It can be difficult to detect bed bugs as they hide in crevices and cracks, and are extremely small in size. However, you can detect the evidence of bed bugs on your mattress and bedding. Live bed bugs have a habit of leaving a cluster of black or dark brown spots of dried excrement on the surfaces that are infested with the bed bugs. These bugs also exude a musty and subtle odor. You can easily find the bed bugs on non-infested dwellings.