Detoxification of poisonous xenobiotics in animals is typically performed by multi-gene enzyme families. Within arthropods, only insect genomes have been studied in detail where these detoxification families are well characterized. We recently uncovered a new enzyme family in the genome of a non-insect arthropod, the extremely polyphagous plant-feeding spider mite Tetranychus urticae. Phylogenetic analysis showed that this proliferated family was acquired through horizontal gene transfer from a fungal donor. The fungal homologues are known to code for secreted intradiol ring-cleavage dioxygenases that cleave a particular set of complex aromatic structures, commonly found in pesticides and toxic plant metabolites. It is our hypothesis that the acquisition and proliferation of this novel family in plant-feeding spider mites provides a selective advantage by detoxifying both natural and synthetic xenobiotics. This newly discovered genetic repertoire of spider mites is of huge interest for the bioremediation of man-made aromatic environmental pollutants such as PCBs and pesticides. By means of this multi-disciplinary project, we aim to study its precise role in mite (xenobiotic) metabolism and expect to open up avenues to new and exciting biotechnological applications that will extend well beyond agriculture.