HEALTH experts from Kirklees Council have traced the source of a plague of flies in Kirkheaton.
It is believed the flies are coming from a Kirkheaton poultry business, but environmental officers would not confirm the identity.
Fed-up residents were complaining that flies had been filling their homes, schools and businesses for several days.
One woman claimed to have swatted 100 of the creatures in her home in one day.
Experts said the pest was an ordinary house fly, but it was unusual to see so many in December.
Officers from the council's Pollution and Noise Control and Pest Control Sections have met the business owners and are carrying out insecticide treatments today and tomorrow.
Extra non-chemical fly control measures, including electric insect killers, have been put in place.
A council spokes-woman said: "Pest Control officers are now assessing changes which need to be made to minimise the possibility of the fly problem re-occurring and will take action to ensure that these are carried out."
She advised householders in Kirkheaton to keep their doors and windows closed until the problem was over.
She said: "The flies cannot breed inside houses and if they do gain access, they can be easily dealt with by using a fly spray."