I just moved to Lisbon, Portugal recently and pretty soon after we moved into our new apartment (around April), we noticed that the same swarm of flies hung out on the street below every day, getting worse as the weather got warmer.
Every time we open the windows in our apartment one story up, about 20 flies fly in over the course of the day and fly over two spots, one in the sitting room and one in the bedroom. They fly lazily in circles in two groups and never go anywhere else in the apartment, nowhere near bins or the kitchen.
They’re much smaller than blue bottles and larger than fruit flies, they disappear in the evening so I can’t see where they land to take a photo.
If it’s any help, there has been a building site across the road, they flew around under the scaffolding in a huge group and when the scaffolding was taken down they moved closer to our building. There is a restaurant underneath us but there aren lots of restaurants on the street that don’t have a constant swarm of flies!
Any help would be much appreciated to stop them getting in or into on what they are