Do Flies Poop When They Land? Uncovering the Insect’s Habits

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Flies are often unwelcome guests, particularly when they land on our food. Many people wonder if these insects contaminate our meals with their waste or regurgitated digestive juices. To answer that question, we need to delve into the behavior of flies and learn how they interact with their environment.

When flies land on surfaces, including food, they might excrete digestive juices to help break down and dissolve the food they want to consume. According to a study, they indeed regurgitate some digestive enzymes that allow them to feed on the liquefied material. However, not all flies display this behavior, and even those that do might not “throw up” on every landing.

It is essential to be cautious and maintain proper sanitation levels, as some flies, like the house fly, can carry pathogens and contaminate food upon contact.

The House Fly: An Overview

The Role of Flies in the Ecosystem

  • House flies (Musca domestica) play a role in breaking down organic matter.
  • They also serve as a food source for predators like birds, frogs, and spiders.

Different Fly Species and Their Habitats

House Flies

  • Found on all continents except Antarctica.
  • Abundant around livestock, poultry, and companion animals.
  • Thrive in feces, garbage, and rotting organic materials. Source
  • They are non-biting, but are considered nuisance and filth flies. Source
  • Adults are gray and black, 6-9 mm long.


  • Found in various environments, particularly near standing water.
  • Female mosquitoes feed on blood to produce eggs.
  • Mosquitoes can transmit dangerous diseases to humans and animals.
  • Adults are slender and long-legged, usually less than 15 mm long.

Comparison between House Flies and Mosquitoes:

Feature House Flies Mosquitoes
Biting No Yes (females)
Disease transmission Rarely Commonly
Size (Adult) 6-9 mm Up to 15 mm
Preferred habitat Livestock, feces, garbage Standing water, damp areas


  • House fly infestations occur when there’s an abundance of breeding sites and resources.
  • Eliminating breeding sources, like garbage or feces, can help reduce fly numbers. Source
  • Infestations are monitored using baited traps, sticky ribbons, or spot cards in livestock facilities. Source

Flies and the Digestive Process

Liquid Diets and Nutrient Absorption

Flies primarily consume a liquid diet due to their unique feeding mechanism. The process begins when a fly lands on food and pushes saliva onto it. The saliva contains enzymes that break down the food into a liquid form for the fly to consume. This allows flies to digest and absorb the proteins and other nutrients from various sources, such as decaying organic matter and sugary substances.

Sample food sources for flies:

  • Decaying fruits
  • Syrup
  • Animal waste

Regurgitating Saliva and Digestive Juices

When flies land on a food source, they regurgitate a mixture of saliva and digestive juices onto the surface. This not only helps to dissolve the food but also facilitates the absorption of nutrients by the fly. While this process benefits the fly, it is less desirable for humans, as the fly’s regurgitation can spread bacteria and cause contamination.

Comparison between flies and humans digestion:

Aspect Flies Humans
Diet Liquid Solid and liquid
Food-processing Regurgitation/saliva Chewing/enzymes
Nutrient uptake External digestion Internal digestion

In conclusion, flies have adapted to their liquid diet through the process of regurgitating saliva and digestive juices to break down and consume nutrients from various food sources. However, this process can lead to contamination and the spread of bacteria, posing potential hazards to human food safety.

Do Flies Poop and Pee When They Land?

Fly Defecation Explained

Flies do indeed poop and pee while they are moving about. They have an anus similar to other animals, allowing them to excrete waste as needed. Here are some quick facts about fly defecation:

  • Frequency: Flies can defecate every few seconds to minutes, depending on their size and diet.
  • Location: They are not picky about where they deposit their waste, often doing so while flying or walking on surfaces.

Uric Acid and Gas Release

When it comes to uric acid and gas release, here’s what you need to know:

  • Uric Acid: Flies excrete uric acid, which is a primary component in their urine. This is a white, crystalline substance that you might notice on surfaces where flies have landed.
  • Gas Release: Flies can also release gases as they digest their food. This is a natural part of their metabolic process.

Comparison Table

Flies Other Insects
Poop Yes Yes
Pee Yes (uric acid) Yes (varies)
Gas Release Yes Yes


  • When a fly lands on your food, there’s a chance it might have pooped or peed on it.
  • Sweeping a fly-infested area could reveal white uric acid deposits on the surface.

Pros and Cons of Fly’s Natural Processes

Pro: Flies naturally break down organic matter, helping with decomposition in ecosystems.

Con: Their indiscriminate defecation and urination contribute to the spread of diseases.

Flies, Germs, and Disease Transmission

Bacterial Contamination of Food

Flies, specifically the common house fly, pose a health risk due to their ability to contaminate food. When flies land on a food source, they may:

  • Deposit germs and bacteria
  • Lay eggs

Examples of bacteria commonly carried by flies include E. coli and Salmonella. These may lead to foodborne illnesses if humans consume contaminated food.

Pathogens and Parasites Carried by Flies

In addition to bacteria, flies may also carry pathogens and parasites. Here’s a comparison of two parasites commonly associated with fly-transmitted diseases:

Parasite Disease Associated Symptoms
Plasmodium spp. Malaria Fever, chills, flu-like illness
Onchocerca volvulus Onchocerciasis (River Blindness) Skin inflammation, vision problems

Flies transmit these diseases as they feed on humans or other animals, transferring pathogens in the process. To minimize health risks, it’s essential to maintain good hygiene and sanitation practices, such as:

  • Regularly clean kitchen surfaces
  • Properly store food items
  • Dispose of waste in a timely manner

Fly Control and Prevention

Insecticides and Repellents

Fly control is crucial as flies are known for spreading diseases by landing on food and contaminating it with their excretions. Insecticides and repellents play a useful role in keeping homes and other environments safe from these pests. For instance:

  • Insecticides: Use products containing Bacillus thuringiensis var. israelensis for effective aquatic fly control source.


