The Secret Life of American Spadefoot Toads: A Complete Guide

The American spadefoot toad, from the fascinating amphibian family Scaphiopodidae, is one of the most elusive and mysterious frogs native to North America. Unlike their close relatives, the true toads (Bufonidae), American spadefoot toads have a smoother skin texture and lack parotoid glands behind their eyes. But what makes them truly unique are the sharp, horny spade-like projections on their hind feet that enable rapid underground burrowing.

This species leads an incredibly secretive life, hiding beneath the soil for most of the year and emerging only during heavy rains to mate and lay eggs. This comprehensive guide dives into the obscure world of these remarkable burrowing frogs. It highlights why they are one of the most distinctive amphibians on the continent.

With over 90 known species, America has a rich diversity of fascinating frogs and toads. While most have adapted to aquatic habitats, some have evolved to survive in the harshest and driest environments. Among these are the spadefoot toads belonging to the family Scaphiopodidae. Two recognized spadefoot toad genera in North America are Spea and Scaphiopus.

Initially, American spadefoots were grouped under the Eurasian spadefoots in the Old World genus Pelobates until taxonomists identified enough unique traits to place them in their own distinct family. Today, around 7 species of these burrowing frogs are found across North America.

The spadefoot toads inhabit areas with dry, sandy, and loose soils across southern Canada, throughout the United States, and into northern Mexico. These arid habitats include shortgrass prairies, desert grasslands, scrublands, and barren plains. Spadefoots are remarkably well adapted for a terrestrial and largely subterranean existence in these challenging environments where most frogs would perish.

Their plump, rotund bodies have relatively small limbs, and their eyes are perched high on the head, giving them a unique toad-like appearance. The eyes have vertical slit-like pupils similar to many reptiles and catfish. Their dull and drab coloration of olive, grey, tan, and brown hues provides excellent camouflage when burrowed underground or on the surface.

But the most distinctive feature of American spadefoot toads is the sharply pointed, black, hardened projections on their hind feet from which their name is derived. These keratinous structures are not actual “spades” but rather horny protrusions of bones in the feet. Nevertheless, they serve an indispensable purpose – digging.

American spadefoot toads can rapidly burrow backward into the sandy ground when threatened using their powerful hind legs and these spade-like feet. Some species have even been documented digging as deep as 1.3 meters underground. The spades on the feet and countersunk lower jaws also aid movement through loose substrates.

Fossorial Lifestyle

Burrowing or living underground is known as a fossorial lifestyle. American spadefoot toads are profoundly fossorial, spending up to 99% of their lives inside caves 1 to 3 feet beneath the surface. Here, they avoid desiccation in the extreme heat and arid conditions. Their burrows are typically constructed in loose, sandy, or fine gravelly soils.

Spadefoot toads occasionally emerge from their underground haunts during wet weather, such as heavy rains, when their temporary breeding ponds form. They also may emerge at night to feed when surface temperatures are more relaxed. However, most of their lives are confined to their gravelly burrows.

To survive the dry conditions underground, spadefoot toads have unique adaptations to prevent water loss. Their skin contains specialized mucous glands, which secrete a viscous, jelly-like substance. This helps maintain skin moisture and water balance while burrowed. Spadefoots can absorb water directly through their ventral skin surface if the soil moisture drops too low.

Their permeable skin can quickly uptake water, sometimes doubling their weight in just a few minutes after a desert rain shower. Spadefoots also have the remarkable ability to achieve a hibernation-like state underground, known as estivation. Here, they can slow their metabolism immensely to conserve energy and fat reserves when food is scarce. Their biology is finely tuned to persisting in challenging underground conditions.

Explosive Breeding

Spadefoot toads may spend nearly their entire lives hidden below ground. Still, they emerge in sizeable explosive breeding congregations when weather conditions are right. These unique amphibians are adapted to take advantage of short windows of rainfall to mate and lay eggs in temporary ponds and rain puddles.

