House fly
House flies are grey rather than strongly metallic blue or green.
FLY IDENTIFICATION
Blow & Bottle Flies
Calliphoridae
Blow flies and bottle flies are medium to large flies, often metallic blue, green or copper. A sudden burst of adults indoors can indicate a dead animal hidden in a wall, attic, chimney or ceiling void, although garbage and other decaying organic material can also support them.
QUICK FACTS
Identification at a glance
FamilyCalliphoridae
Typical sizeAbout 6–12 mm
ColourMetallic blue, green, black or copper
Larval foodCarrion and decaying organic matter
Indoor clueSudden emergence can indicate a carcass
BitingAdults do not normally bite people
OVERVIEW
What property owners should know
Blow flies are among the most visually distinctive structural flies because many species have a shiny metallic body. Their biology is strongly linked to animal remains, meat waste, excrement and other rapidly decomposing organic material.
A few adults entering through a door or window may mean very little. A large synchronized emergence indoors is different: it often means larvae developed on a hidden carcass and adults are now dispersing toward windows and light.
Because larvae may crawl away from the feeding source before pupating, adult flies can emerge some distance from the actual carcass. Inspection should follow the distribution of flies, odour and building voids rather than assuming the source is directly beneath the window where adults collect.
IDENTIFICATION
What to look for
01
House-fly-like body but often larger and more robust
02
Metallic blue, green, bronze or copper sheen on the abdomen or thorax
03
Strong, direct flight compared with tiny drain or fruit flies
04
Adults frequently gather at bright windows after emerging indoors
LIFE CYCLE & BIOLOGY
How the population develops
Females lay eggs on suitable decaying animal material, meat waste, excrement or other protein-rich organic sources.
Larvae develop rapidly in warm conditions, then often move away from the feeding material to pupate in a drier protected location.
University extension guidance notes that a complete life cycle can occur in roughly 10–25 days depending on species and conditions.
HABITAT & HARBOURAGE
Where activity develops
- Dead rodents or birds in wall and ceiling voids
- Chimneys and attics
- Garbage containing meat waste
- Animal waste and contaminated pet areas
- Commercial waste rooms and compactors
- Exterior carrion near doors or ventilation openings
Seasonality
Blow flies are most active outdoors in warm weather, but hidden indoor carcasses can produce adult emergence whenever temperatures support development.
VISIBLE EVIDENCE
Signs worth documenting
One clue rarely tells the whole story. The pattern, location and freshness of evidence help determine whether activity is current and where it is centred.
Sudden appearance of many metallic flies
Adults gathering at windows
Maggots migrating across floors or dropping from ceiling openings
Unexplained odour from a wall, attic or ceiling void
Activity near waste rooms or meat-handling areas
WHY IT MATTERS
Health, property and operational concerns
- Potential mechanical transfer of bacteria from waste or carrion
- Strong customer and occupant complaints
- Hidden animal carcasses and associated odour
- Secondary pest activity attracted to remains
LOOK-ALIKES
Common identification mistakes
Cluster fly
Cluster flies are dull, slow and associated with overwintering rather than carrion.
Flesh fly
Flesh flies are usually grey with dark striping and a checker-like abdomen rather than metallic.
INSPECTION
How we narrow down the source
A useful pest inspection connects the insect or rodent to harbourage, entry, food, moisture and building conditions.
01
Count whether emergence is sudden and concentrated or just occasional entry
02
Check attics, fireplaces, chimneys and wall void access where safe
03
Inspect waste and recycling for meat or animal material
04
Follow odour and fly concentration to narrow the source
05
Consider recent rodent activity because a poisoned or trapped animal may die in an inaccessible void
06
Check exterior around vents and doors for nearby carrion
PREVENTION
Reduce the conditions supporting activity
Keep meat-containing garbage sealed and serviced frequently
Exclude rodents and birds from structural voids
Maintain screens and door controls
Remove animal carcasses promptly when accessible and safe
Clean waste rooms and compactors
Correct sources before relying on adult fly treatment
PROFESSIONAL CONTROL
What a thorough service plan should address
Product use is only one part of structural pest management. Identification, placement, sanitation, exclusion and follow-up determine whether the result lasts.
01
Identify the fly family first because metallic blow flies point to a very different source than fruit or drain flies.
02
Use the timing and distribution of adults to narrow likely breeding sites.
03
Coordinate carcass removal when accessible; if inaccessible, explain that emergence may continue until development is complete.
04
Use sanitation and exclusion to prevent repeat sources.
05
Apply fly-control products only when they add value after the source investigation.
FAQ
Detailed questions property owners ask
Why did dozens of green flies suddenly appear in one room?
A synchronized emergence often means larvae developed on a dead animal or other concentrated organic source hidden nearby.
Do blow flies mean the house is dirty?
Not necessarily. A single dead mouse, bird or other animal in a wall or attic can produce a sudden population even in a clean building.
Will the flies stop if the carcass cannot be reached?
Eventually, once the available material and developing stages are exhausted. Adult removal and odour management may be needed in the meantime.
Can blow flies spread bacteria?
Because they visit waste, excrement and carrion, they can potentially transfer microorganisms mechanically.
Are maggots on the floor always directly below the source?
No. Mature larvae can crawl away from the feeding site before pupating, so the source may be in an adjacent wall or ceiling void.
What is the best first step?
Confirm the fly type, then search for the breeding source. Killing adults without investigating the source misses the most useful clue the insects are giving you.
REFERENCE SOURCES
Where this information comes from
These pages are written by Emerald Pest Control from authoritative pest, public-health and extension references. They are not copied from competitor websites.
LOCAL PEST HELP
Need help with blow & bottle flies?
Send us a photo or request an inspection. We can confirm the pest, identify the conditions supporting activity and explain the appropriate next step for your property.