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Just a guess (since there aren't any other guesses posted) (also, I am not in any way a professional who might know for sure) ... But it looks like either one of those tent caterpillar things - they make those big communal webs in trees and can devestate the foliage - or a gypsy moth caterpillar. Which also ruin trees, but mostly stick to oaks.
That's what it looks like to me, but it all falls apart if you don't have trees nearby that it could have come from...