  • Effective in reducing fly population


  • Possible negative effects on other organisms in the environment

  • Repellents: Apply natural alternatives like essential oils (e.g., Lavender, Eucalyptus, and Lemongrass) to ward off flies.


  • Safer for human health
  • Environmentally friendly


  • Requires more frequent application
  • May not be as effective as chemical-based insecticides

Keeping a Clean and Healthy Environment

Preventing fly infestations starts with maintaining cleanliness and hygiene standards in your immediate surroundings. Here are some essential tips:

  • Garbage management: Tie plastic bags tightly to reduce odor and use garbage cans with tight-fitting lids. Place them as far away from your home as possible source.

  • Regular cleaning: Clean garbage cans often, remove food residue, and manage odors.

  • Yard maintenance: Remove potential breeding sites like animal manure, rotting mulch, and dead animals from your property.

By incorporating these preventive measures, you can efficiently limit the energy and resources required for fly control while ensuring safer food handling and enhanced hygiene conditions.

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 – Little House Fly


What kind of fly is this?
July 31, 2009
They fly around in circles around each other in the middle of my covered patio. They fly slow and in a position where their rear ends are down much lower than their heads. They are smaller than normal house flies but much larger than fruit flies. They don’t care about fly paper. Nothing seems to get rid of them! What can I do to get rid of them? Thanks!
Lakewood, WA

Little House Fly
Little House Fly

Hi Cheryl,
Your fly is Fannia canicularis, and it is commonly called the Little House Fly.  Here is what Charles Hogue writes about the Little House Fly in his book Insects of the Los Angeles Basin:  “This is the fly you see on hot summer days, in the garage, under trees, in doorways, and in other shaded places, hovering in the air, seeming never to land nor to have a place to go.  this aimless flight immediately distinguishes this species from our other domestic flies, which fly with purposeful direction and frequently come to rest.  Swarms of Little House Flies consist mainly of males;  the females usually remain at rest nearby.  the Little House Fly is 3/16 inch (5 mm) long, smaller that the House Fly, and it  has a slightly more slender body.  At rest its wigs overlap and are held together in parallel fashion.  Although a maggot, the larva is atypical in that it is flat, oval in shape, and possesses numerous branched projections radiating from edges of the body.  Breeding occurs in a wide variety of rotting organic materials.  The larvae in our area show some preference for chicken manure, and the species abounds around poultry ranches.  In urban areas breeding sites are similar to those of the other domestic flies.”  The UC Davis Flies Management Guidelines web page has some good information on this species, and the Exploring California Insects page indicates:  “Larvae breed in filth and are attracted by the smell of human urine.”
P.S.  We will not be tagging your entry as Unnecessary Carnage, as we really don’t consider every insect that dies by human hands to warrant that distinction.

Letter 2 – Humpbacked Flies


Subject: What kind of fly is this?
Location: Illinois
October 29, 2012 4:34 pm
These are flying all around in our my apartment buildings hallway. They have been following me in and I now have them flying around my apartment. They don’t seem to fly a lot though. They tend to land and then dart around really fast. This has made them fairly easy to kill. I have never seen flies like these before and am not seeing them online anywhere. I have noticed that when I kill one a very small reddish orange bug comes off of it. The last one I killed had two of these tiny bugs crawl out or off of it. I have had a hard time getting a good pic of these but I have attached the best one I have. Any info you have would be much appreciated as I am so sick of dealing with these things.
Signature: J Crellin

Humpbacked Flies

Dear J Crellin,
We will be checking with Eric Eaton for assistance on this identification.

Eric Eaton assists in Humpbacked Flies identification
Yes, Daniel, those are humpbacked flies, family Phoridae.  Probably Megaselia scalaris, by far the most abundant indoor species.  They feed on decaying matter as larvae, so you find them mostly in the kitchen, around the garbage disposal, etc.

Letter 3 – Invasion Of Flies!


My boyfriend and I recently returned from a week long vacation. When we came home we began noticing giant black houseflies everywhere.
The are huge, and it seems like every time we get rid of one, another 3 appear out of nowhere. What the heck is going on here? They are really freaking me out. What can I do bout them?
Jackie Rosenthal

Dear Jackie,
You (or your boyfriend) must have left some organic matter, probably in the garbage can, and a single female fly laid her eggs. If it was warm, they matured quickly. There is not much you can do about the current brood but swat them. Just make sure there is nothing rotting in the house to provide food for a future generation.

Letter 4 – Just What We Need: More Houseflies!!!


Marian, a frequent contributor from Florida sent in this photo of Musca domestica, the Housefly, doing it. Guess there will be maggots on the way soon.

Letter 5 – Mating Flies


Buzz Buzz
Hello Again!
Love the site! Took this picture of a mantis that’s been around for a while and was wondering if you guys could tell me what’s happening. Is she about to lay some eggs? Is she dying? Also, inspired by all the ‘intimate’ moments I see posted, I have sent a picture I just took of two flies in the throes…

Hi Dina,
Your mantis photo is too blurry to post, but she does look like she is going to lay eggs. Hopefully she isn’t egg bound. Love the mating fly photo.


  • 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: Flies

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