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This happens to my front step railing every year or so. It's two things that have been mentioned, but in combination.
Carpenter bees bored into your wood to make their nests, and then a woodpecker came along and ate the bees in their nests.
Here's a cool article about the bees. http://entomology.ca.uky.edu/ef611
And that's why every carpenter bee horror story starts with "There was a knock at the door..."
knock knock
Imagine Woody Woodpecker’s laugh being the last thing you heard
This is exactly what it looks like.
I had this exact situation happen to the fascia boards on my previous house. Carpenter bees bored into the wood and were living in it. Then a woodpecker came along and got them.
The damage in your picture looks exactly how my fascia boards looked after the woodpecker got his meal. You can also see the tunnels that go into the wood. I never even knew the bees were in the fascia, but somehow the woodpecker did...