I the white coloured bug that I can think of that is detrimental are mealy bugs. Maybe to a image search and see if they look like what you have? I hope you don't have them because they seem impossible to get rid of permanentely.
....not all bugs are harmful, so don't panic too much. Centipedes only eat other bugs, and millipedes only potentially will eat roots but I think they prefer decaying mix. I really doubt a small millipede will eat roots (maybe just a root hair on a paph), maybe those huge ones found in the tropics