Wookie Balls

Star Trek has a rich supply of aliens. Many though are just an actor with a little latex or a stupid haircut. Not theses guys though...

Tribbles are little asexual balls of fur that breed like crazy. In fact they are born pregnant. Whenever they show up in the show they end up multiplying out of control consuming resources at a dangerous rate. Otherwise they are completely harmless and kind of cute, even Spock thought they had a calming purr.

And if you are insane you can buy an actual tribble that was used in the series.