Start by keeping food waste contained. Tie garbage bags securely and wrap especially attractive waste such as meat and fish scraps before putting them in the bin. During very hot weather, some households freeze particularly smelly scraps until collection day. Most importantly, keep the lid properly closed so adult flies have less opportunity to reach the contents.

Moisture also contributes to the problem. Avoid pouring liquids into the trash, and consider placing absorbent newspaper or cardboard at the bottom where appropriate. After collection, remove any remaining food residue, wash the container with detergent and water, and allow it to dry thoroughly before adding another bag. Keeping an outdoor bin in a shaded location can also reduce excessive heating.

If maggots have already appeared, remove the garbage first. The bin can then be thoroughly cleaned with hot, soapy water, paying attention to corners, the lid, and areas where residue collects. Follow the cleaning-product directions and never mix household cleaners such as bleach with ammonia or acids.

The simplest prevention strategy is therefore surprisingly ordinary: remove food regularly, contain it securely, keep the lid closed, and clean spills quickly. Flies need access to suitable material to lay their eggs. Make that material difficult to reach, and you’re far less likely to open the lid on a summer morning and discover an unwanted colony waiting inside.