The high relevance of host–switching for the diversification of highly host–specific symbionts (i.e., those commonly inhabiting a single host species) demands a better understanding of host–switching dynamics at an ecological scale. Here, DNA metabarcoding was used to study feather mites on passerine birds in Spain, sequencing mtDNA (COI) for 25,540 individual mites (representing 64 species) from 1,130 birds (representing 71 species).