This is a Gasteracantha cancriformis. It has many different common names, including star spider, spiny orbweaver spider, crab-like orbweaver spider, jewel spider, spiny-bellied orbweaver and jewel box spider, and it is found throughout the tropics.
Image source: http://www.flickr.com/photos/diazseptsix/5940340318/
Gasteracantha cancriformis In Louisiana & Mississippi
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