Geographical distribution of Hirudo medicinalis and H. verbana, based on data published in 2012 (A). In the species H. verbana, a western (w) and an eastern (e) phylogroup has been identified. Occurrence of medicinal leeches in the nest of aquatic birds (B). The photograph shows adult, living specimens of H. medicinalis (with cocoon, see Inset) collected from a nest of a water bird (western marsh harrier, Circus aeruginosus) in Poland (adapted from Kovalenko and Utevsky 2012 [A] and Buczyńsky et al. 2014 [B], respectively).