Without a doubt those are from bark beetle larvae eating through the wood. I see it all the time when I chop wood during the winter months. If you Google image search "bark beetle tracks" you will find many examples. Some of the designs that are created can actually be quite intricate and almost art-like. Unfortunately, the beetles are devastating the trees out here in California and are killing off many of them.
Kinda like they forget a spot and go over it once more or perhaps it was good stuff, its bark beetles in wet weather earth worms do then the same thing under rocks.