Scholars generally treat flies and mosquitoes as potential carriers of ritual impurity — if they contact wet najāsa and then touch your food, the food may be considered impure and should be cleansed.
 
                    If a fly or mosquito lands on something that is clean, it renders that object impure. The reasoning is that flies live in unclean places — sewers, carcasses and rubbish — and their bodies are laden with microbes and contamination.
If a fly or similar insect sits on a wet impure substance and then on a clean object, the clean object is not automatically impure — because the insect’s feet may not necessarily pick up moisture. However, if it is known that the impurity was carried and transferred, the object becomes impure.
When a fly lands on a clean item such as food or dishes, it can transfer microbes and impurities from those filthy places to the surface.
Therefore, if a fly sat on impure matter (for example animal excrement or urine) and then on your food, that food becomes impure and should be washed to become ritually clean.

Below is a converted, clear table of the prevention tips the article lists.
| Preventive measure | Short explanation | 
|---|---|
| Keep the home clean | Flies seek food and moist places to breed; remove garbage and food waste to avoid attracting them. | 
| Use screens and nets | Window screens and mosquito nets block flies from entering living spaces. | 
| Store food in closed containers | Keep food sealed so flies cannot land on or enter it. | 
| Eliminate flies if necessary | Use insect sprays, fly traps or electric fly killers as last-resort measures. | 
| Consult religious authorities | For detailed rulings on najāsa and purification, always ask qualified jurists or local scholars. | 
| Tip | Short explanation | 
|---|---|
| Wash food if a fly has sat on it after contacting najāsa | If it’s known the fly contacted impure matter and then the food, wash the food to remove impurity. | 
| Keep food covered and sealed | Prevent flies from landing on exposed food by using lids and containers. | 
| Install screens and nets | Prevent insects from entering living spaces where food is prepared or eaten. | 
| Maintain household cleanliness | Remove waste and standing moisture to reduce fly attraction and breeding. | 
| Consult a qualified authority for rulings | For specific questions about ritual purity and fiqh, ask recognized religious scholars. | 
 
                                                        