Blow Fly: All You Need to Know for Effective Pest Control

Blow flies are fascinating insects often found around dead animals, playing a unique role in the decomposition process.

These flies, known for their metallic blue or green color, are part of nature’s cleanup crew and help break down organic materials.

Despite their somewhat unsettling associations, blow flies do not pose any direct threat to humans.

The life cycle of a blow fly is an intriguing aspect of these insects. From eggs to adults, each stage serves a purpose in the overall growth and development of the blow fly population.

Understanding this cycle can help us appreciate their role in the ecosystem and even assist forensic investigators in determining time of death in certain cases.

Some flowers have evolved to exploit the blow fly’s affinity for dead animals, evolving to mimic the appearance and smell of rotting flesh to attract these insects for pollination.

This unique relationship between flies and flowers is an example of the diverse ways in which different organisms interact within their environments.

Overview and Characteristics of Blow Flies

Physical Appearance

Blow flies are known for their distinct colors such as blue, green, and black. They often have a shiny, metallic green appearance, making them easily recognizable.

These flies are typically bigger than house flies. Here is a summary of some of key features of their appearance:

  • Metallic colors (green, blue, black)
  • Shiny green or greenish-blue tones
  • Larger than house flies
  • Hairlike bristles

Behavior and Habits

Blow flies exhibit specific behaviors and habits that are unique to their species.

For example, they are attracted to decaying organic matter and often lay their eggs in deceased animals.

The larvae (maggots) infest the carcass for 5-10 days before leaving in search of a dry place to pupate.

Comparison between blow flies and normal house flies

Blow Flies House Flies
Metallic, shiny green color Duller, gray color
Bigger in size Smaller in size
Feed on decaying organic matter Feed on a variety of food sources

Global Distribution

Blow flies have a widespread global distribution, thriving in diverse habitats from tropical to temperate regions.

For instance, the southern hemisphere, particularly Australia and parts of South America, witnesses a higher incidence of blow fly-related veterinary issues due to the predominant species in those regions.

They are especially prevalent in warm, humid areas, which provide ideal conditions for their life cycle.

Different species have adapted to various regions, with some preferring forested environments and others urban areas.

While they are found on every continent, their density and species variety might differ.

Blow Fly Life Cycle

Eggs and Larvae

Blow flies begin their life cycle as eggs, which are laid by adult female flies on recently deceased animals or open wounds1.

Within 24 hours, the eggs hatch into first-stage maggots2.

These maggots feast on the carcass, then molt into second-stage maggots, which continue feeding2.

First-stage maggots:

  • Hatch within 24 hours of egg-laying2
  • Feed on carcasses before molting2

Second-stage maggots:

  • Result of molting first-stage maggots2
  • Continue feeding on carcasses2

Pupa Stage

After 5-10 days of feeding, the larvae leave the carcass to find a dry location, where they pupate3.

They remain in the pupa stage until they’re ready to emerge as adult blow flies3.

Pupa stage features:

  • Lasts until adult emergence3
  • Occurs in a dry location3

Adult Stage

Once they’ve completed the pupa stage, blow flies emerge as adults3.

Adult blow flies have a checkerboard-patterned abdomen, distinguishing them from other species.

Adults lay eggs on or near suitable habitats, and the life cycle begins anew4.

Adult blow fly characteristics:

  • Emerge after pupa stage3
  • Lay eggs on or near suitable habitats4
  • Checkerboard-patterned abdomen4

Comparison Table

Stage Duration Key Features
Eggs 24 hours Laid on carcasses or open wounds1, hatch into maggots2
Larvae 5-10 days Feed on carcasses, molt into second-stage maggots2
Pupa Varies Occurs in dry locations, lasts until adult emergence3
Adult Varies Lay eggs, have checkerboard-patterned abdomen4

Blow Flies in Homes and Their Impact on Humans

Infestation Causes

Blow flies, also known as bottle flies, are attracted to decaying organic matter, garbage, and animal waste. Causes of infestations in homes include:

Potential Risks and Diseases

Blow flies, while essential decomposers, can pose medical and veterinary challenges.

In humans, certain species can cause myiasis, a condition where fly larvae infest living tissue, leading to painful lesions.

In livestock, blow fly infestations, often termed “flystrike,” can be detrimental. Animals with open wounds or uncleaned afterbirth residues are particularly vulnerable.

