Flies are among the most widespread insects worldwide. Several hundred species are known in Central Europe alone – from the well-known housefly (Musca domestica) to smaller fruit flies (Drosophilidae). In the wild, they take on important ecological tasks, such as decomposing organic material or acting as pollinators. But as soon as they enter houses and apartments, the question arises: How relevant are flies indoors from a biological, hygienic and health perspective – and at what point does their presence become problematic?
Between ecosystem and living space
In the natural environment, flies make a crucial contribution to biological balance. They decompose organic material, serve as food for birds or amphibians and take part in certain pollination processes. However, these functions no longer apply as soon as the animals are indoors.
There they encounter an environment in which their biological tasks appear alienated: garbage residues, traces of food, plants or warm layers of air invite them to reproduce and search for food. Houseflies and blowflies in particular can multiply quickly – and thus develop into a hygiene risk factor.
Even a single specimen lays up to 150 eggs in just a few days. The larvae find optimal conditions in warm kitchens, pantries or on organic waste. Particularly critical: Flies can act as mechanical transmitters of germs – including through contact with contaminated surfaces, feces or waste.
Hygiene problems and potential health risks
Flies have fine adhesive pads on their feet and are therefore able to pick up and pass on microorganisms along their paths. Studies show that typical household flies carry pathogens such as Salmonella, E.coli or Staphylococci can be transported – albeit in a comparatively low concentration. However, there is an increased risk, particularly in kitchens or medically sensitive rooms.
Added to this is the potential exposure to allergens: In some cases, components of fly saliva, feces or dead body parts can trigger allergic reactions. For people with respiratory diseases or weakened immune systems, repeated occurrences of flies can be an additional stress factor.
Protection through structural measures
Patio or balcony doors are a common entry point for flies – especially in the summer months. Open doors with simultaneous incidence of light have a great attraction for the animals. This makes it all the more important to have mechanical protection that prevents insects from entering without blocking the exchange of air.
A proven approach is to install a custom-fit Fly screen on the patio door by Lysel. These solutions can also be retrofitted and reliably keep flies, mosquitoes or other insects away – without the use of chemicals. On flyscreen.org You will also find further information on selecting suitable systems for different installation situations.
Light, smells and temperature – what attracts flies
Flies orient themselves largely through smell and temperature differences. Fermenting fruits, garbage, Leftover food or plants on the windowsill can act as a source of scent. In conjunction with warm room zones and light sources, ideal conditions are created.
A well-known strategy is to avoid light sources near open doors and windows – especially in the evening hours. At the same time, it is advisable to dispose of organic waste promptly, keep kitchen sinks clean and, if necessary, check house plants for mold or damp soil.
Behavior and lifespan
An often underestimated aspect in everyday life: the lifespan of a common housefly is up to 30 days under optimal conditions – during which it can reproduce several times. This means that even a single unnoticed infestation can quickly lead to a small population.
Flies typically prefer to stay in warmer, easily accessible areas. Window sills, fruit bowls or open beverage containers are preferred. Depending on the species, the animals can also be nocturnal – which makes their perception more difficult and combating them even more complicated.
Insect-friendly rooms or sterile zones?
Some voices from environmental and urban ecology advocate that flies and other insects should not be generally excluded from living spaces – but rather tolerated in certain areas. In fact, wild bees, beetles or even butterflies can occasionally be observed in homes without causing a hygiene problem.
When it comes to flies, however, there is a lot to be said for a controlling attitude: their behavior, their reproduction speed and their proximity to potential sources of germs make them rather unwanted guests. While a one-off housefly doesn’t cause much damage, a regular occurrence can become a problem.
The aim should therefore not be to completely isolate oneself from nature, but rather to achieve a functional balance between air circulation, incidence of light and insect protection. Mechanical barriers such as fly screens from Lysel, a brand that is best known for its high quality standards, fulfill this purpose unobtrusively and effectively – also in the sense of sustainable, chemical-free indoor management.
Conclusion: tolerance with limits
Flies are part of a functioning ecosystem – but indoors, their biological functions intersect with hygiene challenges. Although they are not classic disease vectors, their potential to spread germs and expose them to irritants makes them a risk that should not be underestimated.
Long-term protection through mechanical solutions is particularly worthwhile when doors or windows are open. Weatherproof fly screens from Lysel help maintain the balance between humans and insects – by reducing unwanted encounters in the living space without essentially shutting out nature.
01/06/2026