These little magical nymph creatures dwell in the ground and plants, hiding away until they're ready to jump out and surprise whoever or whatever may be standing nearby.
They are crafty creatures, often using tricks to get their way or serve whatever purpose they may be seeking, and are known to vanish in anger at the slightest inclination.

Dryad Sprites specifically seem to like hiding in crops and other harvestable plants and jumping out at unsuspecting farmers, ready to play a game.
Use the correct type of hoe on them based on the signal they give, and they might reward you.