Question: I have black fleas in my house. I have tried sprays, foggers and everything else. Nothing seems to work. Why is it so hard to kill these fleas?

ANSWER Probably what you have are springtails. This is a good name for them, since they hop by using their tail. They are often found in moist locations outside houses, and sometimes inside (kitchens, bathrooms, ground-level rooms). 

Springtails do not bite people or pets, but they can be a nuisance when they occur in large numbers. These are the same insects that can appear in large numbers in the winter on snow, then they are called snow fleas.

More information on springtails