Zombies have taken many forms in popular culture. In Michael Jackson's "Thriller" music video, corpses climb out of their graves and perform an impressively coordinated dance. In HBO's "The Last of Us," a fungus infects humans, takes over their bodies and turns them into hosts that help spread the infection. Even Plankton has tried his hand at taking control of another organism in "SpongeBob SquarePants."

These examples are fictional, but they all play with the same unsettling idea: Can one organism take control of another, even after death? In nature, the answer is not quite as dramatic, but some parasites and fungi come surprisingly close.

I spend much of my time as a biomedical engineer and synthetic biologist thinking about how biological systems sense signals, process information and change their behavior. That is part of what makes the idea of one organism taking control of another so fascinating to me.

Some parasites and fungi can alter the behavior of a living host in ways that benefit the parasite. They do not bring the dead back to life. Instead, they interfere with biological systems that control movement, motivation and decision-making.

Zombie ants and fungi
The best-known example of a parasite changing its host's behavior is the "zombie ant" fungus, Ophiocordyceps, which helped inspire "The Last of Us."

The life cycle of the zombie ant fungus begins when fungal spores land on an ant. The spores stick to the ant's outer surface and eventually break through it, allowing the fungus to enter the body. Once inside, the fungus grows and spreads while the ant is still alive. The infection can develop over several weeks before the most dramatic changes in the ant's behavior begin.

Eventually, the infected ant leaves the colony and begins wandering and climbing vegetation. This behavior moves the ant away from its normal habitat and into a location that favors fungal reproduction and dispersal. Near the end of the infection, the ant bites tightly onto a leaf, twig or other plant surface and remains attached in what researchers call a death grip.

After the ant dies, the fungus consumes the remaining tissues and produces a stalk from the ant's body. This structure releases spores that can fall on other ants below and begin the cycle again.

How does the fungus make the ant do this? You might imagine fungal cells invading the ant's brain and taking control. Surprisingly, researchers examining infected ants before death found extensive fungal growth throughout the body and around muscle fibers, but not inside the brain. Fungal cells can form networks around the ant's muscles, suggesting that the ability to manipulate behavior may involve communication between the fungus and multiple host tissues rather than direct control of the brain...