Why do I have flies in my house during winter?

I have been inundated with calls over the last few weeks for flies in homes and businesses. Most of the calls are from people worried that the flies are caused by a dead rodent trapped somewhere in the property.  To the untrained eye cluster flies look very similar to what you would expect to see if a rodent was rotting away somewhere, however this is not the case.

Cluster flies are an outdoor insect that is seeking shelter from the approaching winter weather, they are often found around window frames and in loft spaces where they "cluster" together over the winter period . Treating them is relatively simple, however until there has been a hard frost, more flies will keep finding their way in. I usually recommend waiting until after the first hard frost of the year prior to treating them. After this time all the flies that have not found shelter should succumb to the elements.