"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

December 6, 2010

December 6 - Scaphanocephalus expansus

One way to look at parasites is as generalists or specialists. Generalists are non-host specific and while some infect a group of related hosts, others may infect completely unrelated hosts. Specialists infect only one species of host. This strange-looking trematode with wing-like expansions on the anterior end is an intestinal parasite of the osprey, Pandion haliaetus. The osprey is so highly evolved that it is the only species in its own family, Pandionidae. Perhaps because of its evolutionary isolation, the osprey has an unusual number of helminth specialists, and because its diet is 99% fish, almost all of them probably use fish as an intermediate host.

Contributed by Mike Kinsella.


  1. It is interesting to see the diversity of trematodes. It is really cool to see the diversity, when first learning about the group I thought that they would all be very similar in appearance. It is interesting to see the diversity. I also find it interesting how this parasite was able to coevolve and become infective to a particular bird species. There is a lot more than meets the eye with trematodes.

  2. cool to see a parasite that is expansive or has a large spread, would like to know the side effect.