Blow Fly (Calliphoridae) – Identification, Life Cycle and Control

Blow flies (family Calliphoridae) are a group of flies commonly found throughout the United Kingdom. Familiar examples include the bluebottle fly (Calliphora vicina) and common greenbottle fly (Lucilia sericata). Many species are recognised by their metallic blue, green or bronze colouring, robust bodies and noticeable buzzing flight.

Blow flies play an important role in nature by helping break down dead animals and other decomposing organic matter. However, they can become a nuisance when they enter homes, develop in waste or breed in concealed areas of buildings. Their ability to locate suitable breeding material quickly means a large number of flies can sometimes appear over a relatively short period.

In UK properties, sudden blow fly activity may be associated with a dead rodent or bird in a loft, chimney or wall cavity. Adult flies may gather around windows after emerging from a hidden breeding source, while their larvae, commonly called maggots, may be found around refuse bins or other areas containing decomposing material.

Blow flies are also relevant to food hygiene because they can move between waste, animal remains and food preparation surfaces. Although finding an occasional fly indoors does not necessarily indicate an infestation, persistent activity should be investigated to establish where the insects are coming from.

This species profile explains how to identify blow flies, distinguish them from other common flies, understand their life cycle and recognise signs of an infestation. It also covers their ecological importance, potential hygiene concerns and the measures used to manage blow fly problems in homes and businesses.

Blow Fly – Quick Facts

Blow Fly Taxonomy and Classification

Blow flies belong to the family Calliphoridae within the order Diptera, which contains the true flies. Unlike the name of an individual species, the term blow fly refers to a group of related insects that share certain physical and biological characteristics.

Different blow fly species vary in their appearance, preferred breeding material, seasonal activity and development rates. These differences can be important when investigating an infestation.

How to Identify a Blow Fly

Many blow flies can be recognised by their relatively large bodies and distinctive metallic colouring. However, identification should consider several features because not every species has the same appearance.

Adult Body Size

Adult blow flies commonly measure approximately 6–14 mm in length. They often appear larger and more robust than ordinary house flies, although size overlaps between different fly groups.

Metallic Colouring

Many familiar blow flies have metallic blue, green or bronze colouring across the thorax or abdomen.

Bluebottles are particularly recognisable by their metallic blue appearance, while greenbottles commonly display bright green colouring. Some blow fly species are less conspicuously metallic.

Eyes

Blow flies have large compound eyes that help them detect movement and navigate their surroundings. Eye colour and spacing vary between species and sexes.

Wings

Like other true flies, blow flies have one functional pair of wings. Their wings are generally transparent with visible veins.

Behind the wings are small balancing organs called halteres, which help stabilise the insect during flight.

Antennae

Blow flies possess relatively short antennae with a bristle-like structure known as an arista. Their sensory systems help them locate food and suitable breeding material.

Mouthparts

Adult blow flies have mouthparts adapted primarily for taking up liquids. They may feed on accessible fluids associated with decomposing material and other suitable food sources.

Blow Fly Larvae

Blow fly larvae are commonly called maggots. They are usually cream-coloured or whitish, legless and elongated, with a tapered front end.

Larvae develop in suitable organic material and can grow rapidly when temperatures and food availability are favourable.

Common Types of Blow Flies in the UK

Bluebottle Fly (Calliphora vicina)

The bluebottle fly is one of the most familiar blow flies encountered in Britain. It has a robust body with metallic blue colouring and is commonly associated with animal remains and other suitable decomposing material.

Bluebottles may enter homes and gather around windows, particularly when adults emerge from a concealed breeding source.

Common Greenbottle Fly (Lucilia sericata)

The common greenbottle has a distinctive metallic green body. It is associated with decomposing organic matter and is also important in veterinary contexts because its larvae can cause flystrike in susceptible animals.

Adult greenbottles may be encountered in gardens, around waste storage areas and in other outdoor environments.

Other Blow Fly Species

Several additional species within the Calliphoridae family occur in Britain. Their colour, size and breeding preferences can vary, and accurate species-level identification may require specialist examination.

Blow Flies vs House Flies and Cluster Flies

Blow flies can be confused with other flies commonly found inside buildings. Distinguishing between them is important because their breeding habits and the reasons for their appearance may differ.

Large numbers of flies gathering at windows do not automatically indicate blow flies. Cluster flies may display similar behaviour, particularly when emerging from sheltered areas of buildings.

