An axolotl (ax-a-lot-l) is a creature with big frilly gills like a lion’s mane, tiny eyes with no eyelids and a mouth in the shape of a smile. They come in lots of colors: pink, black, golden or gray.

You may have seen axolotls—an amphibian in the salamander family with a permanent smile and pink, feathery gills—in a pet store or as a plushie in a window, but the endearing animal's popularity seems ...