[uujudy]

Ants, gophers OR Gopher Tortoises.
When we went horseback riding in the Ocala National Forest we saw many of those mounds. Our guide said they were Gopher Tortoise mounds, where the tortoises go to lay eggs, sleep at night or play poker. She cautioned us to keep the horses from stepping on the mounds so we wouldn't squash the tortoises. The mounds are connected by tunnels, and the tortoises are considered to be a 'keystone species' because so many other critters depend on their tunnels. If you see the mounds in a line (like a connect-the-dots picture), odds are they're tortoise mounds. http://en.wikipedia.org/wiki/Gopherus_polyphemus
(I'm just guessing, but would that be where 'turtle mound' comes from?)