Yikes!! I believe this is a Banded Argiope,
Argiope trifasciata. I thought of holding my index finger near it to indicate the size of the monster, but I was a little afraid of being taken hostage. You can learn more about this spider and others
here. (Burning Silo is a terrific blog -- be sure to look around while you're there.)
Public Service Announcement: while I was warily photographing the giant mutant spider, I met a woman looking for her lost dog. Here are a couple of photos. If you see Bess, please leave a comment here and I'll get in touch with her owner.
Finally, please note that there will be no outing this week at the Beechwood Site, but we'll be back at it next week.