You can detect bedbugs bug looking for black tracks on your bedding and mattress (look at the top of the mattress in the picture below). These tracks are actually fecal stains that bedbugs leave when they move. Because bedbugs feed on human blood, their feces is pretty much nothing more than dried blood.
Sometimes while a bedbug is feeding you will move or turn over. If the feeding bedbug is crushed when you move, it will leave small blood stains on whatever they are squished against. Obviously, bedbug fecal stains and blood stains show up best on lighter colored bedding.
You also may have bed bugs if you start showing bed bug bite symptoms.
Bedbugs tend to come out later at night as they feed closer to dawn. So if you find yourself awake late at night or early in the morning, you might be able to more easily find a bedbug.
Make sure you have a flashlight. Gently check the sheets while you are still in bed. Then carefully pull back the bedding and mattress cover near the head of the bed and use the flashlight to check the seams and piping of the mattress.
If you get up and move around, it might alert bedbugs that something is up and give them time to scurry away into their hiding places. If you’re having trouble seeing an actual bedbug, read How to Trap Bed Bugs.
Chances are you won’t see bedbugs during the day unless you have a very bad infestation. Bedbugs do move around during the day but are known to more around more at night. Between that and their tiny size, it could take some luck to see them out during the day.