In this video, you see Cordyceps are ‘killer fungi’ that infect ants and other insects, changing their behaviour and eventually killing them. Then a fungus grows out of their body and heads. They have been dubbed ’zombifying fungi’.
A study published in Science and recounted in the Huff Post shows that some caterpillars are susceptible to a virus that:
literally takes control of their brains and makes them climb to the the treetops, where their bodies liquify and rain down to the ground. The method virtually ensures that the virus continues to thrive as it comes down to Earth.
This process is colloquially referred to as the “zombifying effect”.
Then there are zombie bees. A parasitic fly (Parasitic Phorid Fly Apocephalus Borealis) lays eggs inside honey bees which cause the bees to walk in circles, pursue bright lights, makes them unable to stand, and eventually die.
You can add zombie snails to the list. From the Zombie Research Network.:
Worm eggs unknowingly ingested by the Amber Snail hatch in the snails digestive track. The larva then change into sporocysts, causing drastic mutations in the snail’s brain and physiology. Healthy snails seek darkness to hide from predators, but the infected Amber Snail moves itself into dangerous open space and light. It is also helpless to retract its newly swollen, pulsating tentacles.
The end result is that feeding birds mistake the exposed tentacles for a caterpillar or grub, and rip them off the snail’s defenseless head. The flatworm then grows to maturity inside the bird, laying eggs that are released in droppings for new snails to consume. Here’s a clip of the zombie snail in action.
The Other Sociologist 