Gallery: Attacks of the Brain-Controlling Parasites
01climbing-caterpillars
Once upon a time, parasites were thought to live relatively simple lives: They hitched a ride on a host, sapping nutrients and energy but otherwise leaving it alone. But that was only part of the story. Many parasites actually take control, causing their hosts to act in self-destructive ways that further their invaders' interests. The *Lymantria dispar* baculovirus, for example, causes caterpillars to climb into treetops rather than hiding in bark. When those that go uneaten by birds finally die and decompose (as pictured above), viral particles rain onto foliage below, infecting a new generation of caterpillars. "I think the reason people are a little creeped out by seeing pathogens control behavior is that we have examples of it around us all the time," said chemical ecologist Kelli Hoover of Pennsylvania State University, who describes *L. dispar*'s gene target [in a Sept. 9 *Science* study](https://www.sciencemag.org/content/333/6048/1401.abstract). The following pages show more examples of parasites that spread by controlling their hosts. __Above:__ Dissolving, Baculovirus-Infected Monarch Caterpillar ----------------------------------------------------- *Image: Michael Grove*
02ant-berries
Ant Berries ----------- When the roundworm *Myrmeconema neotropicum* infects giant *Cephalotes atracus* ants, the ants' abdomens swell and turn bright red, causing them to resemble berries. Because the South and Central American forest homes of *Cephalotes* abound with berry-loving birds, it's bad news for the ants -- but looking like a berry is just the beginning. The worms also make the ants sluggish and prone to waving their abdomens in the air, practically inviting birds to eat them. Afterwards, *M. neotropicum* spreads in the birds' droppings. *Image: Steve Yanoviak, University of Arkansas at Little Rock*
03zombie-ants
Zombie Ants ----------- The *Ophiocordyceps* fungus releases a chemical related to LSD, causing infected worker ants to leave their nests and find a leaf about 10 inches off the ground. Once there, the ants attach themselves to the leaf's side, then die. Over the next year, *Ophiocordyceps* consumes their bodies and uses them as a launching site for spores. *Image:* Ophiocordyceps *grow from a dead ant's head. (David Hughes, Pennsylvania State University)*
04suicidal-grasshoppers
Suicidal Grasshoppers --------------------- Once established inside a grasshopper, *Spinochordodes tellinii* hairworms produce chemicals that disrupt their host's central nervous system, causing it to plunge into water. The worms emerge to complete their life cycle. The grasshopper drowns. *Image: After a grasshopper jumps into a pool, a hairworm leaves its body. (VB Films/CNRS Images Media)*
05webs-for-wasps
Webs for Wasps -------------- Wasps are famous for laying eggs in insects that become living meals for their ravenous larvae. *Hymenoepimecis* wasps take it one step further: On the very evening that the larval wasp will kill its orb-spider host, it causes the spider to make a new type of web. Instead of spinning an elegant skein of concentric circles, the spider makes a structure capable of supporting the cocoon that the larva will build a few hours later, after killing and eating the spider. *Image: At left, a regular orb spider web; at right, a wasp-influenced web. (William Eberhard/Smithsonian Institution)*
06risky-fish
Risk-Taking Fish ---------------- Commonly found in North American lakes and streams, *Clinostomum marginatum* -- better known as yellow grubs -- lay their eggs inside fish-eating birds. The eggs are deposited via feces into water and picked up by fish, in whom the parasites mature. When enough grubs have occupied a fish, they make it swim closer to the water's surface. There it's more likely to be eaten, allowing the cycle to continue. *Image: U.S. Fish and Wildlife Service*
07rats-who-love-cats
Rats Who Love Cats ------------------ One of the rare mammalian examples of host-controlling parasites involves *Toxoplasma gondii*, a protozoa that can live in any warm-blooded animal but only reproduces inside cats. Rats infected by *T. gondii* not only lose their instinctive fear of cats, but actually [become sexually aroused by them](http://www.plosone.org/article/info%3Adoi%2F10.1371%2Fjournal.pone.0023277 ). An open question is what *T. gondii*, which alters host behavior by influencing production of the neurotransmitter dopamine, might do in human brains. About one-third of all people are infected, and researchers have linked it to increased risks of schizophrenia and obsessive compulsive disorder. No studies have yet examined how people infected by *T. gondii* respond to cats. [](http://stag-komodo.wired.com/images_blogs/wiredscience/2011/09/kathrdr.jpg) *Images: 1) [tlindenbaum](https://secure.flickr.com/photos/lindenbaum/330136732/ )/Flickr 2) [David Carroll](https://secure.flickr.com/photos/david_carroll/2378065423/)/Flickr*
