Let’s talk for a minute about the plains spadefoot and their awesome vertical-pupilled eyes. You might think the spadefoot is a toad. If so, you’re wrong …kind of. Also, you might think the word “pupilled” isn’t a real word, and anyway it should only have one ‘L’. Wrong again – (I just looked it up).
Toads, you see, have dry skin with little “warts” (no,they aren’t really warts, and don’t cause you to get warts). Spadefoots have the kind of moist, slightly slimy skin that is more typical of frogs. In addition, the plains spadefoot is missing the raised parotoid glands behind its eyes that are typical of true toads (see photo below). So, clearly, the spadefoot is not a toad, it’s a frog.
Well, wait just a second, Herp-a-long Cassidy. It’s not that simple. As it happens, Anurans – the taxonomic group that includes frogs and toads – is a kind of spectrum, rather than two distinct types. There are “true frogs” and “true toads”, but there are a lot of in-between species too, which don’t really fit either category. Spadefoots don’t really identify as either frogs or toads.
Regardless of labels, the plains spadefoot is a fascinating creature, and one that is rarely seen, even in states like Nebraska where it is considered to be common. In fact, despite the fact that it’s a grassland animal, and I’ve been exploring and studying grasslands for about 25 years, I’d never seen one in person until last summer. (Thanks to Keith Geluso, by the way, for finding one at The Niobrara Valley Preserve and allowing me to photograph it!).
The reason they’re rarely seen is that plains spadefoots spend the vast majority of their lives underground, emerging only during and after heavy rains between April and July. They are known as “explosive breeders” because they have to breed and get their offspring to maturity very quickly. It’s a race between tadpoles and the temporary rain-filled ponds. To help ensure survival, there are two types of spadefoot tadpoles; herbivores and carnivores/cannibals. If the tadpole’s pond comes and goes so quickly that no algae or other vegetation has time to grow, at least some tadpoles can still find food – even if that food consists of siblings. Spadefoots can go from egg to mature in around two weeks if they have to, which is pretty impressive.
Except for the brief periods when plains spadefoots make an appearance to breed and feed, they basically live their lives underground, in a kind of dormant state. Their “‘spadefoot” moniker comes from a dark hard “spade” on their rear feet, which they use to quickly burrow down into loose soil. While it might seem crazy that spadefoots live almost all of their lives in dormancy, there are a couple nice perks associated with the strategy. First, it’s a pretty slick way to avoid predators. Second, it allows spadefoots to colonize areas of grasslands far from permanent water – they don’t need access to streams, ponds, or lakes like their other Anuran cousins. Instead, they just sit in quiet solitude until a good hard rain, and then party down. All things considered, that might not be a terrible life.
Many thanks to Dan Fogell, both for his excellent book, “A Field Guide to Amphibians and Reptiles of Nebraska”, and for helping me better understand the frog-toad-etc spectrum this week.