A plague of flies in Cardiff has been traced to scrap food tins being stored at a steelworks in the city, according to officials.

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!”

In pictures: Thousands of bees swarm Topshop Show all 8 1 /8 In pictures: Thousands of bees swarm Topshop In pictures: Thousands of bees swarm Topshop UK A woman huddles up as she walks past a swarm of about 5,000 honeybees that have been attracted to a discount sign on the window of a shop in central London turning the fashion store display into a carpet of insects In pictures: Thousands of bees swarm Topshop UK Passers by check out a swarm of about 5,000 honeybees In pictures: Thousands of bees swarm Topshop UK It is understood the unusual nesting place was picked by the Queen bee, who landed there first and was quickly followed by her devoted colony In pictures: Thousands of bees swarm Topshop UK The swarm of 5,000-strong honeybees on the window of Topshop in Victoria Street, central London In pictures: Thousands of bees swarm Topshop UK The swarm of 5,000-strong honeybees that were attracted to a discount sign on the window of Topshop in Victoria Street, central London, are put into a box by bee keepers from the John Lewis Partnership and Westminster Cathedral, to be transported across the road to the roof of Westminster Cathedral In pictures: Thousands of bees swarm Topshop UK The swarm of 5,000-strong honeybees that were attracted to a discount sign on the window of Topshop in Victoria Street, central London, are put into a box by bee keepers from the John Lewis Partnership and Westminster Cathedral, to be transported across the road to the roof of Westminster Cathedral In pictures: Thousands of bees swarm Topshop UK The swarm of 5,000-strong honeybees that were attracted to a discount sign on the window of Topshop in Victoria Street, central London, are put into a box by bee keepers from the John Lewis Partnership and Westminster Cathedral, to be transported across the road to the roof of Westminster Cathedral In pictures: Thousands of bees swarm Topshop UK The honeybees are carried in a box by bee keepers from the John Lewis Partnership and Westminster Cathedral

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.

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.