Flies: Houseflies and Bluebottles

Houseflies and bluebottles are among the most common flying pests found in UK homes during warmer months. While both belong to the same broad family of insects, they have different habits and breeding preferences. Understanding these differences can help you work out where an infestation is coming from and how best to deal with it.

Telling them apart

Houseflies are grey with four dark stripes running along their thorax. They measure around 6 to 7mm in length and have large reddish compound eyes.

Bluebottles are slightly larger, typically 10 to 14mm, and have a distinctive metallic blue or blue-green sheen across their body. This colouring makes them easy to spot, even at a glance.

The larvae of both species look similar: pale, legless maggots that taper towards the head. Bluebottle maggots are often larger when fully grown, though telling them apart by size alone can be tricky. In practice, the location and food source usually give a better indication of which species you are dealing with, though this is not always straightforward without closer inspection.

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Breeding habits and lifecycle

Houseflies breed in moist, decaying organic matter. Common breeding sites include household waste bins, compost heaps, animal manure and rotting vegetation. A female housefly can lay several hundred eggs over her lifetime, depositing them in batches on suitable material.

Bluebottles strongly prefer dead animals, raw meat and fish for egg laying, though they will sometimes use other decaying organic matter when these are unavailable. This preference for carrion is why bluebottles are sometimes called blowflies. If you notice bluebottle maggots indoors, it often indicates a dead animal somewhere nearby, perhaps a mouse or bird in a wall cavity, loft or chimney.

Both species develop quickly in warm conditions. The full lifecycle from egg to larva to pupa to adult can take less than two weeks when temperatures are high. This rapid reproduction explains why small problems can become larger infestations in a short time if the breeding source is not removed.

Adult houseflies are capable fliers and can cover considerable distances, though most remain within a mile or so of their breeding site under normal circumstances. This means flies entering your home may not necessarily be breeding on your property. However, if you are seeing large numbers regularly, a local source is more likely.

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Why they matter

Both houseflies and bluebottles can carry bacteria and other pathogens on their bodies and legs, transferring them to food and surfaces as they land. Houseflies in particular move frequently between waste material and food preparation areas, which creates a risk of contamination.

Bluebottles are often associated with hygiene concerns in food premises. Environmental health officers may investigate if bluebottle activity suggests problems with waste storage or the presence of decomposing material.

Both species also play ecological roles as decomposers and as food for other animals. However, inside homes and food businesses, these benefits do not outweigh the hygiene risks they pose.

For most households, occasional flies are not a health emergency. But persistent or heavy infestations should be addressed, both for comfort and hygiene reasons.

Practical steps for control

Reducing fly problems starts with removing or managing breeding sites. For houseflies, this means keeping bins clean and tightly closed, disposing of food waste promptly and managing compost heaps so they do not become too wet or exposed. Cleaning up after pets quickly also helps.

Habitat modification around your property makes a difference too. Keep gardens tidy, clear fallen fruit from beneath trees, and store rubbish bins away from doors and windows where possible. These measures reduce the attraction for flies in the first place.

For bluebottles, the priority is finding and removing the source. If you are seeing large numbers indoors, check lofts, wall cavities, chimneys and under floorboards for dead animals. A persistent smell may point you towards the location.

Physical barriers can help keep flies out. Fit fly screens to windows and doors if you tend to leave them open in summer. Keep food covered, clean up spills quickly and do not leave pet food sitting out for long periods.

Sticky fly papers and UV light traps can reduce adult fly numbers indoors. These are available from most hardware shops and supermarkets. Electronic fly killers are particularly common in commercial kitchens and food preparation areas, where they provide continuous control. Insecticidal sprays labelled for flying insects may provide short term relief but will not solve the problem if the breeding source remains.

If you are dealing with a persistent infestation that you cannot trace or control yourself, consider contacting a professional pest controller. The British Pest Control Association maintains a directory of qualified technicians. Many local councils also offer pest control services, though charges and availability vary, so check with your local authority for details.

For businesses, particularly those handling food, fly control is a legal requirement under food hygiene regulations. Guidance on compliance is available from the Food Standards Agency and your local environmental health department.

The Next Step

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