Cluster flies are just slightly larger than the average housefly. They are also considerably less dangerous, as they do not lay their eggs in human food, but rather in worms. The problem with cluster flies occurs in colder climates, when they seek shelter in people's homes where it is warmer. They tend to travel in packs of hundreds, or even thousands, which can cause problems for homeowners. It is fairly easy to remove cluster flies from a home. It must be done quickly, though, because once the flies are disturbed, they will swarm and move on to another part of the house.
Find out where the cluster flies are hiding. These flies enter a home because they are looking for a place to hibernate, so finding them may not be as easy as you think. Spotting one group of cluster flies may not solve much if there are others in various areas of your home. Do a quick sweep of attics, basements, closets and unused areas of your home, as cluster flies are attracted to these places.
Take a can of insect repellent and quickly spray the infected areas. You need to be quick, because chances are there will be many flies to get rid of, all of which are easy to provoke. Luckily, the insect repellent will work almost immediately.
Use a vacuum to get rid of the remaining flies in the area you sprayed with insecticide. Use the vacuum to suck up remaining flies, both dead and alive. Be quick, though, because you don't want them to move to a different part of the house.
Spend some time sealing off any small gaps in the sections of your home that were infested. This will help prevent future swarms of cluster flies from entering your home.