File:Close-up of Chrysomya (Old World blow fly) on a green leaf.jpg
Source: Basile Morin, CC BY-SA 4.0, via Wikimedia Commons

The larvae feed on the tissue, causing distress, secondary infections, and in severe cases, death. Early detection and treatment are crucial to manage these conditions.

Other risks associated with blow flies include:

  • Contamination of food: Fly contact with human food can transmit bacteria and diseases such as E.coli and Salmonella.
  • Indication of a dead animal: If an infestation occurs, it might be due to an animal carcass in the vicinity, which could pose health risks if left undiscovered.

Preventing and Controlling a Blow Fly Infestation

Taking steps to prevent and eliminate blow flies from homes can minimize risks and maintain a clean living environment.

Strategies to manage infestations include:

  • Secure waste disposal: Properly cover garbage cans and compost piles to limit access for blow flies seeking a breeding ground.
  • Remove potential breeding sites: Inspect your home for dead animals, such as rodents or birds, and remove them promptly.
  • Install screens on windows and doors: Installing screens can prevent blow flies from entering your home.
  • Use insecticides and fly traps: Specific indoor insecticides labeled for fly control can be used to eliminate adult flies. Fly traps are an additional method of control.

By addressing the sources of blow fly infestations and taking preventive measures, you can minimize the impact these pests have on your home and health.

Control and Management

Managing blow fly populations is essential, especially in areas prone to infestations.

Non-chemical methods include regular sanitation, prompt removal of dead animals, and wound management in livestock.

Fly traps and screens can reduce their intrusion into homes.

Chemical control, like insecticides, can be effective but should be used judiciously to prevent harm to beneficial insects and the environment.

Biological control, using natural predators or pathogens, offers an environmentally friendly alternative.

Regardless of the method, an integrated approach combining multiple strategies often yields the best results.

File:Calliphoridae - Blow Fly.jpg
Karz09, CC BY-SA 4.0 <>, via Wikimedia Commons

Blow Flies and Decomposition

Role in Nature and Ecosystems

Blow flies play a vital role in decomposing dead animals, such as carrion or recently deceased animals.

Their larvae, also known as maggots, feed on the dead or decaying organic matter.

This decomposition process supports plant growth and maintains soil health.

Moreover, blow flies serve as a food source for various predators, including birds, reptiles, and other insects.

Their presence, therefore, is an indicator of a balanced ecosystem, signifying the health and diversity of an environment.

Forensic Entomology

Blow flies play an essential role in forensic entomology, where their development stages help determine the post-mortem interval (PMI) or time since death.

For example, on decomposing human bodies, if temperatures around a body are moderate, investigators can gauge the development stages of blow fly larvae to estimate the time elapsed since death.

Here’s a comparison of blow flies and some close relatives, bottle flies:

Feature Blow Flies Bottle Flies
Preferred food source Dead or decaying organic matter Same as blow flies
Life cycle duration 3 to 4 weeks Similar to blow flies
Role in decomposition Important in recycling nutrients Similar to blow flies
Forensic application Used to determine PMI Not as commonly used as blow flies

It is essential to recognize blow flies’ ecological significance and forensic applications while managing their populations to keep them under control in homes and farms.


Blow flies, with their distinctive metallic hue, play a crucial role in nature’s decomposition process, aiding in the breakdown of organic materials.

Their life cycle, from eggs to adults, offers insights into their development and ecological significance.

While they can be a nuisance in homes due to their attraction to decaying matter, their importance in forensic investigations and their symbiotic relationship with certain flowers showcase their multifaceted role in the ecosystem.


  1. Life cycle of the black blow fly – National Library of Medicine 2
  2. PDF Blow Fly Life Cycle – National Library of Medicine 2 3 4 5 6 7 8
  3. Blow and Flesh Flies | Horticulture and Home Pest News 2 3 4 5 6 7
  4. Blow Fly – Texas A&M University 2 3 4

Reader Emails

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

Letter 1 – Cluster Flies appearing in home

Large Black Flies
March 26, 2010
For the second time in about five years, we have large black flies in our house. They are not coming in from the outside and they seem to spend most of their time on our windows.

In two days, I have swatted at least 50-60, so you can imagine how gross this problem is. We do have cracks where the windows meet walls-our house is on a slab, but it shifts considerably. We have not noticed any foul odors, except under the kitchen sink, but there is not a leak or sign of anything that may have died under there. We do keep rat poison in the attic, but my husband checked and found no sign of anything that died up there.