They spend long periods underground waiting for the perfect storm – intense rain followed by warm, wet nights. Spadefoots will erupt to the surface in droves when these conditions finally occur after months or years of waiting.

Hundreds of male spadefoot toads converge on newly formed ponds and puddles to breed. Their mating calls create a loud chorus, attracting females to lay eggs in the temporary waters. Different species exhibit unique calls, some sounding like bleating sheep, a crying baby, or duck quacks. This frantic activity lasts just a few nights before the adult spadefoots retreat into their burrows. Their life cycle is so rapid that tadpoles hatch within a day or two of the eggs being laid.

Some species, such as Couch’s spadefoot toad, have adapted to metamorphose from eggs into tiny spadefoot toadlets in an incredible 7-10 days to use fleeting desert rain pools. Specific morphological adaptations facilitate their rapid development. The tadpoles exhibit bulging guts, reduced mouthparts, and specialized dentition to allow for quicker digestion.

They also utilize fat bodies for energy rather than obtaining food. Such incredible transformations allow spadefoots to succeed in temporary aquatic habitats that quickly evaporate or become too hot in arid regions.

Cannibalistic Tadpoles

The frenzied mating free-for-all and abundance of eggs laid by spadefoot toads result in highly dense tadpole populations competing in confined rain pools and puddles. This has led to the evolution of cannibalistic behavior in some species. When food is scarce, the tadpoles start feeding on each other!

Interestingly, spadefoot tadpoles exist in three different morphs. Most tadpoles are smaller omnivore morphs, feeding on detritus and dead organic matter. Some develop into more giant carnivore morphs with serrated mouthparts and longer guts specializing in eating fairy shrimp and other tadpoles. The third morph is cannibalistic-morphs, which solely hunt and consume other tadpoles. Their morphology maximizes energy intake from meat to fuel their rapid development.

The ratio of morphs in tadpole populations depends on habitat conditions like food availability, predation risk, and competition. More limited resources drive increased cannibalistic and predatory behavior. Evidence suggests that the tadpoles can recognize and avoid eating close relatives, instead selectively feeding on unrelated individuals! This likely evolved to promote their genes.

The brief period as tadpoles is a challenging survival game driven by the pressures of limited resources and rapid development against time before the pool dries up. It’s a battleground where only the fittest morphs will successfully metamorphose.

Species Spotlights

America has a remarkable diversity of spadefoot toad species with unique traits and habitat affinities. Here are some of the most fascinating:

Eastern Spadefoot

The Eastern Spadefoot Toad (Scaphiopus holbrookii) is among the most widespread American spadefoot species. Their range spans from the sandy coastal plains along the Atlantic to the Mississippi River and parts of the Appalachians. These stocky toads reach lengths of 1.5-2.5 inches. Their brown or grey skin contains faint striping, and they often have striking lemon-yellow eyes with elliptical pupils. This species is expected in the southeastern states but endangered in the northern extremes of its range.

Eastern Spadefoots prefer sandy habitats with open, sunny areas like pine woods, meadows, and scrublands. They spend nearly their whole lives underground in burrows up to 3 feet deep, sealed with gel. Their explosive breeding happens in ephemeral woodland ponds and floodplain pools. The tadpoles can transform in as little as 12-21 days before the waters dry. Their calls sound like a bleating sheep!

Great Basin Spadefoot

The Great Basin Spadefoot (Spea intermontana) occupies some of the harshest deserts in the American Southwest. Their range spans the Mojave and Sonoran deserts between 400-2700 m elevation. These pale grey or tan toads reach lengths of 1.5-3 inches. Their pupils are vertical, and they lack contrasting stripes.

As their name suggests, Great Basin Spadefoots primarily occur in the Great Basin and surrounding arid habitats. They are well-adapted to dry conditions and can remain underground for years, waiting for perfect post-rain breeding conditions. Their explosive breeding happens in temporary desert rain pools. Tadpoles transform in 14-50 days. These toads are highly nocturnal and secretive. Their calls sound like a bleating lamb or crying baby. The Great Basin Spadefoot is threatened by habitat loss and modification. Conservation efforts aim to protect suitable breeding sites and terrestrial habitats for this desert-adapted species.

