The infestation of insects in the Pengam Green and Tremorfa areas has left some residents fearful of opening their windows during the summer.
Others posted photographs of large numbers of flies caught in fly traps at their homes and described the problem as “horrendous”.
“Have had to put up with this the last two years!”, wrote one Twitter user. “It has caused me severe stress. Unable to open windows! They even get in when windows are closed.
“Had three days off work sick last week with sickness. Fighting flies off food when you’re cooking. Landing on your food when eating!”
Another added: “Absolutely horrendous around here... the flies landing on my baby while he slept yesterday, it’s too hot to keep everything closed.”
On Thursday , Huw Thomas, the leader of Cardiff Council, announced the source of the infestation had been traced to food left in steel tins awaiting processing at the nearby Celsa steel works.
Thanks for the info, these were up less than a week 🤢 pic.twitter.com/HAaCl1SBYP— Danielle Hill (@danmariehill)July 18, 2019
Glad you found the source. Last year I thought it was the heat. We got fly traps. And this was after an afternoon. It was crazy. pic.twitter.com/m91eppgDGR— Studio T (@StudioT_UK)July 19, 2019
He said the company would avoid bringing food-contaminated steel to the site in future.
Natural Resources Wales, a Welsh government body, is also writing to explain the issue to affected residents and offer pest control materials.
Dr Gareth Richards, industry and waste regulation specialist from Natural Resources Wales, said: “We regulate businesses to make sure they operate without harming people and the environment.
“We’ve worked with Cardiff council to trace the source of the fly problem in the Tremorfa area of Cardiff to the nearby Celsa steelworks, which we regulate.
“The issue is related to scrap tins stored on site with residual food contamination.
“Celsa is implementing a number of measures to reduce and ultimately avoid the impact this issue is having on the local community.”