They have different markings on their bellys. Though I have to pick em up and look at the tumms to tell that way. Mostly you can go by personality. They have 4 sisters as well that look like smaller versions of them. Personalities are very very different however on each one. If it jumps on you continuously and then rolls over like a spaz when you chase it-that would be Fizzly. if it's huge and like glue to the humans and squeeks anytime anyone jumps at him that would be Moojoo. If they are play fighting non stop, have no fear of anything and act like they own the house and are inseparable-that would be Zumbug and Buzzle...anyways you get the idea.They're all adorable but like wow how do you tell them apart??