Where Do Blow Flies Live?

Blow flies occur in a wide range of urban, suburban and rural environments. Adults can travel between feeding and breeding locations, while larvae require suitable material in which to develop.

Gardens and Outdoor Areas

Adult blow flies may be found around vegetation, gardens and outdoor spaces where suitable food or breeding material is available.

Refuse Bins

Bins containing exposed food waste or animal-derived refuse can attract egg-laying females. Moist organic material may provide suitable conditions for larval development.

Lofts and Roof Spaces

A dead bird or rodent in a loft can provide breeding material for blow flies. Emerging adults may later enter occupied rooms through gaps or other openings.

Wall Cavities

Animal remains within wall cavities or structural voids can support larval development. The source may remain hidden even after adult flies become noticeable.

Chimneys

Dead birds or other animal remains in chimney structures can sometimes attract blow flies and support their development.

Commercial Waste Areas

Refuse storage and waste handling areas may attract blow flies when suitable organic material remains accessible.

Food-Related Premises

Food preparation and storage environments may experience blow fly activity when adults enter from outside or suitable breeding sources are present nearby.

Are Blow Flies Common in the UK?

Yes. Blow flies are widespread throughout Britain and are particularly noticeable during warmer periods of the year.

Different species have different seasonal activity patterns and temperature preferences. Some remain active in relatively cool conditions, while others become more noticeable during warmer weather.

Blow flies occur throughout Greater Manchester, Cheshire and Merseyside, as well as other parts of the UK.

Their presence outdoors is normal. However, repeated indoor activity, particularly when accompanied by maggots or unusual odours, may indicate a source that requires investigation.

What Do Blow Flies Eat?

Adult blow flies and their larvae use different food sources and feeding methods.

Adult Blow Flies

Adults may feed on liquids associated with decomposing organic material, animal waste and other suitable substances. Some species also visit flowers and consume nectar.

Blow Fly Maggots

Larvae commonly feed within moist, decomposing animal material or other suitable organic matter. Their feeding contributes to the breakdown of the material.

Animal Remains

Dead rodents, birds and other animals can provide suitable breeding material for certain blow fly species.

Food Waste

Accessible waste containing suitable moist organic material may attract adult flies and support larval development.

Living Animal Tissue

Certain blow fly species can develop in living tissue, causing a condition known as myiasis. This is particularly important in veterinary settings.

Blow Fly Life Cycle and Reproduction

Blow flies undergo complete metamorphosis, developing through four stages: egg, larva, pupa and adult.

The speed of development depends on the species, temperature and suitability of the breeding material.

1. Egg Stage

Female blow flies lay eggs on suitable breeding material. Depending on the species and circumstances, a batch may contain approximately 100–200 eggs.

Under favourable warm conditions, eggs may hatch within approximately 8–24 hours, although cooler temperatures can extend this period.

2. Larval Stage

After hatching, the larvae begin feeding on the surrounding material.

They pass through three larval stages, known as instars, as they grow.

In warm conditions, larval development may take only several days. Cooler conditions generally slow their growth.

3. Pupal Stage

Once fully developed, larvae commonly leave the feeding material and move to a protected location to pupate.

They may be found in soil, cracks or other sheltered areas near the original breeding source.

The outer larval skin hardens to form a protective puparium, inside which the adult develops.

4. Adult Stage

After development is complete, the adult fly emerges.

Adults may then disperse in search of food, mates and suitable breeding material.

Where conditions remain favourable, further generations can develop.

Blow Fly Life Cycle Summary

Under favourable warm conditions, some blow fly species can complete development from egg to adult in approximately two to three weeks.

However, this is not a fixed timetable. Development can take considerably longer at lower temperatures.

How Quickly Do Blow Flies Reproduce?

Blow flies can reproduce rapidly when suitable breeding material is available.

Females may lay substantial numbers of eggs, and larval development can be fast during warm weather.

As a result, a concealed carcass or suitable waste source may produce a noticeable emergence of adult flies within a relatively short period.

The sudden appearance of numerous adults does not necessarily mean the flies have been breeding throughout the property. They may have developed from a single localised source.

When Are Blow Flies Most Active?

Spring

Activity generally increases as temperatures rise and suitable breeding material becomes available.

Summer

Warm conditions can support rapid development and increased adult activity.

