Those markings on the firewood are wood borer galleries.
They are packed with fine waste material called "frass".
This little larva was lurking in on of those frass filled galleries.
These beetle larvae were under the bark as well.
Nasty looking mandibles, eh? This larva probably eats the fungus permeated wood I found it in.
a 10x hand lens.
This is just a sampling of the many insects residing in - and under - the bark of a piece of my firewood. That is plenty to think about as I "fry the frass".