Flies in the fall and winter inside

What is with these flies that are lumbering around the office or house during the fall and winter months? Most likely they are cluster flies. These flies overwinter in the nooks and crannies of the walls of an office building or house and become a nuisance during a warm day or throughout certain times of the colder months. The best and most time consuming and expensive way to eliminate them is to build them out. Caulk and seal ever hole that can be found. This becomes a problems when you have a multi story office complex or a suite of offices with open ceiling space above the drop ceilings. Power spraying during certain times of the year outside will help knock the numbers down...on the inside you can use traps and there is a product called the cluster buster that is a window sill trap that uses a powder to act as quick sand and trap the fly. Using a vacuum with a hose attachment will suck them down. The fact is...you can try your best to knock the numbers down...but there may always be that one fly who you will be swatting at every once in a while.