Herpetogramma sp..
Size: approx. 20 mm. Photo: 08/07/14, 10 pm.

Herpetogramma has 10 species in North America. The caterpillars are often called webworms or sod webworms. Most species feed on grasses and some on ferns. This specimen is perhaps H. phaeopteralis (tropical sod webworm) which is a destructive pest of warm season turfgrasses in the southeastern US (see second link). 
bug guide (this photo):