The Ceti Eels In "Star Trek II: The Wrath Of Khan"...

They crawl inside the ear and, ~ Oh, GASP!!!... REAAALLLY GROSSSSSSSSSSSSSS!!!!!!!... :O >>> "Allow me to introduce you to Ceti Alpha V's only remaining indigenous lifeform." – Khan Noonien Singh, 2285 (Star Trek II: The Wrath of Khan) >>> The Ceti eel was a burrowing desert animal native to the planet Ceti Alpha V. Capable of surviving extremes in its environment, the Ceti eel was the only known indigenous creature that survived the orbital shift of Ceti Alpha V following the explosion of Ceti Alpha VI. Ceti eels incubated their larvae within the plates of their jointed carapace. Once emerged, an eel larva could enter the ear of a larger animal, where it wrapped itself around the cerebral cortex. The effect caused the host extreme pain and rendered them extremely susceptible to outside suggestion. Over time, as the larva matured, the subject suffered from madness and eventual death. Twenty of Khan Noonien Singh's followers were killed by Ceti eels in this fashion, including his "beloved wife." (Star Trek II: The Wrath of Khan)