A nest built on top of a painting is probably younger than the painting, but a nest covered over with pigment is probably older than the painting. At one site, ancient people had painted a figure over the remains of one nest, and some time later, wasps built two more mud nests atop the painting. Radiocarbon dating those nests suggested that the painting is 11,300 to 13,000 years old. – Ars Technica