ON THE DARK SIDE?: Some tiny organisms can make much larger animals do their dirty work for them. Find out how parasites can take control of bodies and minds.
Image: STEVE YANOVIAK
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A spider, seemingly possessed, spins an uncharacterisitic web—just before wasp larvae nesting on its abdomen suck the last nourishing juices from the spider's dying body and make a cocoon in the weird web.
A worm gets into the brain of a shy, shade-loving snail, compelling it to crawl out of its safe home and into the open where it gets attacked by a bird—which is destined to be the parasite's next host.
Creepy tales like these are happening all over the animal kingdom, and not just on Halloween or under a full moon. Some organisms have taken evolutionary advantage to a whole new level, achieving success by insidiously—and still quite mysteriously—changing the behavior of another animal against its will.
View a Slide Show of Zombie Animals
Although not undead in the strictest sci-fi definition of "zombie," these captive creatures nonetheless behave as if possessed by a force from beyond. That force, however, is often controlling them from the inside, making the unfortunate hosts do deadly things.
In the case of the spooked spider (Plesiometa argyra), a parasitic wasp (Hymenoepimecis argyraphaga) lays her eggs on the spider's abdomen. Just before the larva emerges, the host spins a strange, new type of web—one that looks nothing like its usual wide nets. This silk platform, however, is perfectly suited to supporting a cocoon for the vulnerable young wasp larvae, which have been feasting on the spider's innards as they grow.
The snail-manipulating flatworm (Leucochloridium paradoxum) grows and multiplies inside the snail. Once ready to move on to its next host, the worms push up into the snail's tentacles, making them swell and squirm, mimicking the action of bugs that birds like to eat. As the snail crawls, blindly, into the sunlight, a passing bird is likely to swoop down to snatch a tasty tentacle or two. The worm-infested meal will then infect the bird, which passes it onto other snails via dubious droppings.
The mechanisms by which these parasites are commanding their hosts remain, by in large, unsolved mysteries.
"We don't know how it works, but it's obviously some type of chemical," says David Hughes, a researcher at Harvard University. "It's co-opting a preexisting behavior." As part of their normal routine, snails climb stalks and spiders spin webs, but the parasites have managed to take these particular behaviors and mold them to their own advantage—often resulting in their hosts' demise.
"Typically you have behavior that a host would do at some point in its life," adds Edward Levri, an associate professor of biology at The Pennsylvania State University in Altoona. "It's just happening at an odd, nonadvantageous time for the host, to the benefit of the parasite."
Creepy control
So many very different—and very bizarre—examples of parasite-controlled behavior modification have been observed that researchers have a wealth of instances to study. But it is no longer enough to document these parasites. "We have to go beyond describing behavior," Hughes says. "Now people are trying to look at how parasites are changing behavior."
Figuring this puzzle out, however, has proved to be quite difficult. "Modified organisms are more complex than we had previously believed," says Frederic Thomas, a scientist at the Genetics and Evolution of Infectious Diseases research group in Montpellier, France, and the department of biology at the University of Montreal.
With improved technology, researchers in this freaky field have been able to start sequencing the genomes and parsing proteins of some of these parasites and hosts to unravel where behavioral changes happen. "In at least some cases, some of these parasites produce neurotransmitters or hormones that mimic host hormones," Levri says.
Not all of the parasites, however, are traditional body snatchers.
"You can easily understand that a parasite can control the behavior when it is inside," Thomas says. But how do some manage to dictate a host's behavior when they're not, technically, hosting a parasite? "To me, it's like magic," he adds.
The aberrant web-spinning P. argyra demonstrates this to some extent, the parasitic wasp eggs having been laid on the outside of the spider's body. In another bizarre example of external control, a different species of wasp (Ampulex compressa) is able to control a cockroach—via an injection into its brain—and force it to enter its nest to become food and shelter for the wasp's larvae.
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36 Comments
Add CommentAw you ended it on the part I was afraid of while reading the entire time: what if there's ones that affect us?
