Passive Dispersal of Four Species of Freshwater Leeches (Hirudinoidea) by Ducks

The passive transfer by ducks of two parasitic sanguivorous species (Theromyzon rude and Placobdella papillifera) and two predatory species (Helobdella stagnalis and Nephelopsis obscura) of freshwater leeches was examined experimentally using both adults and cocoons. T. rude adults were transferred both in the nares, while feeding, and also on the duck's body. P. papillifera were transferred at a lower rate on the duck's body only, while H. stagnalis and N. obscura were not transported at all. Ingested adults were not recovered from the faeces of the ducks, but viable N. obscura cocoons were recovered from the faeces of fed ducks. It is concluded that passive transport by birds is probable for the parasitic sanguivorous species and those leeches which attach their cocoons to macrophytes. The evidence does not support the proposal of passive dispersal by ducks for H. stagnalis, a predatory Glossiphoniidae, despite its cosmopolitan distribution.