How do parasites manipulate their hosts' behavior?

The answer

Parasitic manipulation of host behavior is astonishingly common and diverse. The fungus Ophiocordyceps unilateralis infects carpenter ants and compels them to climb to a specific height and bite down on a leaf vein before dying, positioning the fungus perfectly to release spores. Toxoplasma gondii makes infected rodents lose their fear of cats, increasing the chance of being eaten so the parasite can reproduce in the cat's gut. The parasitic wasp Glyptapanteles lays eggs inside caterpillars; after the larvae emerge, the caterpillar guards the wasp cocoons instead of feeding, effectively becoming a zombie bodyguard. These examples illustrate the extraordinary evolutionary arms race between parasites and their hosts.