Autumn

Adults may remain active during mild conditions, although development generally slows as temperatures fall.

Winter

Some blow fly species can survive colder periods in protected environments or through particular developmental stages.

Indoor heating and sheltered breeding sources may also influence activity during colder months.

Why Do Blow Flies Suddenly Appear in a House?

A sudden appearance of several large flies indoors can be unsettling, particularly when doors and windows have remained closed.

There are several possible explanations.

A Dead Rodent

A rat or mouse that has died in a concealed area may provide suitable breeding material. Adult flies can emerge after the larvae complete their development.

A Dead Bird

Animal remains in roof spaces, chimneys or other sheltered areas may attract blow flies.

Accessible Food Waste

Waste containing suitable organic material may support breeding, particularly during warmer conditions.

An Overlooked Breeding Source

Organic material behind appliances, in outbuildings or within concealed spaces may be responsible.

Flies Entering from Outside

Not every blow fly found indoors has developed inside the property. Adults may enter through open doors, windows or other openings.

Repeated emergence from one area, particularly over a short period, makes a local breeding source more likely.

Why Are Blow Flies Gathering at Windows?

Adult blow flies may move towards daylight after emerging inside a building.

This can result in several flies collecting around windows or glazed doors.

Window activity alone does not confirm where the insects developed. However, repeated appearances near the same room, particularly alongside an unusual odour, may justify investigating nearby voids or other concealed areas.

What Are the Signs of a Blow Fly Infestation?

Blow fly activity is often obvious once adult numbers increase, but the original breeding source may remain hidden.

• Large flies indoors: Repeated sightings of metallic blue, green or dark flies.
• Flies at windows: Adults gathering around natural light.
• Maggots: Pale larvae moving away from waste or breeding material.
• Unusual odours: A smell associated with decomposing organic matter.
• Activity near bins: Flies repeatedly visiting refuse storage areas.
• Empty puparia: Small brownish cases remaining after adult emergence.
• Sudden emergence: Numerous flies appearing over a short period.
• Recurring activity: Further flies appearing despite the removal of visible adults.

These signs should be assessed together rather than used individually to identify the cause.

Do Blow Flies Bite or Sting?

Common household blow flies such as bluebottles and greenbottles do not possess a sting and are not adapted to biting people in the manner of blood-feeding flies.

Their main significance indoors is associated with nuisance activity, contamination and suitable breeding sources.

Are Blow Flies Dangerous?

Blow flies can create hygiene concerns because they may move between decomposing material and surfaces used by people.

Food Contamination

Flies that contact waste or animal remains may subsequently land on exposed food, creating opportunities for microorganisms to be transferred.

Food Preparation Surfaces

Persistent fly activity in kitchens and commercial food areas can interfere with hygiene standards.

Mechanical Transfer of Bacteria

Blow flies may carry microorganisms on their bodies or through contact with contaminated materials.

Potentially relevant bacteria include Salmonella and Escherichia coli, although the presence of a fly does not establish that either organism is present.

Myiasis

Certain blow fly species can cause myiasis when larvae develop in living tissue.

This is particularly important in veterinary settings, where flystrike can affect susceptible animals.

Human myiasis is uncommon in the UK and should not be treated as a typical consequence of ordinary household blow fly activity.

Nuisance and Disturbance

Large, noisy flies can be particularly unpleasant in kitchens, bedrooms and occupied commercial spaces.

What Is Flystrike?

Flystrike is a form of myiasis in which fly larvae develop on an animal.

Some blow fly species, including the common greenbottle, are important causes of flystrike in sheep and other susceptible animals.

Flies may be attracted to soiled fleece, wounds or other suitable conditions.

Flystrike can develop rapidly and requires prompt veterinary attention.

It is a separate issue from the typical indoor blow fly infestations encountered in homes.

Can Blow Flies Damage Property?

Blow flies do not normally damage timber, wiring or structural building materials.

Their impact is primarily associated with hygiene, contamination and the nuisance caused by adult flies and larvae.

Food and Stored Products

Exposed food may become unsuitable for consumption after contact with flies or breeding material.

Refuse Areas

Larval development in waste can create unpleasant conditions and require additional cleaning.

Concealed Animal Remains

A carcass in a building may produce odours and support fly development. The underlying animal remains, rather than the flies themselves, are often the main issue requiring attention.

