Black Spots on the Walls After Spraying for Bed Bugs | Hunker
Bed bugs suck the blood of warm-blooded animals during the night. After they have a nocturnal blood meal, they digest the substance and eliminate it. The bug's defecation can leave behind small black, red or brown spots on walls, along baseboards, mattresses or other home surfaces. A large infestation of the pests can leave behind considerable staining.