"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 10, 2010

August 10 - Dicrocoelium dendriticum

Dicrocoelium dendriticum, better known as the lancet fluke, is a species of fluke that lives in the liver of grazing mammals such as sheep. Like most flukes, it has a 3 host life-cycle, the adult worm living inside the sheep, lay eggs which are shed into the environment with the sheep's faeces. The first intermediate host for this parasite are terrestrial snails which become infected by accidentally ingesting the parasite's eggs. The parasite undergoes clonal replication inside the snail, producing hundreds of infective larvae which are then packaged into slime balls and extruded into the environment. For some reason, these slimeballs are eagerly gobbled up by ants which are the parasite's second intermediate host.

Now sheep are not known for including ants as a significant part of their diet, so how is D. dendriticum supposed to get itself into a sheep through an ant? It does that by taking control and setting its ant host up for a rendezvous every evening. Once infected, the ant begins to behave very oddly indeed. As dusk falls, it would crawl up a blade of grass until it reaches the tip, then firmly clamps itself into that position with its mandible for the entire evening. The infected ant would perform this peculiar routine every night, but as the sun rises, it would resume its usual activities - assuming that it has survived the evening and not been incidentally ingested by a hungry sheep. By inducing this peculiar behavioural pattern in the ant host, D. dendriticum brings itself (through the ant) within the vicinity of a grazing sheep, thus setting up an encounter which otherwise would not have occurred, allowing it to complete its seemingly obtruse life-cycle.

Check out the very funny cartoon version of this life cycle here.

Contributed by Tommy Leung and thanks to Craig Carlough (Lancaster, PA) for sending along the Oatmeal comic.


  1. Indeed, the cartoon was pretty darn awesome.

  2. what sort of mechanism does the parasite use to infect the ant? If it's just chemical do we know what chemical or cocktail of chemicals does this?

  3. Do you mean how the parasite is able to manipulate the ant's behavior?

  4. I'm not sure if that's the question Optics Guy is asking, but:

    At the moment, no one knows exactly how the parasite is able to manipulate the behaviour of the ant in such a precise manner. When an ant gobbles up a slimeball, it swallows a clump of 50-100 parasites - all of them genetically identical clones (similar to Galactosomum bearupi - July 28). Most of these parasite migrate to the ant's gaster (abdomen) and encyst there. However, one lone individual will make its way to the head of the ant and settle in the ant's brain.

    What it gets up to in there is anyone's guess at the moment. However, judging from what we know about other host-manipulating trematodes, it is possible that the "manipulator" in the ant's brain is disrupting the ant's usual behavioural repertoire either by secrete some kind of neuroactive chemical, or by inducing some kind of cellular reaction from the host.

  5. Here's another comic about this fascinating parasite:

  6. Hi
    Do you possibly have the first description of Dicrocoelium dendriticum?
    I need to compare measurements of an article.


  7. The species was first described by Rudolphi in 1819 and revised by Looss in 1899.

  8. Hi
    Yes i know,
    but do you have those articles?
    I need to see the first descriptions measurements.
    I will be thankful if you can help me to have a pdf copy of those two articles.


  9. No, sorry, I do not. Perhaps your library could assist you with obtaining them. That said, given the time of publication, I would speculate that you may not find any measurements in them at all. You might find this Otranto et al. (2007) paper helpful, though. (doi: 10.1016/j.actatropica.2007.07.008)

  10. Hi
    I am in a research visit for a short period so cant ask the library.
    But thank you so much for introducing me that article.


  11. if slime balls are eaten by a man can he behave like ant?

  12. No. That stage of the parasite can only infect ants, it does not have the necessary adaptation to infect anything else. If a human eats one of those slime balls, the slime ball will just get digested.