The Enigmatic Western Spadefoot: A Closer Look at

Western Spadefoot (Spea hammondii)

It’s an unseasonably warm night for March. Five cars, all Toyotas and Subarus (and one out-of-place Mercedes Benz), linger after hours at Carnegie State Vehicular Recreation Area. This state park is set aside for off-road vehicles. It’s dry as a bone outside. The heat, coupled with the buzz and whir of wheels tearing up the landscape, makes you wonder what brought a group of biologists to seek out an amphibian.

The Western Spadefoot: A Rare Gem

“I’ve never seen a western spadefoot” is the most common statement when you bring up this so-goblin-like-it’s-cute anuran. Like many anurans, western spadefoots (Spea hammondii) are picky about where they live. There may be thousands of them in a single puddle in the middle of Bakersfield. Yet, thousands of square miles of native grassland and vernal pools are simply bereft of them.

These little creatures are also nocturnal. They are most common an hour or two after sunset. They are cryptic, often looking like and sitting still as a stone—even in the middle of the road. The keratinized protrusion on their foot, known as the “spade,” is used for digging into sand. While they may take refuge in mammal burrows, spadefoots can virtually vanish without a trace. They can scooch their butts backwards into sand and gravel within about 30 seconds.

Another feature that makes the western spadefoot elusive is misinformation. As a biologist, I have heard all my life that the only time you will see a spadefoot is during light rain. Even seasoned biologists argue that winter’s first drizzle is the only time to observe the creature. However, since 2022, BioMaAS biologists have been visiting this stretch of road. They sometimes go as late as July, observing little spadefoot metamorphs hopping across the dry road at night.

The Threats Facing the Western Spadefoot

Like many amphibians in the state, the western spadefoot is rare because it’s threatened. While only considered a species of special concern by the California Department of Fish & Wildlife, the western spadefoot is now up for listing at the federal level. Habitat loss, invasive species, and drought are all contributing factors to declines in the western spadefoot.

The point of tonight’s foray is to detect the grand villain of all amphibian threats: the fungus Batrachochytrium dendrobatidis (Bd). Bd is perhaps the primary cause for amphibian declines globally (Skerratt et al. 2007). This fungus is famously responsible for mass die-offs in Sierra Nevada Mountain yellow-legged frogs (Rana sierrae), Southern Mountain yellow-legged frogs (Rana muscosa) (Smith et al. 2016), Cascades frog (Rana cascadae) (DeLeon et al. 2017), California red-legged frogs (Adams et al. 2020), and many other species.

Researching Bd in Western Spadefoots

What is the prevalence of Bd in our friend, the western spadefoot? That’s San Francisco State Master’s Student Jakob Woodall’s research project. Under the tutelage of famed amphibian disease ecologist Vance Vredenburg, Jakob has been coming out to Carnegie. He swabs spadefoots, preserves the swabs, and sends them off to a lab to detect Bd. So far, the results have come back positive for the fungus.

Jakob plans to compare the results of these ongoing surveys to Bd detected in museum specimens. He aims to make inferences on current infection rates compared to historical ones. Additionally, he wants to see if there are differences in infection intensity between sex and age within this population.

Michael Voeltz, Lora Roame, and Shay Duffy watch researcher Jakob Woodall demonstrate how to swab a spadefoot for Bd

Jakob, a scrappy, curly-haired 28-year-old, is full of energy and information. The grim topic of his work does not dampen anyone's excitement to be in a wheelie-ravaged, disease-infected, ruderal desertscape. Interestingly, it’s not despite, but also because of the off-road vehicles that spadefoots persist here. ATVs and off-road trucks create ruts large enough for spadefoots to breed. They only need a few weeks to metamorphose (Denver et al. 1998). Meanwhile, the crushed and barren landscape allows the spadefoots to cross into appropriate upland habitat without the resistance of dense invasive plant matter.