Commercial Environments

Visible fly activity can result in customer complaints, product concerns and additional cleaning requirements.

Why Do Blow Flies Keep Coming Back?

Repeated blow fly activity usually indicates that adults continue entering the property or that suitable breeding material remains available.

The Breeding Source Remains

Removing adult flies does not eliminate eggs, larvae or pupae already developing nearby.

Concealed Animal Remains

A dead rodent or bird may remain hidden within a building void.

Waste Is Still Accessible

Bins or other waste storage areas may continue attracting adult flies.

Adults Continue Entering

Openings around doors, windows and other building features may allow flies to enter from outside.

Misidentification

Cluster flies and other fly species may be mistaken for blow flies, leading to an incorrect assessment of the problem.

How to Get Rid of Blow Flies

Effective blow fly management focuses on identifying and addressing the source rather than only removing adult insects.

1. Identify the Fly

Establish whether the insects are blow flies, house flies, cluster flies or another group.

Identification helps determine likely breeding locations.

2. Investigate the Source

Look for accessible waste, decomposing material and evidence of dead animals.

Where activity is concentrated around a particular room or structural void, a targeted inspection may be appropriate.

3. Remove Accessible Breeding Material

Where safe and practical, remove suitable organic waste or animal remains.

Any removal should account for hygiene risks and safe handling requirements.

4. Clean Affected Areas

Clean accessible surfaces and waste storage areas using suitable methods.

Dispose of contaminated materials appropriately.

5. Reduce Fly Entry

Check doors, windows, screens and other accessible openings.

Suitable exclusion measures can help reduce entry from outside.

6. Consider Targeted Treatment

Where necessary, professional treatment may help manage remaining fly activity.

Any insecticide should be authorised for its intended use and applied according to the product label.

Treatment alone may not resolve the problem if the breeding material remains.

How to Prevent Blow Fly Infestations

Prevention focuses on waste management, hygiene and reducing opportunities for flies to enter buildings.

• Keep refuse bins closed where practical.
• Remove food waste regularly.
• Clean bins when residues accumulate.
• Keep exposed food covered.
• Inspect waste storage areas for signs of larvae.
• Use suitable fly screens where appropriate.
• Maintain accessible seals around doors and windows.
• Investigate persistent odours or unexplained fly activity.
• Address known animal problems that may contribute to concealed carcasses.
• Monitor recurring activity after cleaning or treatment.

Good hygiene can reduce attractive conditions, but it may not prevent flies from entering from neighbouring outdoor sources.

Why Are Blow Flies Important in Nature?

Blow flies play an important role in the decomposition of dead animals and other organic material.

Decomposition

Larval feeding helps break down suitable organic material and return nutrients to the environment.

Food for Other Animals

Blow flies and their larvae provide food for birds, spiders, predatory beetles and other animals.

Forensic Entomology

Blow fly development is important in forensic science.

Investigators can examine the species present and their developmental stages, alongside temperature and other environmental evidence, to help estimate the minimum time since insect colonisation of remains.

For more information about the scientific importance of blow flies, see the Natural History Museum’s explanation of blow flies and forensic entomology.

Developmental estimates require specialist interpretation because temperature, access to remains and other conditions can significantly affect the insects’ growth.

Professional Blow Fly Control

Persistent blow fly activity can be difficult to resolve when the breeding source is concealed or inaccessible.

Youngs Pest Control provides professional fly control services for domestic and commercial properties throughout Greater Manchester, Cheshire and Merseyside.

Our approach focuses on identifying the type of fly, investigating the likely source and selecting suitable measures for the property.

1. Inspection and Assessment

We inspect affected areas to establish the extent of fly activity and investigate likely breeding sources.

This may include accessible lofts, waste storage areas, kitchens, outbuildings and other relevant locations.

2. Fly Identification and Source Investigation

We assess the type of fly involved and investigate whether the activity is associated with waste, animal remains or another source.

Correct identification is particularly important where blow flies are being confused with cluster flies.

3. Targeted Treatment

Where appropriate, we recommend measures suited to the source and conditions found during the inspection.

This may involve hygiene advice, source removal where safely accessible, exclusion measures or suitable targeted fly treatments.

4. Follow-Up and Prevention Advice

We provide practical guidance on waste management, reducing entry opportunities and monitoring for further activity.

Additional investigation may be necessary where the original source cannot be safely accessed.

