Monday, August 27, 2007

Zombie Ants from Outer Space

I promised myself that I wouldn’t do another post with a biological example of the viral model so soon, but Mike the Boyfriend (my sister’s boyfriend, not mine) just told me about this and it’s too cool to delay.

Ok, I admit it, the heading’s a tad misleading: the ant isn’t actually undead, nor is it from outer space. But “Dicrocoelium dendriticum” just wasn’t a very compelling title.

Anyway, there’s a parasite out there that can sneak inside the still-living body of an ant; take control of it; and force it to behave in a suicidal manner. The parasite is called a Lancet Fluke, and it sure jumps through some hoops in order to achieve its purpose; a wonderful example of very specialized adaptation.

The Fluke’s ultimate target is the belly of a herbivore such as a cow or sheep.

This is how it gets there:

Thousands of fluke larvae snuggle into a nice big pile of herbivore poop*
A snail comes along and eats the poop (accidentally ingesting a bunch of fluke larvae).
The snail wanders around, leaving a trail of ooze riddled with now-juvenile flukes.
An ant comes along and eats the snail-ooze. No, really!**
When it eats the snail-ooze, the ant unwittingly eats hundreds of juvenile flukes.
One lucky fluke navigates inside the ant to its brain, nestling in to the area that controls movement and mandibles:

  • While the temperature is warm – daytime – the fluke does nothing. This allows the ant to act normally during the day when all the other ants are active.
  • When the temperature drops below 10C – nightfall – the fluke takes over. It makes the ant climb a blade of grass and latch onto it with its mandibles. The ant remains suspended from the grass all night.

  • When the temperature rises above 10C again – daytime – the fluke relaxes control and the ant resumes its normal activity.

This cycle continues until a herbivore who is out for a stroll one evening happens to eat the blade of grass – ant, flukes and all.
The herbivore digests the hapless ant, releasing the flukes who spread out into its stomach where they can meet like-minded individuals.
Pairs of the now-adult flukes perform a special hug which results in the creation of a fluke egg.
The unlucky host of the party stops eating; it weakens and eventually dies. But before passing on, the herbivore – you guessed it – poops out the fluke eggs, taking us all the way back to step 1.

As I mentioned up top, this is another example of the viral model:

The fluke spreads to ever more sites by hitching a ride on snails then herbivores then snails etc, occasionally getting carried by one of them to a new place it's never been before.

I know this whole process sounds like it comes from a bad ’60’s movie, but it’s real and actually pretty neat. Makes you wonder, how on earth did the fluke evolve in such a specialized manner..?

...And are there any other mind-controlling parasites out there? (Hint: yes.)

(I learned most of this from and some of it from Behavioral and Morphological Changes in Carpenter Ants Harboring Dicrocoeliid Metacercariae, Carney 1969.)

* I’m sorry that 2 out of 3 posts involve the wonders of poop as a transport mechanism. I’m not obsessed with the idea; apparently excrement is just far more useful to the parasites of the world then I ever knew***!

** If you think eating snail-ooze is gross, then why didn’t you complain about the part where the snail ate the herbivore crap?? Maybe you’re just more open-minded than I…although I think that this would show rather conclusively that open-minded people contain fluke worms…

*** By the way, this is why you’re supposed to wash your hands after going to the bathroom! Who knows, if too many people ignore this rule, maybe a similar parasite will evolve that causes people to leave the norms of human society and stay up all night consuming grass…Wait a second: are we too late?? Is it
already among us…?

(picture found randomly at

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