Couch’s Spadefoot

The diminutive Couch’s Spadefoot Toad (Scaphiopus couchii) measures 1-2 inches long. Their stocky body is tan, olive, or gray with darker blotches. This small desert species inhabits arid grasslands and scrublands of the southern U.S. prairies and plains below 1500m. Nine separate subspecies occur across different regions.

Couch’s Spadefoot is the fastest-developing amphibian in North America. After mating in warm post-rain pools, their eggs can hatch into tadpoles in 16-24 hours! The tiny tadpoles undergo incredible metamorphosis into toadlets in as little as 7-10 days. This extremely rapid pace of development allows them to transform before their ephemeral breeding sites dry up.

This species spends much of its time in burrows up to 90 cm deep. Their explosive breeding calls sound like the bleating of sheep. Significant threats to Couch’s Spadefoot include habitat destruction, grazing, agriculture, and groundwater pumping. Several subspecies have strictly limited distributions and face endangerment.

Plains Spadefoot

As their name suggests, the Plains Spadefoot (Spea bombifrons) primarily inhabits shortgrass prairies and dry grasslands of the Great Plains in the USA and Canada. They range from South Dakota down through Texas and New Mexico. These plump toads reach 1.5-3 inches long. They are light gray or tan with darker mottling and have striking orange-red coloration on the belly and iris.

The Plains Spadefoot epitomizes adaptations for an arid, prairie existence. Almost all their lives are spent underground in deep burrows with side chambers used for estivation during droughts. They emerge after heavy summer rains to breed explosively in temporary rain pools. Tadpoles transform in 11-19 days. This is one of the few American spadefoots currently secure from significant threats due to large intact prairie habitats. Their call sounds like the bleat of a sheep.

Western Spadefoot

The Western Spadefoot (Spea hammondii) occupies arid regions of the western United States and Mexico. Their range spans southeast California, southern Nevada, southwestern Utah, most of Arizona, and western New Mexico down into Mexico. As their name suggests, these are Western relatives of the Eastern Spadefoot. Adults reach 1.5-3 inches long and are gray or tan with darker spots and stripes.

This species occupies desert ecosystems like grasslands, scrublands, and alluvial fans. Their fossorial nature leads them to spend most of their time in underground burrows up to 1 meter deep. Explosive breeding occurs in temporary rain pools and puddles. The tadpoles transform in 14-60 days. Threats include habitat loss from agriculture, urbanization, and livestock grazing. Some isolated populations now face destruction.

Threats and Conservation

Most American spadefoot toad species face significant threats primarily driven by habitat destruction. Creating suitable burrowing sites, maintaining underground refuges, and conserving ephemeral breeding sites are critical for protecting these fossorial amphibians. Unfortunately, human activities have heavily impacted and modified many of the ecosystems spadefoots occupy.

Urbanization and agriculture have destroyed or fragmented most natural habitats once found across the prairies, plains, and deserts inhabited by spadefoot toads. Sandy scrubland and desert ecosystems have been lost to crop cultivation, development, and grazing. This has eliminated terrestrial habitat and burrowing sites needed by spadefoots.

Land conversion has also disrupted hydrological systems and destroyed the temporary wetlands required for breeding. Groundwater pumping, livestock use, and eutrophication frequently eliminate the freshwater pools these toads need for explosive mating congregations.

Climate change presents an additional threat by altering rainfall patterns and shrinking suitable habitats. Already living on the edge of their physiological limits, spadefoots are highly vulnerable if arid conditions become more severe. Some species have documented slow development, decreased survival, and failed recruitment during droughts. Any disruption to the precise conditions spadefoot toads need to persist and breed can significantly impact these precarious environments.

