Move towards him and he will scurry back under the board, then come back out after a moment.
Obviously, he is waiting for something to eat to walk by, or fall down from above. But I've never seen it happen.
Day or night, he is always there.
Then, one day, weeks or months later, he is dead and I sweep him up.
Next year, another spider will appear there, and not always the same species, but at the same place.