They are not culturally productive in their hidden fastnesses. Their games, culture, artifacts, and practices are cribbed from the larger muggle culture - suitably modified, of course, to reflect their peculiar abilities. In short, culturally speaking, they are parasites. One suspects that they are economic parasites as well, leaching off the muggle world. One would expect them to be - they have the slaveholding mentality - but there is not enough evidence in the extant narratives from which to make a judgement.
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