Bed bugs are reddish-brown, flat and shaped like an apple seed. Carpet beetles vary in color depending on type (e.g., varied, black, furniture or common carpet beetles). Sometimes they look like a black and yellow ladybug.
Look for the bugs themselves or their bloodstains, especially along the seams of mattresses. Further, look for dark spots of insect waste where bedbugs might crawl into hiding places on furniture
Bed Bug Poo. Unlike blood stains, fecal spotting tends to be black or dark in color. The stains are from partially digesting blood and clustered in groups in areas that bed bugs inhabit. The spots will smear if wiped with a wet rag. Evidence of fecal spotting is usually visible in their typical hideouts, like along mattress seams, box spring edges,
All the fecal traces I saw from bed bugs were one of the two types of spots I've described before: the stains that look like a permanent marker with its cap off bled into the fabric or the little tar-colored dots that look like a very dark black, matte version of candy dots.
Dark spots (about this size: •), which are bed bug excrement and may bleed on the fabric like a marker would. Eggs and eggshells, which are tiny (about 1mm) and pale yellow skins that nymphs shed as they grow larger.
Bed bugs will leave black fecal spots (basically dried, digested blood) around the places they're hiding. They're usually found in close proximity to their food source, i.e., people, Curtis says, which is why they're typically in beds, furniture, and carpeting.