are often attracted to decaying organic matter. 

This includes rotting food, dead animals, and even feces. Such feeding habits make them potential carriers of harmful pathogens.

Laying Eggs in Organic Waste

Many fly species, including the housefly, lay their eggs in decaying organic matter. 

This provides a food source for the emerging larvae. Unfortunately, this often includes garbage, dung, and carcasses.

Tarsal Taste Buds

Flies taste with their feet. When they land on various surfaces, including food, trash, or excrement, they’re essentially “tasting” it. 

This behavior can lead to the transfer of harmful bacteria from one surface to another.

Rapid Reproduction

Flies reproduce at an astonishing rate. A single pair of houseflies can produce more than a million offspring in just a few weeks under optimal conditions. 

This rapid reproduction can lead to infestations and increased potential for disease transmission.

Carriers of Disease

Due to their attraction to waste and decaying matter, flies can pick up and transmit a range of diseases. 

They can carry bacteria like Salmonella and E. coli, as well as other pathogens that can cause illnesses like typhoid, cholera, and dysentery.

Short Lifespan but High Activity

While flies typically have a short lifespan, often just a few weeks, they are highly active during this time. 

A single fly can land on numerous surfaces in a short period, increasing the potential for spreading contaminants.

Hover Fly

Defecation Habits

Flies defecate frequently, sometimes every couple of minutes. If they’re inside a home or around food, this can lead to contamination.

Attraction to Open Wounds

Some species of flies, like the blowfly, are attracted to open wounds in animals and humans. 

They can lay eggs in these wounds, leading to conditions like myiasis, where fly larvae grow and feed inside the host’s tissue.

Health Implications

Here’s a closer look at the health implications associated with flies

Transmission of Diseases

Flies can carry bacteria, viruses, and other pathogens on their bodies and in their saliva, feces, and vomit. 

When they land on food, utensils, or surfaces, they can transfer these pathogens, leading to potential outbreaks of diseases.

Common Diseases Spread by Flies

  • Gastrointestinal infections: Flies can transmit bacteria like Salmonella, Shigella, and E. coli, which can cause symptoms like diarrhea, vomiting, and stomach cramps.
  • Typhoid Fever: Caused by the Salmonella typhi bacteria, this disease can lead to high fever, weakness, and abdominal pain.
  • Cholera: Flies can spread the Vibrio cholerae bacteria, leading to severe diarrhea and dehydration.
  • Dysentery: Both bacterial and amoebic forms of dysentery can be spread by flies, causing bloody diarrhea and other symptoms.

Parasitic Infections

Some flies can transmit parasitic worms. For instance, the sandfly can transmit the parasite responsible for Leishmaniasis, a disease that affects the skin and internal organs.

Secondary Infections from Wounds

Flies, especially those attracted to open wounds, can introduce bacteria into the wound, leading to secondary bacterial infections. This can delay healing and lead to further complications.

Allergic Reactions

Some individuals may be allergic to fly bites, especially from certain species like black flies or horseflies. 

Reactions can range from mild itching and redness to more severe symptoms like swelling, blistering, and, in rare cases, anaphylaxis.

Bathroom Fly

Economic Implications

In areas where flies transmit diseases that affect livestock, there can be significant economic losses. Infected animals may produce less milk, lose weight, or, in severe cases, die.

Food Contamination

Flies landing on food can lead to contamination, making the food unsafe for consumption. 

This not only poses health risks but can also lead to economic losses for businesses, especially those in the food industry.

Preventative Measures

Preventing fly infestations is crucial not only for comfort but also for health reasons. Here are some effective preventative measures to keep flies at bay

Proper Sanitation

Regularly clean and disinfect your home, especially the kitchen and dining areas. Ensure that food residues, especially sugary substances, are cleaned up immediately.

Waste Management

  • Ensure that trash bins have tight-fitting lids.
  • Dispose of garbage regularly and keep waste areas clean.
  • Use compost bins for organic waste, but make sure they are well-sealed and placed away from the main living areas.

Food Storage

  • Store food in sealed containers or in the refrigerator.
  • Keep fruits and vegetables covered or stored properly, especially if they are overripe, as they can attract flies.

Window and Door Screens

  • Install or repair screens on windows and doors to prevent flies from entering homes.
  • Ensure that there are no gaps or holes in the screens.

Fly Traps and Electric Fly Zappers

  • These can be used to trap and kill flies, especially in areas where they are prevalent.
  • Ensure they are placed in strategic locations, away from food preparation areas.

