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.
The following pages show more examples of parasites that spread by controlling their hosts.
Image: Michael Grove
Brandon is a Wired Science reporter and freelance journalist. Based in Brooklyn, New York and Bangor, Maine, he's fascinated with science, culture, history and nature. Follow @9brandon on Twitter.