The Elanthia beetles were small insects that featured in the BBC show Merlin.
Edwin possessed a small box containing Elanthia beetles with which he used to poison Morgana in order to heal her and gain the favor of Uther Pendragon. Once gaining the kings trust, he used the beetles on Uther to gain revenge for the death of his parents however he was killed by Merlin who used his magic to remove the beetles without Uther discovering his magical origins.
The beetles were magical which were smaller then a Human finger. and required a special word to come alive. Once awakened, they were capable of being placed near a person whereupon they entered the brain leaving the individual in a coma-like state. There, they began to devour the soul of the person and eventually led to their death. However, a person with magic was capable of bringing the beetle out and turning it back into its unliving state or killing it.