Natural Repellents

  • Plants like basil, lavender, and mint can act as natural fly repellents. Consider planting them around entrances or in pots indoors.
  • Essential oils, such as eucalyptus or citronella, can also deter flies when diffused.

Limit Outdoor Lighting

  • Flies and other insects are attracted to light. If possible, reduce outdoor lighting during peak fly activity times or use yellow “bug lights” which are less attractive to flies.

Water Management

  • Ensure there’s no stagnant water around your property, as it can be a breeding ground for certain fly species.

Regular Home Maintenance

  • Seal cracks and crevices in walls, windows, and doors to prevent flies from entering.
  • Check for and repair any leaks in the roof or walls, as moisture can attract flies.

Professional Pest Control

  • If you have a persistent fly problem, consider seeking help from professional pest control services. They can provide specialized treatments and advice tailored to your specific situation.

By implementing these preventative measures, you can significantly reduce the risk of fly infestations in your home and surrounding areas. Remember, a proactive approach is always more effective than dealing with an established infestation.


In the intricate world of flies, their regurgitative feeding habits might seem unsettling, especially when they land on us. 

While it’s a myth that they always vomit upon landing, their feeding process does involve regurgitation.

 Beyond this, flies can carry pathogens, underscoring the importance of good hygiene and preventive measures. 

By understanding their behavior and taking proactive steps, we can minimize potential health risks and coexist with these ubiquitous insects in a safer environment.

Reader Emails

Over the years, our website, has received hundreds of letters and some interesting images asking us about these insects. Scroll down to have a look at some of them.

Letter 1 – Puking Blue Bottle Fly

Subject:  What is this, and what is it drinking?
Geographic location of the bug:  Iowa- north Central
Date: 10/07/2017
Time: 11:45 PM EDT
This bug caught my eye.  I can only identify  a handful of bugs.   So forgive me if this is fairly common.   It looked like a hairy “hulk” for a house fly.
How you want your letter signed:  Bug Novice

Vomiting Blue Bottle Fly, we believe

Dear Bug Novice,
This is definitely a Fly in the order Diptera, and we recall reading once that Flies regurgitate their food, so we searched the web and found this image on Ask an Entomologist of a regurgitating Fly and the site states: 

“You’ve probably noticed an intrepid fly boldly navigating your pizza, lapping up oils and pizza sauce.  Shortly after enjoying some of your meal, the fly, assuming it’s the kind with the lapping mouth parts, will have to throw it’s food back up and eat it again.

If it’s walking on something solid, like your steak, it has to spit a digestive soup on it to help break it down.”  Kids’ Animal Station has a similar image with this explanation:  “Flies taste with their feet, so, if they think you taste good, (keep in mind that, from a fly’s perspective, dog poop tastes good, so you’d better hope the fly doesn’t think you taste good!) they might just vomit stomach juices on you in an attempt to liquefy your skin into something fly edible.

Luckily, house fly vomit is not actually strong enough to break down human skin, but you still have to think about that tiny speck on your arm or leg that could carry disease.”  We don’t immediately recognize your fly, and its red vomit is quite eye-catching, so we will attempt to identify it.

Update:  Shortly after posting your submission, we found posting of a Blow Fly that looks like your individual on The Backyard Arthropod Project , and the speculation is that it might be Calliphora livida, but we would rather hope your individual might be a Blue Bottle Fly, Callipphora vomitoria, which is pictured on BugGuide, and whose scientific species name alludes to the possibility that it might be a frequent puker. 

Alas, no BugGuide images illustrate the regurgitation process, and no mention is made on BugGuide regarding the meaning of its binomial name.

Interesting!  Thank you for your knowledge.
Originally I took the picture to send to my son who was visiting Grandma that day.   I now wish I would have taken different angles, because this fly has intrigued me since I saw it.

Unfortunately I think you may be right on this blow fly.   (However I don’t recall color.  I could be  mistaken)  We live in farm land, surrounded by thousands (maybe million) chickens, as well as pigs.   

In addition these confinements have manure storage unfortunately close (within 5 miles) to our home.    We have had an increase of weeds and flies because of it.
Thank you again!


  • Bugman

    Bugman aka Daniel Marlos has been identifying bugs since 1999. is his passion project and it has helped millions of readers identify the bug that has been bugging them for over two decades. You can reach out to him through our Contact Page.

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  • Piyushi Dhir

    Piyushi is a nature lover, blogger and traveler at heart. She lives in beautiful Canada with her family. Piyushi is an animal lover and loves to write about all creatures.

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Tags: Blow Fly

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