Witch Hunter Robin

The STN-J is called in by the local police when a dried corpse is found. When Robin finds a dead insect on the body the team goes on a hunt for a Witch who can control insects. They find that there were two previous victims found in the same condition. The cases point to a similar rash of deaths leading back hundreds of years. Apparently, all the dead are Witches. Is the STN-J dealing with an immortal who feeds on Witches?