Not extinct but thriving-The rediscovery of the horseshoe bat fly Phthiridium biarticulatum (Diptera: Nycteribiidae) in the United Kingdom.

Bat flies are haematophagous ectoparasites of bats, which have been infrequently studied in the United Kingdom. Phthiridium biarticulatum Hermann (Diptera: Nycteribiidae) is one of three species of bat fly that have been recorded in the United Kingdom. It was last recorded in 1959 and is considered extinct. We report the presence of P. biarticulatum on Lesser Horseshoe Bats Rhinolophus hipposideros (Bechstein) (Chiroptera: Rhinolophidae) at 14 sites across South West England, with a host infestation rate of 17.1% (58/339) of adult bats across 28 surveyed sites with maternity colonies in buildings. Using a species distribution model, we predict range suitability for P. biarticulatum across South West England and Wales. Our findings indicate that P. biarticulatum is not only present in the United Kingdom but may be common across the Lesser Horseshoe Bat's range, highlighting the need for ongoing monitoring of the Nycteribiidae, a neglected group of parasites, given their potential to vector pathogens.