Villages in Russia’s Urals region have been invaded by vast swarms of flies that have sparked health concerns and fears for local harvests.

“You can’t hang out your washing to dry or open your windows, let alone go outside,” a woman in Lazorevy told state television, which aired images of thick clouds of flies crawling and buzzing through the village.

Another local was shown sweeping up piles of dead and dying flies from the floor of his home. “Every day or two there’s enough to fill a bucket, half a bucket,” he said. Residents described scenes as “like something from a horror film”.

“It’s unbearable, the flies are everywhere,” said a woman holding a wailing child in her arms. “I’m afraid for my children. We need to poison the flies constantly [with chemicals], but then we all have to breath that air. It’s frightening.” State TV also said the flies could infect people with diseases.

Reports said the invasion began after a farmer illegally used tonnes of chicken droppings from a local poultry farm as fertiliser, in which flies laid millions of eggs. Some reports said dead chickens and chicken entrails had also been used. Investigators confirmed they had opened a criminal investigation into the unsanctioned use of “environmentally hazardous waste”.

Maxim Maksimov, the head of the poultry farm, admitted supplying chicken droppings to the farm for use as fertiliser, but said it was normal practice. “This is much better than chemicals,” he told the Ura.ru news website. “We were just unlucky with the weather. A wet spring and then a sudden increase in temperatures created favourable conditions for flies to breed.”

He said that he had ordered his workers to cover the farmer’s fields in a bid to prevent flies laying more eggs in the droppings. “If this doesn’t work, we are prepared to use special agrochemicals on the villages.”

The farmer, Andrei Savchenko, denied he was to blame. “Flies have existed for millions of years, and they are everywhere,” he said. “This is just a question of the amount of them. But no one can tell me what the acceptable or cut-off number of flies is.”