The tiny freeloaders may be considered disgusting by many but new research shows they are crucial in shaping ecosystems
The leech craze of the 1800s put parasites on the map. Collectors (usually women and sometimes old horses) would stand in ponds waiting for medicinal leeches to come and suck their blood. They were then picked off and sold for bloodletting.
The parasites were so popular that by the early 1900s they were nearly extinct, and there was a coordinated effort to save them. Even so, the European medicinal leech, Hirudo medicinalis, has been labelled as near threatened on the IUCN red list since 1996, and remains one of the few parasites with formal protections.