Thanks. The differences in patterns on the back of the abdomen among the photos of Eris militaris in BugGuide are certainly greater than the minor differences between my photo and the ones in BugGuide. Part of the difficulty with my photo is that the spider is scrunched up in a defensive posture.

Variations within adult males (which is what you have here) are pretty subtle at first, so I wonder if the variation you notice is between
adult males:
and immature or female specimens: ?

If the differences you notice are all with adult males, that's great! Most people aren't that observant. If you stare at them long enough, the variations really do stand out. Unfortunately they aren't worth much due to the nearly identical, similarly variable, and rarely encountered species Eris rufa, which has also been recorded in North Carolina.

E. rufa's habitat appears to be restricted to pine foliage, so if your little guy wasn't found on a pine tree I'd bet money that it's E. militaris, as Lynette suggested.

I found the spider on Gerardia, when I was looking for Buckeye caterpillars. So that makes it clear, it is E. militaris. Thanks for the tip.