Parasites with low host specificity are predicted to search for hosts in ways less specific than highly host-specific species. They may also be better dispersers. Unionicolan mites that parasitize mussels are positively phototactic, with some species becoming negatively phototactic when host substances are present. This response has been interpreted as an aid to host location and occurs in species where adult mites have a relatively permanent association with hosts. Three species of Unionicola (Unionicolidae: Acari) that differ in host specificity co-occur in freshwater mussels (Unionidae) in St Mark's River in north Florida.
