Small furry creatures that breed fast.
Tribbles are small, round, furry creatures that purr and have a soothing effect on most humanoids. They are born pregnant and reproduce at an astonishing rate whenever they have plenty to eat, so a single tribble can turn into thousands in a matter of days.
In the original series episode The Trouble with Tribbles, the trader Cyrano Jones sells tribbles on Deep Space Station K-7, and one given to Uhura soon leads to an infestation aboard the Enterprise. The tribbles get into the station's store of grain intended for Sherman's Planet, revealing that it had been poisoned. They also screech at Klingons, which exposes the Federation official Arne Darvin as a disguised Klingon agent.
Tribbles returned in the animated series episode More Tribbles, More Troubles and in Deep Space Nine's Trials and Tribble-ations, where Worf explains that the Klingons later wiped them out on their homeworld. They have also appeared in Enterprise, Star Trek Into Darkness, the Short Treks episode The Trouble with Edward and Lower Decks.