The bigger the black hole, the slower it evaporates. By the time you get up into planetary sizes they basically don't change mass on the time scale of stars. (From this wonderful calculator [0], a black hole with a mass of 6.0x10^24 kg - about that of the earth - would have a lifetime of ~5.75x10^50 years)

So if there's a 1-20 Earth-mass black hole out there, it hasn't evaporated from anything appreciably larger to get to that point.

0: http://xaonon.dyndns.org/hawking/