The Psycrabs of Metaus

the Psycrabs of the marshes of Metaus have developed an interesting psychic defense
They project a field that retards intelligence to a direct ratio of how intelligent the victim is
In other words,
the smarter you are
the dumber you become
the crabs being nearly mindless are unaffected by their field
and often dine upon the drooling idiots
who were once geniuses