While digging ditches for water lines I ran into some neighbors I never knew I had who were living beneath my feet.
Several feet down in the soil the backhoe uncovered what I thought was a toad or frog. The climate of Cedar Fort Utah, the area where we were digging, is quite hot and dry and the ground is extremely hard and rocky, but when I held the amphibian in my hands it was cold and determined to jump away from bondage. I set it down in a cool, safe place where it soon began digging backwards into the ground. I watched it until it had dug down out-of-sight. It was quite surprising to me that an amphibian was making its living so far underground and in such an arid place. After looking through an identification book on Amphibians I am pretty certain that I had met a Great Basin Spadefoot Toad.
The Great Basin Spadefoot Toad (Spea intermontana) is an amphibian who has evolved many ways to survive in the cold deserts of Utah. They live in various habitats from sagebrush flats and juniper-pinion forests, to pine and deciduous forests. They can be found in British Columbia, Washington, Oregon, Utah, Nevada, Idaho, Colorado and Wyoming and are quite common throughout their range.
Great Basin Spadefoots have several adaptations that make them particularly successful in arid climes. Firstly, burrowing. The name, Spadefoot, refers to the spade-shaped, keratinized growth on their back feet that they use to burrow backwards into the dirt. Burrowing is how they survive hot and dry times; it is also how they avoid predators. Normally they either use an abandoned mammal burrow or dig their own to a depth of about 2-3 feet though they've been found as deep as 15 feet down in the ground! Down there it is cooler and often moister. It is amazing to me that they can breathe buried so deep in the dirt. Amphibians' respiratory system is unique, however, for it allows them to breathe with lung equivalents like we do, but they can also breathe through their skin. Somehow they survive.
What are they doing while below the surface? From about October to April they're hibernating and during particularly dry summer months or hot spells they are aestivating. Aestivation is like hibernating in that they lower their metabolic rate and body temperature to conserve energy in a sleep-like state, but the Great Basin Spadefoot will also build itself a mucus cocoon to prevent water loss as it waits for the drought to end. Additionally, during aestivation, the Spadefoot stores its urine and as the urea concentration builds up inside its body it causes any residual moisture in the soil to be absorbed through its skin by osmosis.
Another adaptation used by the Great Basin Spadefoot Toad to survive the desert is explosive breeding and a short development period. Normally, they won't breed during dry seasons unless they are by a stream, pond or some kind of human-made water reservoir like a cattle trough or a pond. When there is no constant water source the Spadefoots are waiting below the surface for a heavy rain. After a good rain they come to the surface and the males start singing................
...........until a female, enticed by the song, approaches and they mate. Eggs have to be laid and fertilized in water. I've seen conflicting sources, but the timeframe for development from tadpole to adult is about 3-6 weeks. Tadpoles have to grow fast because water sources in the desert are often transitory and dry up quickly (hopefully not too quickly for the tadpoles to mature into adults when they are old enough to dig burrows and survive the drought).
Another Spadefoot Toad innovation for living in deserts is a nocturnal activity pattern. On nights where it is slightly humid, like after a rain, they come up to ground level and hunt for insects; generally, they eat ants, beetles and grasshoppers though other insects can be on the menu if present. Because they are active on the surface at night they have to worry about nighttime predators like owls, foxes, snakes, skunks and the like. Spadefoot Toads have a slightly irritating skin secretion, that can cause an allergic reaction in some humans and can cause a burning sensation if it gets in eyes or noses, that seems to somewhat deter predation.
No one is certain how long Great Basin Spadefoot Toads live, but bone analysis has found individuals as old as 13 years which is quite amazing to me considering that they are amphibians living in a desert.
The Great Basin Spadefoot made me aware of how few neighbors I'm aware of. There aren't just humans living in my neighborhood afterall. Just under my feet was a creature I'd never known was there even though I'd lived in the area for 20 years! It makes me wonder what other life-forms might be living near and far that humans in general are not aware of. When I'd read just a little bit about Spadefoot Toads it struck me just how beautifully adapted to their environment organisms can evolve to be, even producing seeming paradoxes like amphibians thriving in a bone dry desert.