SWARMS of flies have been coming in from the cold in Kirkheaton.
Disgusted residents have been reaching for swatters and demanding Kirklees Council find the source of the filthy pests attracted to their warm homes.
Householder Ann Raddings, 43, said schools, shops, pubs, the library and many homes had all been affected.
She killed 50 flies in her bedroom one morning and swatted 100 in her home another day.
"The flies are sporadic. You get a mass one day and nothing the next.
"One day these flies just appeared out of nowhere.
"It has never, ever happened before."
Kirklees Council's pest control staff have been investigating the widespread problem for several days following complaints from residents.
An entomologist identified the pest as an ordinary house fly.
"It is very unusual to have so many in December," said a spokesman from the council's pest control department.
"We are confident that we have now found the source of the flies and we are working with the people concerned to give advice on how to solve the problem."