AT A GLANCE
- Common Name: Plains Spadefoot Toad
- Scientific Name: Spea bombifrons
- Category: Amphibians
- Subcategory: Frogs & Toads
- Range: Central North America, throughout the Great Plains from southern Alberta and Saskatchewan, Canada, south through the United States (Montana to Texas) to northern Mexico (Chihuahua and Tamaulipas)
- Habitat Type: Shortgrass and mixed-grass prairies, semi-arid plains, sagebrush shrublands, floodplains, and agricultural fields with loose, sandy, or gravelly soils
- IUCN Red List Status: Least Concern
- Lifespan: 8 to 12 years
- Diet: Carnivorous/Insectivorous (nocturnal hunting for crickets, beetles, grasshoppers, moths, ants, spiders, and earthworms)
- Average Size/Weight: Snout-vent length 3.8 to 6.5 cm; weight 12 to 25 g
- Key Defining Feature: Plump, round-bodied burrowing toad with vertical cat-like pupils, a distinctive bony boss (bump) between its eyes, and a single, sharp, black sickle-shaped digging spade on each hind foot
Overview
The Plains Spadefoot Toad (Spea bombifrons) is an extraordinary, subterranean amphibian native to the vast, windswept grasslands and semi-arid prairies of the North American Great Plains. Belonging to the family Scaphiopodidae, this plump, secretive survivor spends upwards of ten to eleven months of the year completely buried deep underground in self-excavated burrows. It emerges only after violent, torrential summer thunderstorms to engage in one of the most explosive, rapid breeding cycles known in the entire animal kingdom.
Biology and Physical Characteristics
Spea bombifrons has a short, stout, globular body with smooth, moist, glandular skin colored greyish-green, sandy-brown, or yellowish-tan, dotted with subtle dark olive blotches and tiny reddish tubercles. Its head is blunt, characterized by large, bulging golden eyes with vertical, cat-like slit pupils. Crucially, it features a prominent, hard, bony prominence or ‘boss’ on the skull between the eyes, which distinguishes it from related spadefoots. Its hind feet are equipped with a single, enlarged, sickle-shaped, pitch-black keratinized spade (metatarsal tubercle) used as a biological shovel to dig backwards into loose sandy soil.
Behavior and Ecology
When the summer sun bakes the prairie soil, the Plains Spadefoot digs backwards into the earth, rotating its hind legs to vanish beneath the surface within minutes. It burrows up to a meter deep into damp soil layers, where it produces a hardened, semi-permeable cocoon of shed skin cells to prevent dehydration during months of drought. When heavy, drenching rainstorms generate low-frequency acoustic vibrations that penetrate the soil, thousands of spadefoots dig their way to the surface simultaneously. Congregating in temporary prairie potholes and flooded roadside ditches, males produce loud, duck-like snoring bleats. Their tadpoles exhibit remarkable phenotypic plasticity, with some developing into carnivorous, large-headed morphs that feed on fairy shrimp and other tadpoles to metamorphose in as little as 12 to 14 days before the temporary pool evaporates.
Conservation and Human Impact
The Plains Spadefoot Toad is assessed as Least Concern on the IUCN Red List due to its immense geographical range across the North American continent. While overall populations are secure, localized declines have occurred in agricultural areas where deep tilling crushes underground burrows and wetland drainage eliminates temporary breeding playas.
Interesting Factoid
The Plains Spadefoot Toad can remain buried underground for nearly an entire year without eating, and when monsoon rains fill temporary puddles, its tadpoles can hatch, grow, and transform into fully formed toads in just twelve days before the water dries up.