Hummingbird and Butterfly Gardening: Red Admiral Nettle Butterfly ?, 1 by Sami

Sami wrote:
I think this is a Red Admiral Nettle Butterfly. We were sitting out on the deck and noticed a couple butterflies and bees swarming a place on the Red Southern Oak Tree in the back yard, They all seem to want to be in the same spot. So at a closer inspection we noticed that there was a small hole in the tree. The butterflies and bees and some ants were eating from this spot and fighting each other to get to what ever was there. Can someone explan this to us and verify that this is truly a Red admiral Nettle butterfly. This has been going on for a couple of days now. In the spot it seems to be red inside the hole that all so desperately want to stay.
Here is a picture of the butterfly

Sami