Association of Leeches with the Endangered Houston Toad

The prevalence of leech attachment on anuran taxa is largely uncharacterized. When parasitic, such relationships may regulate amphibian populations and function as an obstacle to the recovery of imperiled species. We evaluated the prevalence of leech attachment in a population of endangered Bufo (= Anaxyrus) houstonensis (Houston Toad) in Bastrop County, TX, during the spring of 2021. Of 191 toads examined, 2 (1%) were each infested with a single leech. Molecular analysis of the cytochrome c oxidase subunit I gene identified 1 of those leeches as Helobdella austinensis. This constitutes the first reported association of H. austinensis with a vertebrate host and extends the known range of H. austinensis similar to 50 km eastward. Leech attachment in this Houston Toad population is rare and the nature of the association remains unclear.