MS. REBECCA SHEIR
We move now from mysterious creatures many of us chase to mysterious creatures most of us want to avoid like the plague. We're talking parasites, specifically parasites that turn their hosts into zombies. Zombie-fication, it turns out, isn't all that unusual in the animal kingdom. And right here in our region, we recently saw a mysterious example of this mind-controlling behavior among insects.
MS. REBECCA SHEIR
Environment reporter Sabri Ben-Achour went out on the trail of some teeny-tiny zombies to find out more,. Oh and a few parts of this story might not be for the faint of heart and/or the weak of stomach, I'm just saying.
MR. SABRI BEN-ACHOUR
Earlier this year, something very, very strange happened to millions and millions of flies in our area.
MR. MIKE RAUPP
We were getting literally hundreds of reports of these crazy, dead flies everywhere on vegetation, on signposts and people simply wanted to know what was up with these dead flies.
Mike Raupp is an entomologist at the University of Maryland.
Now, this is a pretty crazy story.
The flies, they're called seed corn maggots, were attacked by fungal spores.
A kind of fungus called entermoptera (sp?) .
And not just any spores, but -- and I am not kidding you with this, mind-controlling spores.
It basically zombie-izes them. In other words, it manipulates their behavior so rather than flying, the fly is now walking to a high point, let's say the tip of a blade of grass, the turn of a leaf.
And when it's way high up, the fungus explodes out of the body and spews its spores into the wind.
This high vantage point, in other words, gives the fungus exactly what it needs in terms of finding a new host.
Does any of this sound familiar? Maybe because there's an entire genre of horror films based on this exact idea of mind controlling parasites and zombies.
UNIDENTIFIED MAN 1
You see their young enter through the ears.
UNIDENTIFIED MAN 2
Now Brian's acting a little peculiar.
UNIDENTIFIED MAN 3
He's like a completely different person. I don't even know him anymore.
UNIDENTIFIED MAN 4
"Slither," they came from within, brain damage, "Invasion of the Body Snatchers"...
The list just goes on and on and on. But you know what? Here's a horror film for you. It's called reality. It's actually a video from a lab in France and it's playing on screen on this laptop.
UNIDENTIFIED MAN 5
That's just wrong, that's nasty.
Giant worms are exploding out of a cricket that's floating in a swimming pool. This is another example of a parasite-modifying host behavior.
It turns out there are small organisms called hairworms. They begin to reach maturity inside the cricket. They increase its activity level and they make this behavior become very erratic. Crickets that would normally kind of move pretty slowly and stay in dimly-lit areas actually become attracted to light. What this does is bring them out of their normal habitat and increase the likelihood they're going to jump into a pond.
Under the moon, ponds and lakes look like portals of light.
Once they reach the edge of that water, they take the suicidal plunge into the water and this is the point at which the hairworm will emerge from its host, swim out into the water, find a mate, reproduce and lay eggs and complete the lifecycle.
Mind-controlling parasites are all around us. The number of creatures that can be affected by them is...
MS. JANICE MOORE
Oh, it's huge. I think probably every animal can be affected.
Janice Moore is a professor at Colorado State University and she wrote the book on parasites and animal behavior.
I think that most parasites have an effect on host behavior. In the crudest sense, if they simply make a host sick, it's going to behave differently. But in fact, most parasites, I believe, do something to the host's behavior, such that a host plus a parasite is simply not the same organism as the host by itself.
Often it's because a parasite needs to get to some final destination, sometimes this means it needs to hitch a ride on a prey animal. There are parasites that make fish more careless so they get eaten by birds or make shy bugs search out backgrounds where they stand out more to predators. But how are they doing this?
There are many, many mechanisms that can result in a changed behavior and if you take the world of parasites broadly, we don't know the half of it yet.
Moore says they can simply sap energy from the host and make it hungrier. They can interfere with hormones or they can pump out their own neurotransmitters and some can be exquisitely precise. Take toxoplasma gondii for example. It's a protozoan with its own gene for making the neurotransmitter dopamine.
Toxoplasma basically makes rodents somewhat fearless around cats. In fact, it's even more than fearless. There is some evidence that they're actually attracted to the smell of cats and the cat urine.
Yes. The rats seek out cat urine and just cat urine, not horse, not cow urine. And a rat that likes cat urine is probably more likely to get eaten by a cat.
And cats are the final host, the animal where toxoplasma can actually undergo a sexual reproduction (word?) . It's really remarkable.
Given all of these examples, could we ever be controlled by parasites? Bob Yolken is the chair of pediatric neurovirology at Johns Hopkins Medical School.
DR. ROBERT YOLKEN
In really many studies around the world, individuals that have schizophrenia or bipolar disorder have a higher read of being exposed to toxoplasma than individuals who don't. And with about a two or two and half fold increased odds.
There are three studies I know of now suggesting that suicide in humans, in largely young adults is associated with increased rate of toxoplasma.
And remember how some hosts become fearless?
Additional studies have looked at accidents, individuals in automobile accidents, both actually drivers and pedestrians, and they have increased rates of toxoplasma as well.
Cause and effect are not proven here, but wouldn't that just be quite the coincidence otherwise. So does this complicate our notion of free will? Maybe, says Moore.
I do think about free will some because I do think about how we're all trapped in our own skins. Humans are really gifted with big brains and with long lives and so we can learn a lot and we don’t have to be trapped by genetics as much as animals that live for three days. But at the same time, we're still somewhat limited. And to tell you the truth, free will, in general, it always amazes me how, in the same situation, some people will rise to the occasion and be saints and other people will be sinners.
A lot of things affect that, Moore says, but we may have to add parasites to the list. I'm Sabri Ben-Achour.
To see pictures, videos and studies from this weird and wild world of mind-controlling parasites, visit our website, metroconnection.org
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