Tiny spaceborne organisms that feed on the nitrium in starship components and leave a gelatinous residue behind, nearly crippling the Enterprise in Cost of Living.
Nitrium metal parasites appear in the Next Generation episode Cost of Living. In 2368 the Enterprise destroys an asteroid that threatens the planet Tessen III, and a glittering cloud of microscopic lifeforms that had been living in it slips aboard unnoticed.
The parasites digest nitrium, an alloy used throughout the ship, and turn it into a useless jelly. Replicators, transporters and other systems fail one after another, and eventually life support itself begins to shut down, leaving most of the crew unconscious.
Data, who does not need to breathe, takes the ship to the Pelloris asteroid field, which is rich in nitrium. He draws the organisms out with a beam and leaves them where food is plentiful. The crisis runs alongside Lwaxana Troi's wedding plans and her holodeck outings with young Alexander.