I naively believed that leeches somehow disappeared from the environment when their medicinal use fell out of fashion* in the 19th century; I was sad to discover that I was mistaken.
This 5-inch-long specimen, Macrobdella decora, the North American medicinal leech, was nosing around the spot where the BCs were swimming yesterday. None of us donated any blood this time, but my enthusiasm for skinny dipping in this otherwise lovely pond has diminished considerably.
* It seems that leeches are experiencing something of a revival in contemporary medicine, e.g. https://www.ncbi.nlm.nih.gov/pubmed/7263055, https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3757849/, and https://www.ncbi.nlm.nih.gov/pubmed/7263055.