Black Pepper Black Specks In Bed Sheets. Black pepper mite is a term used for a bird mite. Sound like what you are finding is flea dirt (droppings) you could take some of the black stuff and put it on a wet (white) paper towel if it turns red (dried blood) it is most definately flea dirt.
Three signs that fleas could be lurking in your bed (with pictures): These are called black pepper mites and they are a modern day plague. Young bed bugs have to molt five times before they reach maturity.