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The family name is (in different spellings) 'quaedvlieg' or 'quaedflieg' (also with variation in the use of ae, aa and a). I have not with certainty been able to establish the etymology. According to a Dutch insitute for social studies it has been proposed to be related to 'bad flies' as in flies that transmit desease to cattle, in particular mastitis, which is transmitted by Hydrotaea irritans. It beats me why anyone should want that as a family name...