Trichonephila clavipes (formerly known as Nephila clavipes) is an orb-weaving spider species which inhabits forests and wooded areas ranging from the southern US to Argentina.
They are not known to be aggressive towards humans, only biting out of self-defense if touched, and their relatively harmless venom has a low toxicity.
Trichonephila clavipes females are some of the largest non-tarantula spiders in North America, ranging from 24-40 mm in length when fully developed.
Males are much smaller (6-8 mm).
This spider is relatively easy to recognize. 
They have a silvery white cephalothorax (head and neck area) and a longer orange-brown abdomen with two rows of small white-yellow spots. 
Their legs consist of dark yellow and brown banding, and the first, second, and fourth leg pairs also contain black brush-like tufts of hair near the joints.

Shark Valley, Everglades National Park, Florida, USA, 23 November 2012