Dan from Marinette writes
It sounds like you may be dealing with cluster flies. This is a common over-wintering pest that will gather on the warm, sunny sides of structures to look for places to hide for the winter. We have an Overwintering Pest Kit that includes a liquid spray (Bifen IT) and an insecticide dust (Cimexa) for a 2-part barrier treatment against these pests.
Answer last updated on: 10/17/2017
