Dio,
Do these little critters display a rather amazing jumping ability? If so,
it sounds like they're probably springtails - very primitive insects, and
perfectly harmless. If you look at one with a good magnifying glass (if
you can catch one) you should see a "tail" folded up under the rear portion
of the body. This structure is used for the jumping movements.
Good luck,
Liane Cochran-Stafira