"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

July 21, 2010

July 21- Pseudocorynosoma constrictum

Pseudocorynosoma constrictum is an acanthocephalan parasite of North American waterfowl. Eggs are released into lakes, where they are ingested by the first host, amphipods. After about a month of development, the infective cystacanth stage is reached and the worm can be transmitted to birds. The cystacanths are bright orange and clearly visible through the cuticle of the intermediate host (see picture). Several acanthocephalan species have orange cystacanths, and there has been much debate about the function of this pigmentation. Hypotheses include increased conspicuousness to final host predators, protection against UV radiation, or that it is just a byproduct of larval physiology.

Contributed by Daniel Benesh.


  1. Can this infect humans? My friend has peed out two of these (at least it appears that way) that we fished out of the toilet. We kept the bigger of the two. Can you tell me more about it?

  2. It sounds like you friend should see a doctor.

    No, this parasite cannot infect humans. Unless you have been scooping out and eating a whole lot of little crustaceans out of a lake somewhere and eating them raw, there's no way for you to encounter this parasite. Even if let's say you have been doing the above, it is a bird parasite and is unlikely to survive in a human body. Also it is a gastrointestinal parasite and does not have anything to do with the urinary tract.

    Keep in mind the photo of the parasite shown above is not even its final form.