Their molecular structure naturally stores enormous quantities of nucleogenic energy, and they are known to emit large quantities of antimatter. They are only able to survive for a few seconds in our realm. Physically, the creatures resemble flying sirens, with an elongated body with four-fingered humanoid arms and no legs. They are mostly dark green, with a yellow ventral surface; and have noseless faces with a pair of black eyes and a toothed mouth.
Although not usually hostile, they have the ability to kill humanoids almost instantly by dehydrating every cell in their bodies.
The USS Equinox learned of the existence of these creatures after being stranded in the Delta Quadrant. Short on supplies and moral the Starfleet personnel were helped by the Ankari who before blessing the crew's journey home. Upon witnessing the creatures emerge, the Equinox crew discovered that the Shrieks were emitting high levels of antimatter. Interested in this the crew subsequently constructed a multiphasic chamber to confine the lifeforms for the purpose of study. However they inadvertently killed the creature, but from the corpse they learned that the nucleogenic energy stored within could be used to enhance their warp core to speed their journey home. Using this augment their warp engine they could ttravel over ten thousand light years in less than two weeks. However, the energy extracted from a single lifeform could only increase their warp factor by 0.03% for a single month, thus the crew began to systematically lure and murder more of the lifeforms. These actions did not go unnoticed by the Shrieks or the Ankari, the former began to attack Equinox repeatedly until the arrival of the USS Voyager. While the crew of the Equinox kept their sister ship i the dark of their questionable actions, it was later revealed when the Equinox chose to attempt to destroy Voyager and kidnap two of their crew mates. Learning the full story of what they did, Captain Janeway angered at this betrayal to the ideals of Starfleet relentlessly pursued the rogue ship. Reaching out to the Ankari to act as intermediaries to speak with their alien benefactors Janeway promised the Shrieks that they would be allowed to destroy the Equinox to end these crimes, but until she captured the crew of the Equinox to stand trial for their actions.
A species called Ankari has created technology that allows them to summon the lifeforms into our normal realm for a few seconds. They use this on spiritual practices as they regard the nuclegonic lifeforms as spirits of good fortune. The term "nucleogenic" strongly implies that the lifeforms run on a nuclear rather than chemical metabolism, and might explain why their bodies can generate so much power, enough to propel a starship more than 10,000 light years in less than two weeks.
- Star Trek Voyager: Season 5: Episode 26: Equinox
- Star Trek Voyager: Season 5: Episode 27: Equinox II
- The aliens in the show were unnamed, though in an unofficial Delta Quadrant Guide, they are named as Shrieks.