"So, naturalists observe, a flea has smaller fleas that on him prey; and these have smaller still to bite ’em; and so proceed ad infinitum."
- Jonathan Swift

August 30, 2010

August 30 - Oculotrema hippopotami

The hippopotamus is notorious for being one of (if not the most) dangerous large animals of Africa, as they are extremely aggressive and unpredictable, and are responsible for killing more people than some of the iconic predators of Africa such as lions and crocodile. However, even this fierce giant is ailed by a tiny irritant - Oculotrema hippopotami - a species from a group of ectoparasitic flatworms known as the monogeneans.

Most monogeneans live on the skin or gills of fish, however there is an unusual family of monogeneans called the polystomatids that live mostly in the bladder of frogs and turtles. O. hippopotami can be considered even more of an oddball out of a family of oddballs. Not only has it colonised a mammal, it also lives in a peculiar part of its host. As its name implies, it lives in proximity of the hippo's eye, more specifically, under the eyelids. So for all its brazen brawn and strength, the mighty hippo is not immune from being parasitised!

Photo is from this site.

Contributed by Tommy Leung.


  1. what's the pic of?

  2. The pic is the parasite described in this blog post

  3. ...and lives apparently exclusively on the tears of the hippo - incredible specialism which I first read in the excellent Fleas Flukes and Cuckoos and have been quoting ever since. Didn't know much else till now, so thanks.

  4. I found 3 of these things on the floor. I live in Southern Calif. How unusual is this. I stopped my dog from eating them. Whew...

    1. I don't know how you could have possible seen them in Southern California given they are found on an entirely different continent, and are localised entirely under the eyelids of hippopotami.

  5. It’s incredible how many species look alike. For instance, compare this to many helminth commonly found in the US. Without precise equipment and technology that regular people don’t have access to, there’s no way to differentiate what’s what. On top of that, we discover new species every day, find extinct ones still thriving, a whole new BRANCH on the tree of life was just discovered.

    Science and medicine aren’t going to catch up with species introduction, migration, evolution, etc until something catastrophic happens, as always.