Our services are available across the North West. Find out more about our pest control services in Manchester, pest control services in Cheshire and pest control services in Merseyside.

Blow Flies in Commercial Properties

Blow flies can cause disruption in businesses where hygiene, food handling and customer confidence are important.

Restaurants and Cafés

Flies entering food preparation or dining areas can create hygiene concerns and customer complaints.

Food Production Facilities

Suitable waste handling, exclusion and monitoring are important where exposed food or ingredients are present.

Warehouses

Waste accumulation and overlooked organic material may attract flies to storage environments.

Hotels and Hospitality Premises

Large flies appearing in guest rooms or communal areas can create disruption and require investigation.

Waste Management Areas

Refuse storage and handling locations can provide attractive conditions when suitable organic material remains accessible.

Commercial fly management should focus on the source, hygiene, entry prevention and appropriate monitoring rather than relying exclusively on adult fly treatments.

Frequently Asked Questions About Blow Flies

What is a blow fly?

A blow fly is a fly belonging to the family Calliphoridae. Common UK examples include bluebottles and greenbottles.

Are blow flies common in the UK?

Yes. Blow flies are widespread in Britain and are particularly noticeable during warmer months.

What does a blow fly look like?

Many species have robust bodies with metallic blue, green or bronze colouring and clear wings.

Are bluebottles blow flies?

Yes. Bluebottles are members of the blow fly family.

Are greenbottles blow flies?

Yes. Greenbottles, including Lucilia sericata, belong to the Calliphoridae family.

What is the difference between a blow fly and a house fly?

Many blow flies are larger and more metallic in appearance, while house flies are generally dull grey with darker thoracic stripes.

Why are blow flies appearing in my house?

They may be entering from outside or emerging from suitable breeding material such as waste or concealed animal remains.

Do blow flies mean there is a dead rat?

Not necessarily. A dead rodent is one possible source, but flies may also be attracted to other animal remains or suitable organic waste.

Can blow flies breed in lofts?

They may develop in a loft if suitable breeding material, such as a dead animal, is present.

Why are blow flies gathering at windows?

Adults may move towards daylight after emerging indoors, causing them to collect around windows.

What are blow fly maggots?

They are the larval stage of blow flies and commonly develop in moist, decomposing organic material.

How long does the blow fly life cycle take?

Some species can develop from egg to adult in approximately two to three weeks under favourable warm conditions, but timing varies.

Do blow flies bite?

Common household blow flies such as bluebottles and greenbottles are not adapted to biting people.

Do blow flies sting?

No. Blow flies do not possess a sting.

Are blow flies dangerous?

They can create hygiene concerns because they may contact decomposing material and subsequently land on food or preparation surfaces.

Can blow flies spread bacteria?

They may mechanically transfer microorganisms between contaminated material and other surfaces.

What attracts blow flies?

Suitable decomposing animal material, organic waste and other breeding sources can attract them.

Why do blow flies keep returning?

Repeated activity may indicate that breeding material remains present or that adult flies continue entering from outside.

Will fly spray get rid of blow flies?

A suitable product may reduce adult activity, but it will not necessarily resolve the problem if larvae are developing in a concealed source.

How do I prevent blow flies?

Manage food waste, keep bins clean, reduce entry opportunities and investigate persistent activity or unusual odours.

Can blow flies cause flystrike?

Certain species can cause flystrike in susceptible animals. Suspected flystrike requires prompt veterinary attention.

When should I call a pest control professional?

Professional assessment may be useful when large numbers of flies appear suddenly, maggots are found indoors or the breeding source cannot be located.

Blow Fly Identification and Control – Youngs Pest Control

Blow flies are a natural part of the environment, but persistent indoor activity can indicate a problem involving waste, concealed animal remains or other suitable breeding material.

Identifying the fly and locating its breeding source are important steps towards resolving the infestation and reducing the likelihood of recurrence.

Youngs Pest Control is a family-run pest management company with over 35 years of experience and membership of the National Pest Technicians Association.

We provide professional pest inspections, fly control and practical prevention advice for domestic and commercial customers throughout Greater Manchester, Cheshire and Merseyside.

Visit our areas we cover page to find out more about our local pest control services.

If you are experiencing persistent blow fly activity, maggots or suspect a concealed breeding source, contact our team for advice.

Contact Youngs Pest Control:

0161 776 9832

07845 815 261