Reply | Report Abuse | Link to thisCreepy.
It is call marraige!
Reply | Report Abuse | Link to this"have some of the same effects on humans, who can be infected by ingesting parasite eggs from cat feces"
Reply | Report Abuse | Link to thisUhhhhh....... What?
I would venture to guess that people who eat cat feces already have problems with controlling themselves!
Great story for Halloween! Real science is better than fiction any day.
Reply | Report Abuse | Link to thisCat feces decomposes quickly and can be inhaled. There are a lot of different and equally grotesque viruses and parasites in that dust. That's one of the reasons why pregnant women aren't supposed to clean the cat box. At least, that's the excuse my roommate always gave...
Reply | Report Abuse | Link to thisWho ever thought a sand box in the back yard was a good idea,but there they are.Ring worm and others are alive and well,and its not the cats that got us to build these things?
Reply | Report Abuse | Link to thisSci Am published an article a few years ago about the bacterium toxoplasma, which infects cats and can cause problems for pregnant human mothers. Most interesting is the fact that toxoplasma causes rodents to lose their fear of felines, so they become easy prey for cats. The rodents pick up toxoplasma from feline droppings, thereby completing the circle for the parasite.
Reply | Report Abuse | Link to thisThats awesome...cats controlling our behavior so we build larger litter boxes...lol
Reply | Report Abuse | Link to thisQuite a scary thought to know that such things exist, and even more scary that even scientists have not figured out all the facts yet, much less be in a position to control or do anything about it! Isn't this the information stone age?
Reply | Report Abuse | Link to thisIf u didn't know cat like/have a habit to smell their feces and when that cat come in contact with human(who keeps cats as pets) u know it is more likely to infect human, I really doubt anyone eat cat feces, seriously, just need to think in logical way.
Reply | Report Abuse | Link to thisScientist haven't figured out many things LOL, if they do not know it simply do not exits, recently I read from(i believe a magazine on human behavior) that there is no God, God is just a Quack because there is no way to know if its real or not. We humans believe in God because we just want to go to better place and to create fear in bad people and stop good people to turning bad.
Reply | Report Abuse | Link to thisAt least thats what I read/understood
Dan Dennett has been talking about brain manipulating parasites for years. Religion falls into this category.
Reply | Report Abuse | Link to thisso does gossip
Reply | Report Abuse | Link to thisI wonder if natural drugs such as marijuana, peyote, and mushrooms could be classified as zombifying parasites.
Reply | Report Abuse | Link to thisi will go and get cat ,it might make my wife more berable to live with as she has no moral compunction to be nice to me or any one else, and if it makes me less moral i will be able abandon my vows and go astray wityhout any guilt. did the
Reply | Report Abuse | Link to thisstepford wifes keep cats?
I read a report several years ago about a parasite that caused fish to swim upside-down near the surface, flashing their silvery-white bellies, which attracted the eagles or hawks that ate the fish. The raptors then hosted the parasites. If I recall it, the fish ingested the raptors' excrement, completing the cycle. I can't find the article now.
Reply | Report Abuse | Link to thisPerfect article for Hallowe'en!
Reply | Report Abuse | Link to thisOn another note, who let "by in large" slip by? Editors, please, it's "by and large."
Maui manuscript medic
Dawkin's speculates that this could be an explanation for religion.
Reply | Report Abuse | Link to thisA parasite attacking the human brain.
wow i never knew that
Reply | Report Abuse | Link to thisLooks cool and creepy but how is it a zombie creature thingamobob
Reply | Report Abuse | Link to thisboo i am a vampire
Reply | Report Abuse | Link to thiswierd i think so bye
Reply | Report Abuse | Link to thisSlide show totally creeped me out. Article also attracted a bunch of creepy commenters. Maybe the article is a parasite.
Reply | Report Abuse | Link to thisWe already have plenty of human parasites. They use the government to take from those who produce. Once the host agrees to give a share of production to the parasite, the parasite demands more, until finally the host perishes and the parasite is forced to find another host.
