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The Occurrence of Theromyzon rude (Annelida: Hirudinea) in Association with Mortality of Trumpeter Swan Cygnets (Cygnus buccinator)

Parasitism by nasal leeches has been reported in a variety of species of waterfowl in North America (Trauger and Bartonek, 1977, Wildfowl 28: 143-152). Theromyzon, also known as the duck leech, is the only glossiphoniid leech that feeds while attached directly to the mucosal lining of the nasal passages and/or beneath the nictitating membrane of the eyes of its avian hosts. Theromyzon rude (Baird) is the species reported most frequently from North American waterfowl (Trauger and Bartonek, 1977, op. cit.; Davies and Wilkialis, 1980, Can. J. Zool. 58: 913-916; Davies, 1984, Can. J. Zool. 62: 589-593). Klemm (1982, U S . Environmental Protection Agency Report No. 600/3-82-025, Cincinnati, Ohio, 177 pp.) has reported Theromyzon biannulatum and T . tessuZatum from lakes and ponds in the United States and Canada. Theromyzon feeds on blood and because of its large size (up to 35 mm when blood engorged) and nasal feeding site, it creates some unique problems for its host while feeding. Large numbers of engorged leeches can physically obstruct the nasal passages, pharynx, and trachea, eventually leading to suffocation, particularly in cygnets and ducklings. Secondary bacterial infections may also occur in association with severe infestations. Seven trumpeter swan cygnets found dead at Yellowstone National Park in 1979 and 1980 were frozen and sent to the National Wildlife Health Laboratory for ne-