The blue bottle fly is a large, metallic blue blowfly found across much of the world. Officially named Calliphora vomitoria, it belongs to the blowfly family and is roughly twice the size of a common housefly, measuring 10 to 14 mm long. If you’ve spotted a loud, buzzing fly with a shiny blue body indoors or hovering around garbage, this is almost certainly what you’re looking at.
How to Identify a Blue Bottle Fly
The most striking feature is the bright metallic blue abdomen, often with faint black markings. The head and thorax (the midsection behind the head) are dull gray, and the body and legs are covered in black bristly hairs. The eyes are red, the wings are transparent, and the antennae are short and black.
The easiest way to confirm you’re looking at a blue bottle fly rather than a closely related species is to check for orange “cheeks.” These are tufts of orange hair just below the eyes, sometimes described as giving the fly an orange-bearded appearance. A near-identical relative, Calliphora vicina, lacks these orange hairs and has a yellowish base at the wing instead of the dark base seen on the blue bottle fly.
Blue Bottle Flies vs. Green Bottle Flies
Both blue and green bottle flies are blowflies with metallic coloring, and they’re roughly the same size. The difference is straightforward: blue bottle flies have a vivid blue abdomen, while green bottle flies (Lucilia sericata) are metallic green, though they can sometimes appear blue-green. Green bottle flies are especially common around pet feces outdoors, while blue bottle flies are more strongly drawn to animal carcasses and rotting meat. If you’re seeing metallic flies clustered around a dead animal or hovering near a trash can with meat scraps, blue bottle flies are the more likely culprit.
What Attracts Them
Blue bottle flies are drawn to the smell of decomposition. They lay their eggs on dead animals, rotting food, exposed garbage, and sewage or compost piles. Female flies can detect decaying organic matter from a surprising distance, and they zero in on it quickly to deposit eggs. Common outdoor attractants include roadkill, dead birds or rodents near a home, uncovered trash cans, and compost bins with meat or dairy waste.
Indoors, the most common trigger for a sudden cluster of blue bottle flies is a dead animal you can’t see. A mouse or bird that died inside a wall, crawl space, attic, or beneath a major appliance will attract egg-laying females, and within days you can have dozens of flies emerging inside the house. If you’re seeing many blue bottle flies indoors with no obvious food source, a hidden carcass is the explanation worth investigating first.
Life Cycle and Reproduction
Blue bottle flies develop through four stages: egg, larva (maggot), pupa, and adult. Females lay eggs directly on decaying organic material, and the eggs hatch quickly, often within a day in warm conditions. The larvae feed on the surrounding decomposing tissue, growing through three stages before crawling away from the food source to pupate in soil or a dry, sheltered spot. After pupation, adult flies emerge ready to mate and restart the cycle.
Temperature has a major influence on how fast this process plays out. In warm weather, the entire cycle from egg to adult can complete in as little as two to three weeks. Cooler temperatures slow development significantly. This is why blue bottle fly problems tend to spike in spring and summer, and why a dead animal in a heated wall void can produce flies even in winter.
Health Risks
Blue bottle flies aren’t just a nuisance. Because they feed on decaying animals, feces, and garbage before landing on your food or kitchen surfaces, they can carry a range of harmful bacteria. Blowflies as a group are associated with the transmission of Salmonella, E. coli, Campylobacter, and even anthrax spores in agricultural settings. They pick up pathogens on their body hairs and feet and deposit them wherever they land next.
In rare cases, blowflies can also cause myiasis, a condition where larvae develop inside living tissue. This happens when eggs are laid on an open wound or broken skin, and the hatching larvae feed on the surrounding tissue, causing damage and secondary infections. Myiasis from blue bottle flies is uncommon in humans and far more of a concern in livestock, but it’s another reason to keep wounds covered and manage fly populations around the home.
How to Get Rid of Them
The single most important step is finding and removing the breeding source. Killing adult flies will reduce what you see in the short term, but new flies will keep emerging until the material they’re breeding in is gone. If blue bottle flies are appearing indoors, check for dead rodents or birds in walls, crawl spaces, attics, basements, under cabinets, and behind large appliances like refrigerators or washing machines. Outdoors, look for animal carcasses near the foundation, and inspect garbage cans and compost piles.
Once you’ve removed the source, a few practical measures will clear out remaining flies and prevent new ones from returning:
- Screening and sealing: Make sure all windows and doors have tight-fitting screens without tears. Seal gaps around door frames, vents, and utility openings.
- Sticky traps: Fly glue traps hung in garages, basements, or near windows where flies congregate will catch adults passively without chemicals.
- Sanitation: Keep garbage cans and dumpsters tightly lidded and clean them regularly. Don’t leave pet food, meat scraps, or compost with animal products exposed.
- Moisture control: Reducing excess moisture around the home, especially near drains and compost areas, makes the environment less hospitable for egg-laying.
- Contact sprays: Pyrethrin-based aerosol sprays provide a quick knockdown of adult flies in enclosed spaces. These kill on contact but don’t offer lasting protection.
- Residual treatments: For persistent problems, applying a residual insecticide around entry points and fly resting areas once a month can reduce the number of flies making it inside.
Chemical control alone rarely solves a blue bottle fly problem. If flies keep appearing after you’ve sprayed, the breeding source is still present somewhere. In homes with recurring infestations and no visible cause, it’s worth having a pest professional inspect for rodent activity in walls or attic spaces, since a rodent problem and a blue bottle fly problem often go hand in hand.