Illustration Friday prompt is beneath. Sometimes there are interesting things lurking beneath tree bark that you don't get a chance to see until the tree is dead.
Bark beetle larvae make these galleries directly under the bark as they feed on the inner bark. The main line that follows the grain is the chamber that eggs are laid in, and the radiating lines are larval feeding tunnels.
The galleries look like fine carving and can be very intricate and attractive, but they're not always a good thing. Generally, bark beetles are important for forest renewal as they attack dead or dying trees, but some are disease vectors and spread things like Dutch Elm Disease.
The galleries are still cool, though.