The occasional dusty-looking fly will emerge during the winter, to buzz around groggily, bumping into things. Sleepy flies become more numerous as spring approaches, when they all do their fumbling best to find their way back outdoors and breed up the next generation. Cluster flies are perhaps the least dangerous of the many small creatures that like to share our winter house warmth. What inhabitant of an old frame farm house hasn't stepped or sat on a wasp or hornet . . . Some people are allergic to the chemicals in ladybird beetle juice, and can develop rashes and other symptoms from ladybugs wintering in the walls.
Cluster flies are nothing but a nuisance.
The best remedy is to seal the outside of the home and keep the buzzing pests from getting in in the first place. Not a whole lot but wholesale extermination can be done once cluster flies have joined you for the winter. Any nuisance bug or cluster of bugs gets sucked up and tossed out with the house dust, spilled coffee grounds, dog hair and cobwebs. We discovered that wasps are not asphyxiated by the dust the way flies are and can find their way out. Fresh herbs are best when you have them, but most effective in the long run are plants that retain their aroma when dried.