While some species, like the Plains Spadefoot, remain secure in large intact prairies, others now face endangerment across parts of their range. New Mexico, Arizona, and Mexico contain several spadefoot species with isolated, declining populations vulnerable to extinction. However, conservationists are taking steps to protect critical habitats and breeding sites. Partnerships between governments, landowners, researchers, and NGOs have helped survey and conserve spadefoot populations. Public education programs aim to generate awareness and support for conserving these remarkable yet obscure desert amphibians.

One conservation success story involves the Eastern Spadefoot, listed as endangered in Pennsylvania, where it reaches the northern extremities of its range. By studying their habitat requirements and movements, researchers aided state officials in developing a species action plan. Protected areas were established around breeding ponds on public lands.

Agencies also maintained nearby roadside ditches and woodland pools to provide additional breeding habitat. Thanks to these initiatives, most historical Eastern Spadefoot populations in Pennsylvania remain intact. This demonstrates that targeted conservation action informed by research can safeguard vulnerable peripheral populations. Maintaining strongholds while improving connectivity will offer the best future for threatened spadefoot species across North America.

Observing Spadefoot Toads

The secretive habits of American spadefoot toads make them challenging to observe in the wild. Their burrowing lifestyle means they spend little time above ground except during explosive breeding events. However, witnessing these remarkable amphibians in their natural habitat can be an enriching experience for patient observers. Here are some tips:

  • Time it right – Target nights or days immediately after heavy monsoon rains from July to September when spadefoots emerge to mate and lay eggs.
  • Follow the noise – Listen for choruses of bleating or duck-like breeding calls near temporary wetlands.
  • Focus your search – Survey along muddy edges and shallows of rain pools, puddles, and ditches where males congregate.
  • Look down – Scan for toads around the water’s edge and use flashlights to detect their eyes shine.
  • Consider the burrow – Gently excavate around potential tunnel openings in loose soil where you suspect spadefoots may be hiding.
  • Respect their habitat – Follow ethical guidelines, avoid disturbing breeding sites, and correctly fill in any burrows dug.
  • Share your observations – Consider recording sightings through citizen science platforms like Natural Atlas to contribute data to research and conservation.

Get Involved in Citizen Science

Citizen science refers to public involvement in research efforts by collecting or analyzing scientific data. Citizen observations provide critical information to researchers when it comes to elusive and obscure species like the American spadefoot toad. Recording sightings help generate valuable data on where specific species occur, their geographic distributions, population trends, and habitat use. These public contributions build our knowledge of poorly understood organisms and aid conservation efforts.

Natural Atlas is one platform where citizen scientists can log and map their spadefoot toad observations, photos, audio recordings, and field notes. The data is made freely available so researchers can analyze habitat associations, and range boundaries, and identify new populations. Contributors can also connect and discuss their findings in the community forums. Your observations could assist scientists in making discoveries!

When photographing or handling spadefoot toads, follow ethical practices that ensure their welfare and minimize disturbance. Avoid using flash, keep handling brief, and do not disturb sensitive breeding sites. If you encounter injured individuals, document it but leave the rescue to permitted wildlife rehabilitators. Following these guidelines allows us to study spadefoot toads while protecting populations and respecting these marvelous yet sensitive creatures.

Conclusion

The obscure world of the American spadefoot toad, hidden below the soils of deserts and prairies, is a whole of incredible adaptations like rapid metamorphosis, kin-recognizing cannibalistic tadpoles, and horns adapted into shovels. This ancient family of burrowing frogs has evolved to take advantage of the harshest environments across North America. Hopefully, this guide provided some fascinating insights into the secret life cycle of spadefoots while highlighting the need to protect the ephemeral wetlands and loose sandy soils these species rely on.

Though elusive, the spadefoots play essential roles in food chains, nutrient cycling, and ecosystems. With expanded conservation efforts, citizen science monitoring, and habitat management, we can ensure future generations have the opportunity to marvel at the remarkable world of American spadefoot toads.