It’s a girl crab (spider)!
University of Florida’s Featured Creatures describes the spineybacker orbweaver (Gasteracantha cancriformis) as “one of the most colorful spiders in Florida” and as “one of the most conspicuous.” The information in this post comes from that source.
This spider usually is found in mixed woodlands (as at the Oslo Riverfront Conservation Area) or citrus groves. The photo above was taken in our front yard, and the web was connected to wild coffee (Psychtoria nervosa) and silver-blue saw palmetto (Serenoa repens).
Female spineybacker orbweavers can be up to 1/2″ wide and 1/3″ tall. The top of the abdomen (dorsum) is white with black spots with 6 red pointed abdominal projections called spines.
Males are smaller and have a gray dorsum marked with black spots. Males lack spines but have 4 -5 small humps on their posterior.
Their webs have tufts of fluff. No one knows for sure quite why.