American spadefoot toad
|American spadefoot toad|
|Western spadefoot toad (Spea hammondii)|
|Distribution of Scaphiopodidae (in black)|
The Scaphiopodidae are a family of American spadefoot toads, which are native to southern Canada and the United States and which extend to southern Mexico. The family is small, comprising only seven different species.
The American spadefoot toads are of typical shape to most fossorial (or burrowing) frogs, they are round, with short legs and protruding eyes. As suggested by their name, these frogs have hard, keratinous protrusions present on their feet, which help them to dig. Like most fossorial frogs, they will dig backwards into the ground, they differ from true toads because they have vertical pupils and no parotoid gland.
The American spadefoot toads are terrestrial when not underground, they are dully colored, usually a grey or dull green or brown. This is to aid in camouflage in their arid habitats.
Despite the common name and current distribution of the family, fossil evidence indicates that it once had a much larger distribution that at least reached eastern Asia; the extinct genus †Prospea is the earliest known member of this family, and is only known from Paleocene sediments in Mongolia.
Similar to other burrowing frogs, the American spadefoot toads are about 2-3 inches in length with round and stocky bodies and eyes that bulge from their heads; the name “Spadefoot” is derived from the keratinous bone in its hind legs that allow it to burrow within dirt. The skin of the toad is grey or brown in appearance and smooth to the touch.
Location and environment
Spadefoot toads are generally found in arid climates, where they spend the majority of their lives underground, generally beneath perennial ponds, creek beds, or other moisture-retaining areas. During years of sufficient rainfall, the toads surface to breed and lay eggs.
The 2 main species of spadefoot toads, they are found in different locations across North America. The Eastern spadefoot is the only species found east of the Mississippi River, ranging from New England to southern Florida; the Great Basin spadefoot and the plains spadefoot are both found in Western Canada and the northwestern U.S. but the plains spadefoot has also spread into Texas and Northern Mexico. The Couch’s spadefoot, Hurter’s spadefoot and New Mexico spadefoot are all spread across the southern and southwestern U.S. with the Couch’s and Hurter’s also reaching into Mexico. The Western spadefoot is the only species found in California, mainly southern parts of the state and extending into Mexico as well.
The toads are believed to have moved into North America from South American countries due to a changing climate, they most likely moved into the U.S. as a single species, but split up as they spread across the continent and adapted to their new surroundings. The toads prefer marsh-like environments, but only enter the water to breed, they stay buried in the soil for most of the year as a mechanism to deal with changing weather.
American spadefoot toads have a unique diet; the adults' and tadpoles' diets vary. The adults' diet consists of invertebrates, they eat flies, crickets, caterpillars, moths, spiders, centipedes, millipedes, earthworms and snails. The tadpoles' diet is related to its surroundings and food supply; when they are first born, they eat plankton. After a few days they become carnivorous and eat meat. Tadpoles sometimes resort to cannibalism to survive. After multiple experiments,Paul Székely, Marian Tudor, and Dan Cogalniceanu concluded that tadpole development is influenced by hydroperiod, or the period in which an area is full of water. Since American spadefoot toads breed in shallow waters, they are under “constant stress from drying waters, increasing temperatures, reduced food densities, and crowding”; this stress, or simply a lack of adequate food can increase the likelihood of cannabalism. If they do resort to cannibalism, their bodies can transform, they “develop larger heads, sharp beaks, stronger jaw muscles, and shortened intestine”. Researchers have concluded that this is an adaptive trait because it accelerates the rate of growth of the tadpoles by allowing for an increased calorie intake.
The eastern spadefoot entered the endangered list of Pennsylvania in 2005 (though also endangered in: Ohio, Connecticut, and Rhode Island), when living populations were only found in two of their known locations. One possibility for their lacking of population size could be that breeding pools and ponds “often dry up before the tadpoles get to complete metamorphosis”(Naish, 2015)
So far conservation efforts have made effect in the prevention of the species habitat loss. In 2012 a couple learned that thirty two acres of a property they planned to subdivide and break ground on could potentially be spadefoot habitat. So as per a species action plan put forth by Berks county conservancy and its partners, the couple would now need to seek state approval and, “hire someone familiar with the Eastern spadefoot toad to survey the tract for signs of its habitat”(Cress, 2012).
As per conservation efforts, the awareness of citizens to the endangerment of spadefoot toads in their regions has been a success. Though more effort is still needed to ensure the future of the Eastern spadefoot toad.
In 2004 the western spadefoot toad was the only member of the family Scapiopodidae to be classified as near threatened by the ICUN Red List. All other species, including the Eastern spadefoot, were listed as least concern. Presently, all species' conservation status' require reviewing.
Species of Scaphiopodidae
|Couch's spadefoot toad||Scaphiopus couchii||Couch's spadefoot toads are found in the southwestern regions of the United States and some regions of Mexico. They stay buried in the soil for 8–10 months a year and eat enough in one meal to last them a whole year. Couch's spadefoot toads' tadpoles transform into frogs in 7–8 days|
|Eastern spadefoot toad||Scaphiopus holbrookii||Eastern spadefoot toads are found all along the Eastern coast of United States. They are found from Southern New England to Florida, they are mostly found in areas with marshes and mixed hardwood swamps. They can grow up to 3 inches long.|
|Great Basin spadefoot toad||Spea intermontanus||The Great Basin spadefoot toad is found in the area spanning from south-central British Columbia, Canada to north Western states of the United States of America such as Wyoming, Oregon and even California. Most of the Great BasinsSpadefoottoadss are nocturnal and their diet includes of invertebrates such as ants.|
|Hurter's spadefoot toad||Scaphiopus hurterii||Hurter's spadefoot toads are found in the southern states of the United States of America, such as Texas, Arkansas, Oklahoma and Louisiana. These toads were once thought to be a subspecies of the Eastern spadefoot toad.|
|New Mexico spadefoot toad||Spea multiplicata||The New Mexico spadefoot toad is found in Mexico and the U.S. states of Arizona, New Mexico, Nevada, Utah and Colorado. It grows up to 2.5 inches in length|
|Plains spadefoot toad||Spea bombifrons||The plains spadefoot toad is found in southern Alberta, Canada, central states of the United States and northern parts of Mexico. They can grow up to 2 inches in length, they can be found in the areas with sand or gravel in soils near temporary bodies of water.|
|Western spadefoot toad||Spea hammondii||The western spadefoot toad can be found only in California and Baja California, Mexico. Unlike other toads, the western spadefoot only enters the water to breed.|
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