It sounds like the plot of a horror movie: In the dead of night, a parasite invades a victim’s body. Over the next few days, the parasite steals nutrients from it’s/its unlucky host and grows stronger. As the host weakens, the parasite finds a way to control the host’s behavior.

Believe it or not, this can actually happen. Some organisms, called parasites, do sometimes take over creatures’ brains, turning them into zombies. Check out these creepy examples.

A wasp lays an egg inside an unsuspecting ladybug. It also injects the bug with a virus. When the egg hatches, the wasp larva bursts out of the ladybug and spins a cocoon under the bug’s body. Meanwhile, the virus kicks in, causing the ladybug’s shell to twitch. That’s great for the larva—the twitching scares away it’s/its predators—but it’s/its not so great for the ladybug, which is no longer able to move. It’s/Its essentially been turned into a zombie bodyguard.

A certain kind of flatworm is known for it’s/its sneaky—and totally disgusting—mind-control trick. First, a garden snail eats bird droppings infested with a flatworm’s eggs. After hatching inside the snail, the worms crawl into the snail’s eyestalks, causing them to swell. Scientists believe the worm then releases a chemical that convinces the snail to travel to wide-open areas, where birds mistake the snail’s wriggling eyes for caterpillars. The birds gobble up the worms, the worms lay more eggs, the birds poop out those eggs—and the disturbing cycle starts all over again.

Horsehair worms are easily some of the creepiest crawlies on Earth. If a cricket eats something with a horsehair worm egg on it, the worm hatches and grows—inside the cricket. Since the worm needs water to complete it’s/its life cycle, it pumps out chemicals that force it’s/its host to jump into water. There, the cricket drowns and the worm emerges.