The Process of Swabbing

Jakob is already holding up an immature spadefoot he found at the gate. The animal’s googly, catlike eyes perceive his flashlight with an unblinking look of vacant acceptance. Jakob demonstrates the proper way to hold the creature: with its front and back legs pinned between his fingers to prevent them from breaking a limb. He then places it into a container for later processing.

After a couple of hours of wandering through dry arroyos, the group has found 46 spadefoots and placed them in their own containers. The animals are brought to a table in the campground, where Jakob swabs the skin on their little round tummies, between the webbing of their toes, and their armpits. The swabs go into alcohol preservative, and the spadefoot is set free back into its habitat.

With over 60 spadefoots observed in a 3-acre parcel over the course of two hours, you wouldn’t think that they were under threat at all. “Why are there so many here if they all have Bd?” someone asks. Jakob leans his head to one side and shrugs. “One theory I have is that it’s so dry out here. The frogs spend most of their time in uplands, where it’s dry. I think that the Bd load actually subsides due to the dryness, giving the frog a fighting chance.”

Curiously, as another participant suggests, mortality in captive spadefoots cultured with Bd is higher than in the wild. This may be because husbandry experts are prone to (and even required to by permits issued by State and Federal Governments) always provide their study animals unlimited access to water. If Jakob’s theory is correct, Bd would only continue to grow within a captive setting.

The Future of the Western Spadefoot

Jakob’s study is set to continue for several more seasons. BioMaAS Biologists will be eagerly volunteering whenever he needs a hand grabbing these unique and weirdo “little buddies.” A few nights later, Biologist Shay Duffy gets the honor of releasing a big female spadefoot. We all crouch beside it as she places it on the dry arroyo pebbles.

The spadefoot spins, disoriented, using one foot to rub a bulging eye and barely remembering to close her nictitating glands. Then the chubby mother hops once, twice, and vanishes into the pebbles. Her sage-green marbled body becomes indiscernible from the stones and moss. A small, boxy male spadefoot is placed on a gravel bar. Without thinking twice, he makes a sassy wiggle of his butt and descends into the earth like Homer Simpson vanishing into a hedge.

Upon close inspection, one can barely see one golden Eye of Sauron peeking out from between the granules of dirt. A squeal of laughter and excitement erupts from the assembly—Shay, Michael, Lora, and Ivan.

“Is there anything in this world cuter than a spadefoot?” asks Michael.

References

Adams AJ, Pessier A, Cranston P, Grasso RL. Chytridiomycosis-induced mortality in a threatened anuran. PLoS One. 2020 Nov 6;15(11):e0241119. doi: 10.1371/journal.pone.0241119. PMID: 33156870; PMCID: PMC7647137.

De León, M.E., Vredenburg, V.T. & Piovia-Scott, J. Recent Emergence of a Chytrid Fungal Pathogen in California Cascades Frogs (Rana cascadae). EcoHealth 14, 155–161 (2017). https://doi.org/10.1007/s10393-016-1201-1

Denver, R.J., N. Mirhadi, M. Phillips. Adaptive Plasticity in Amphibian Metamorphosis: Response of Scaphiophus hammindii Tadpoles to Habitat Desiccation. Ecology, 79(6), 1998, pp. 1859–1872 q 1998 by the Ecological Society of America.

Skerratt LF, Berger L, Speare R, Cashins S, McDonald KR, Phillott AD, et al. Spread of chytridiomycosis has caused the rapid global decline and extinction of frogs. EcoHealth. 2007;4(2):125–34. 10.1007/s10393-007-0093-5.

Smith, TC., A. M. Picco, R. Knapp. Ranaviruses Infect Mountain Yellow-Legged Frogs (Rana muscosa and Rana sierrae) Threatened by Batrachochytrium dendrobatidis. Herpetological Conservation and Biology 12:149–159. Submitted: 3 April 2016; Accepted: 20 December 2016; Published: 30 April 2017.