This ant was busy on the blossoms of the swamp milkweed, a native species which is different from the common milkweed, as the swamp milkweed has pink flowers and long narrow leaves.
Butterflies, bees and hummingbirds are not the only creatures going after the flower blossoms for nectar. Other insects are drawn to blossoms, including this ant on the swamp milkweed blossom, but I do prefer seeing a butterfly sitting there instead.