Plains spadefoot

Until 2014, every field guide to Yellowstone would have told you the plains spadefoot wasn’t there. Then researchers ran genetic tests on a breeding pond near Fountain Flat Drive and found the toad had been living in the park the whole time, unnoticed, because a plains spadefoot spends almost its entire life underground. It surfaces only on the handful of nights a year when rain fills a pool deep enough to breed in, digging its way back down afterward with the hard black spade on each hind foot, backward into the soil, sometimes three feet deep.

That buried life makes the pond it breeds in more valuable, and more dangerous, than it looks. Eggs laid in a pool that might not last the month have to become toadlets fast, and plains spadefoot tadpoles have a trick for speeding that up: in a crowded, drying pond, some of them switch into a bigger-mouthed “cannibal” form and start eating their pond-mates instead of algae. The extra protein lets the cannibal morphs finish developing sooner than the ones still grazing, a shortcut that only pays off because the alternative is drying up with legs half grown.

Most years, the whole event happens and ends within days, and the toads go back to being invisible again — buried under the sand at Great Sand Dunes, under the prairie at Badlands, under ground nobody has genetically tested yet. The next storm is the only thing that will bring them back up.