I’m concerned about the health risk and have no idea, other than swatting, how to get rid of them or where they come from. Please, I hope you can help. I’d li ke to know if they bite, spread disease and how long they live, besides how to get rid of them. (I saw Amityville Horror and already told my husband that if the walls begin to bleed, I’m outta here! LOL!)Thanks-Linda
Linda Mendez
Houston Texas

Cluster Flies

Hi Linda,
It is difficult to make out any details in your images, but your description is consistent with an outbreak of Blow Flies.  Many of the Blow Flies pictured on BugGuide have metallic coloration in shades of green and blue, but others are black like your specimens. 

It is possible that the poison dispatched a rat and a female Blow Fly was attracted to the rotting flesh where she laid her eggs.  We will check with Eric Eaton to see if he concurs.  If blood begins to seep from the walls, please let us know.

Cluster Fly

Eric Eaton Agrees
Yes, I would bet on blow flies, probably “cluster flies” in the genus Pollenia.  Cluster flies are well known for harboring between walls during the colder months, then emerging in vast numbers as described in the letter.  Still, I’d have to examine actual specimens before I could be certain.

Wow, thanks so much for the speedy reply-I’ll go to your website for answers on health and getting rid of them. Some of these do have the coloration you mentioned. I appreciate your help-Linda

Letter 2 – Blow Fly

Geographic location of the bug:  My school in North America, sand box by the swings
Date: 11/02/2017
Time: 11:02 PM EDT
There are green flying bugs at my school’s sandbox. Whenever I go to get on one of the swings in the sand box, I get scared because kids tell me that the bugs are sand bees. I looked them up, no results besides sand wasps, which do not look like the bugs I saw.

They bugs burrowed into the sand, and dug holes in it. They appeared to be a spring grass green and they kind of hovered over the ground a little like a bee. I can not get a close look at one, Im too scared, but I just avoid them whenever I can.

I would just like to know what type of bug it is, and if you can not figure that out, see if you can tell me if I should avoid them/report them to the school. Thank you! (both images attached are what the bee-thing kind of looked like, a mix between the two)
How you want your letter signed:  Cassie

Blow Fly

Dear Cassie,
The image you provided is of a Blow Fly in the family Calliphoridae which you can verify by comparing it to this BugGuide image. 

According to BugGuide, they are:  “scavengers (larvae in carrion, excrement, etc.) or parasites” which might mean animals (or children) are using the sandbox for some unsanitary purposes, or that there is something dead buried in the sandbox. 

BugGuide also indicates:  “Commonly seen ‘basking’ on the exterior walls of buildings (flesh flies also have this habit). Some cause myasis in humans and livestock.”


  • 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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5 thoughts on “Blow Fly: All You Need to Know for Effective Pest Control”

  1. Oh my goodness. I have killed 3 big flies. I came here from searching this problem up on google. I am terrified of flies. My room is pretty clean beside some dust here and there. As I am typing this, there is a fly sitting in the corner of my window right now.

  2. We bought our home three year ago, (20 year old home in Georgia). One day when spring was starting, we noticed large, black flies on the windows and ceiling. They are slow and lethargic so it was easy to use a vacuum cleaner and eventually get them. We have been diligent in sealing up everything we can find where they might have been hiding during the winter. Now in our third year, this spring I found and killed less than 20, compared to hundreds during the first year. We hope that we have seen the last of them. Local pest companies didn’t really know what to do about it. Just tackle the problem, and eventually you will get control of it.

  3. The picture is indeed a fly.

    However, I strongly suspect that a misidentification was made by the worried poster. Digging holes in sand and hovering does not sound like typical blowfly behavior.

    I think that the insects might indeed be sand-loving hymenopterans, but they should be very peaceful and ignore humans, even if annoyed. However, it MIGHT be possible (don’t jump to conclusions and reach for the exterminator) that schoolchildren determined to kill or torture the poor insects will suffer retaliation, so I am slightly concerned.

  4. The picture is indeed a fly.

    However, I strongly suspect that a misidentification was made by the worried poster. Digging holes in sand and hovering does not sound like typical blowfly behavior.

    I think that the insects might indeed be sand-loving hymenopterans, but they should be very peaceful and ignore humans, even if annoyed. However, it MIGHT be possible (don’t jump to conclusions and reach for the exterminator) that schoolchildren determined to kill or torture the poor insects will suffer retaliation, so I am slightly concerned.


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