Star Trek: 10 Alien Races That Only Appeared Once
1. Swarm
Built as a potential new Big Bad for Voyager, the Swarm offered up all the mystery and danger that the audience would want from a brand spanking new race. Their ships attacked en masse, forcing Voyager to flee or face certain defeat.
Now this was something viewers would see again with more destructive power through Krall's fighters in Star Trek Beyond.
The Swarm could well have taken a prime spot in the list of enemies Voyager encountered in the Delta Quadrant but they were left swiftly in its wake. Offering a silent, menacing opponent to Voyager, their malevolence seemed to signal the difficulties that lay ahead and preempted that not every enemy would be a cake-walk to overcome.
One of the issues with these guys has to be their mysterious, dangerous nature with a legend that says ships entering their territory mysteriously disappear. The attack on Voyager is well co-ordinated and quickly disrupts the ship's shields. This suggests advanced tech that could pose even more challenges in the future and although the crew barely escape, it's a threat that's cleverly left out there. Unfortunately the Borg would arrive later in the season and fill that precise same role more effectively.