Tribbles

Tribbles (Polygeminus grex) are small, non-sapient lifeforms originating from Iota Geminorum IV. Known for their prodigious reproductive rate, these round, furry creatures emitted cooing sounds while touched, which had a tranquilizing effect on the Human nervous system.

Biology
On their own, tribbles are quite incapable of directly harming sentient beings - they do not even possess 'teeth' as such and are also fairly slow. Nonetheless, if their population growth is left unchecked they can rapidly multiply and devastate entire ecosystems on a planetary scale.

Fully half of a tribble's entire metabolism is devoted to reproduction. Born pregnant, a single tribble with sufficient food can quickly increase its number exponentially through asexual reproduction, bearing an average litter of ten every twelve hours. Tribbles are hermaphroditic, possessing both male and female reproductive organs, which makes them capable of self-fertilizing at will. Given sufficient food supply, a single tribble can give rise to progeny numbering over one million in less than four days.

On their homeworld, tribble populations are kept in check by a large number of reptilian predators.