#rhynchobdellida

Helobdella robusta

A freshwater leech from North America that preys on snails.

There's no quite place like home-- no matter how unpleasant it may seem to others. The leech Placobdelloides jaegerskioeldi has one of the most unique homes on earth: the inside of a hippopotamus' anus. Adults reside within the last 10 cm (3.3 in) of the rectum, where they have easy access to their host's blood from the delicate capillaries that flow close to the skin there. Parents will even go so far as to move house with their young; hatchlings attach to their parents underside, and the obliging adult crawls up a host's leg into their anus and deposits their offspring inside for their first meal.

Some leech species are generalists, feeding on just about anything. And others are very, very specific. The duck leech is one such species; adults exclusively attach themselves to the mouth, throat, or nasal passages of ducks. However, they don't feed on their host themselves-- instead, they release a brood of their young so that the next generation will have easy access to their first meal.

Though there is quite a bit of debate about the largest species of leech, the Amazon giant leech is certainly at the top of the running! At up to 45 cm (17.7 in) in length, this species is of particular important to scientists, as it was declared extinct in 1893 and only rediscovered in 1970. Several specimens were caught for captive breeding, and one (dubbed Grandma Moses) managed to produce over 750 offspring!