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.
We would recommend our Overwintering Kit for Stink Bugs, Lady Bugs, Boxelder Bugs. The Overwintering Kit contains a combination of professional products to protect your home from a variety of insects including stink bugs (including the brown marmorated stink bug), kudzu bugs, lady bugs (Asian beetles), box elder bugs, pill bugs and more. The Overwintering Kit includes two insecticides and a dust applicator to keep stink bugs and other overwintering pests at bay. Bifen IT is a water based insecticide concentrate that offers a long-term residual effect. CimeXa Insecticide Dust contains amorphous silica gel, which acts as a desiccant when insects crawl across it. Dust is extremely stable, but it is only for use in voids and areas where it will not be easily disturbed or picked up by people or pets. This kit includes 1 x 4 oz bottle of Bifen IT Insecticide, 1 x 4 oz. bottle of Cimexa Dust, and a hand duster for easy application.
We have a great Overwintering Kit to help control Asian lady beetles, stink bugs, and other overwintering pests. This kit includes a residual spray called Bifen IT, plus CimeXa Insecticide Dust and an applicator. You will need a hand pump or backpack sprayer to apply the Bifen IT. We have more tips in our Asian Lady Beetles Treatment Guide here.
Our Overwintering Kit for Stink Bugs, Lady Bugs, Boxelder Bugs contains a combination of products that are great to treat for those overwintering pests, like boxelder bugs.
We would recommend using our Overwintering Kit for Stink Bugs, Lady Bugs, Boxelder Bugs. The kit contains a combination of professional stink bug control products to protect your home from a variety of insects including stink bugs (including the brown marmorated stink bug), kudzu bugs, ladybugs (Asian beetles), box elder bugs, pill bugs and more. This kit includes two insecticides and a dust applicator to keep stink bugs and other overwintering pests at bay. Bifen IT is a water-based insecticide concentrate that offers a long-term residual effect of 90 days indoors and 30 days outdoors. CimeXa Insecticide Dust contains amorphous silica gel, which acts as a desiccant when insects crawl across it. Dust is extremely stable, but it is only for use in voids and areas where it will not be easily disturbed or picked up by people or pets.
For stink bug and lady bug control, we recommend our Overwintering Kit for Stink Bugs, Lady Bugs, Boxelder Bugs.