Saturday, December 27, 2008

This Weeks Sci-Fi Worthy Parasite

One of the largest groups of parasites, the trematodes, have all kinds of strategies to trasmit between hosts. The genus Microphallus causes its hosts like shrimp, to swim upwards or otherwise endanger themselves so that they are eaten by the parasites next host - birds.

Dicrocoelium dendriticum

Sure, it looks harmless.

But perhaps the coolest trematode is Dicrocoelium dendriticum. It has a very unusual lifecycle, which is between grazing animals like sheep, snails, and ants. The adults in the sheep's liver reproduce and shed eggs into the feces. The eggs are then picked up by snails, which apparently are fairly fond of eating sheep poo. The larvae then hatch and multiply, finally leaving the snail as little slimy balls that are irresistible to ants.

Dicrocoelium dendriticum

The Life Cycle

But then, you might ask, how does it get from ant back into sheep? Sheep don't eat ants, and ants don't tend to interact with sheep. So the fluke manipulates the ant's brain in a superb form of body-snatching. At night, infected ants climb to the top of grass blades and bite down, waiting. If they're eaten by a sheep, great, if not, in the morning the ant climbs down and resumes its normal activities, only to return to the grass blades at night. Because the ant (and thus the parasite) wouldn't survive all day in the sun, the parasite selectively controls the ants behavior only at night.

If you aren't totally amazed by the precision of this behavior, you should be. Imagine if we had such precise control of someone's neurons and behavior! It's a sci-fi dream come true. Luckily, it doesn't infect our brains...


Anonymous said...

I love that drawing. :D

Also, the parasites are called "microphallus"? Little penis? How on Earth did they get that name?

Mason Posner said...

The behavior modifying parasites are truly cool. Have you written about Toxoplasma and its effects on fear in mice - so they get eaten by cats?
I came across your blog on the Research Blogging site and noticed that you just started posting there. I have a relatively new science blog myself and am getting some good tips by reading yours. Keep up the good work!

Cunning_Linguist said...

Is this the spot where I make comments about the ex wife? It's a parasite post, yes? :P

I'm with ranka.... maybe they're angry because they have tiny weiners or sumthin.

Christie Lynn said...

You know, I *tried* not to mention the whole little penis bit. I *tried* to be a little more mature than that. I should have known better.

The Science Pundit said...


I have to say that this gives a whole new meaning to the phrase "thinking with one's penis".

Mark said...

I completely understand the fascination with parasites!, While reading this post, I started to wonder about how lucky we really are that we're not infected. Considering that parasites appears capable of the most extreme behavioural changes, shouldn't we try to see odd (human) behaviour in a different light? Maybe wonder which parasite is gaining...