The problem has become so bad residents of one Bristol suburb are threatening to withhold their council tax unless action is taken.
The issue is centred in Avonmouth but has reached Shirehampton, Lawrence Weston and Hallen, miserable residents say.
Suffering locals say the flies swarm all over them when they try to relax and are forced to change sticky fly traps every few minutes.
Flies have been a problem in the area in summer before and many blame various nearby waste treatment facilities.
Resident Kerri Reed said: “Living with flies is beyond a joke now.
“There are hundreds in the home no matter what you do. I can’t believe we have to live like this, it’s totally unacceptable.
“Last year the council said there wasn’t a problem, well course there isn’t, because they aren’t living like it.
“Avonmouth is my home and has been for the past 46 years. Never ever have I seen anything like this.”
An unusually warm snap in February brought the flies out earlier this year, but it has generally been a summer phenomenon.
Residents claimed at least one train full of waste trundles through Avonmouth every night bringing more rubbish and more flies.
Liesl Oliver said is impossible to live a normal life in Avonmouth and Shirehampton.
She said: “Basically we can not live a normal day-to-day life with these flies.
“You try and cook? They are there. Try and relax on an evening, they are landing on you constantly. Try and sleep? They are there.
“If I’m not working, my days off are cleaning, bleaching everything, don’t know why I do this though because you could have the cleanest of houses and you’re still affected by them.
“They make you feel dirty.”
Heather Tanton Duncan was one of many residents to say that mealtimes were virtually impossible.
She said: “It’s horrendous.
“As residents we cannot have our doors or windows open for fear of being invaded by the flies. Mealtimes are worse, trying to cook and serve food.
“I have to keep the windows and doors shut in the warm weather to stop them coming in.
“I have to hang that ghastly fly paper in my house and it’s an unbearable living situation.”
Complaints have been sent to Bristol City Council with investigators now looking at the possible source.
Council officer Dylan Davies said: “We are aware of a number of complaints of flies and have been investigating potential sources and monitoring fly numbers year on year across the city.
“There is unlikely to be one particular source but these will include a combination of domestic and commercial waste and facilities where these are processed together with the natural habitat and the flies’ ability to reproduce quickly in favourable conditions such as during warm and wet conditions.
“We have worked with Bristol Waste to consider domestic bins and continue to work with the Environment Agency to investigate and inspect waste facilities in the area to ensure that fly populations are suitably controlled.”
Mr Davies urged people to send in close-up pictures of flies so they could be identified and traced.
“We continue to be vigilant in relation to any potential contributory source and it is helpful if residents provide information so that specific concerns can be investigated further where appropriate,” he said.
“It is useful if the particular fly causing issues are identified as certain fly types are associated with particular sources, so this aids investigation.”