CENTRAL FLORIDA CRITTER OF THE DAY: Saltmarsh Caterpillar (Estigmene acrea)
In my yard, usually feed on Dogfennel or Elderberry but they can be a pest of some crops and some trees.
You can find them walking through the grass or even along the driveway as this one was. They move very quickly (see video at: http://www.youtube.com/watch?feature=player_embedded&v=BQsGLZNHj84)
If disturbed, they roll up into a ball.
This caterpillar serves as a host: parasitized by tachinid flies
This photo is from a few years back.