Advanced Civilization in the Delta Quadrant. Their bodies release a
pheromone that blocks long term memory engrams in other species. They
are fearful of contact with other worlds and they do not allow anyone to
leave their society.
Advanced Civilization in the Alpha Quadrant. Took over the Federation
starship, USS Prometheus, the Doctor over came them to return the ship
to Starfleet's hands.
'Message In A Bottle'