From Creatures Wikia
The Tribble Norns are small, fuzzy, and breed like crazy - much like their Star Trek counterparts. They are configured to possess a constantly maxed-out sex drive, grow from baby to breeding age mere moments after birth, and lay eggs extremely quickly. They change colors dramatically over the course of single generations. Putting a male and a female near each other in the same terrarium can easily result in the room being waist-deep in eggs within minutes.
Future versions may address the problem with Tribbles becoming extremely crowded easily in the large groups that naturally result from their reproductive processes.