Reply | Report Abuse | Link to thisIn the U.S, we generally call these parasites democrats.
I wish stupidity could be cured by killing a parasit.
Reply | Report Abuse | Link to thisThe worst kind of parasite is a journalist. He just publishes an an article in one the medium he works for and all those who reads it or listens to it starts believing that that's true. And keep reading or listening him so he can keep his job. Another kind of parasite who is very harmful to humans is a religious cleric. Does anybody wonder why they have a living without working at all?
Reply | Report Abuse | Link to thisExcellent insight.
Reply | Report Abuse | Link to thisMaybe we humas ARE the parasite. The planet Earth is our host we use to expand as a species... Off to Mars!
Reply | Report Abuse | Link to thisim am terrified!!! please tell me they do not infect humans!!!
Reply | Report Abuse | Link to thisI'm TERRIFIED!!! Please tell me that they don't infect humans!
Reply | Report Abuse | Link to thisim sure they dont
Reply | Report Abuse | Link to thisYoosdef, are so very close to the factual information. A parasite is the original hacker and has gotten itself into the build of the human and other animals, or in the dna it has set itself to be built in the womb and infused into the host and can appear like simple brain tissue. It is more a leader of the bacteria world and is chemical, plauges and such. It uses the human communications to spread its instructions to the parasites in other people and also uses the same books, to tell the human it’s so called place. You’ll find many illogical statements in religions and it is wrapped around instructions of care or disorder of the host for the parasite to do. Or hybridization. It puts its same instructions in childrens cartoons for the ones who are new and anywhere that is communicable, but it’s system of worship is for its own faster regeneration and can peruse humans to further its goals. Both being the voices of evil and good more known as schizophrenia, but it hides and indirect communication is chemical and direct is literally auditory hallucinations. If it can’t get other hosts to cause trauma for the younger people it will do it itself within the mind. It tries to take the place as the natural instincts of all beings to be the only ones with foresight into the future and distracts the human from using it’s own instincts and they never run from earthquakes or tsunamis as animals do. It has pulled the life of its’ host into itself and removing it will cause the death of the host, but those that are used in its show are more a carrier and it gives up its life to further its whole aims. For the human who are eaiser hacked, sexual disorders to breed in the traits where the parasite is stronger and host weaker. But now it is almost time for the reverse, and “the voices”, will be the television, radio, and the computer extension of the brain, they are already making it past the inflammatory responses and immune system but their attacks must be used wisely lest the hosts immune system attack them. These are the divisions it uses to incite them against one another of their beliefs and world views and typic mispelling as pure accidental. Though it may seem smart, it has no physical survival and blind men read the bumps on the log, its knowledge is a consistent furthering of what the human that is used as its instrument to see the world around it is the one now growing weaker of that the parasite, lord of the flies and creator of plauges, mostly an exaggeration to appear larger, object may appear closer than they are behind you. The balance system is almost fulfilled now, hence the parasite will be the “power” of the future, one with a negative terminal and one with a positive terminal and it will charge the houses and generate electricity; but what of its future, 11 one on the high end and one on the low end, it must live in its own delusion online and will be removed one day, and stuffed into the commodity boxes for resale, and 10 will be forbidden access to the human brain system, what of the words to be a more structered solidification of atomic and smaller worlds as they harden, and even down to yatto, where the buffalo roams and the seminole blows, they will all join in…
Reply | Report Abuse | Link to thisToxoplasma gondii is a parasitic protozoa. Check it out, fascinating stuff, said to desensitize rats, an intermediate host, to cats, its primary host.
Reply | Report Abuse | Link to thisYou wonder if this kind of thing can affect humans?
Reply | Report Abuse | Link to thisGoogle "toxoplasmosis, world cup"
Let me guess; You think Ann Coulter is brilliant with great political insight.
Reply | Report Abuse | Link to thisThat's wrong. We call the parasitic humans "priests".
Reply | Report Abuse | Link to this