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Plains Spadefoot

The Plains Spadefoot (Spea bombifrons) is a nocturnal toad that spends most of its life underground. The spadefoot toads are not true toads (Family Bufonidae) but belong to the primitive family Pelobatidae. The Plains Spadefoot is considered a Blue List species in Alberta.

Spadefoot toad species are confined to the more arid regions of western North America. The Plains Spadefoot occupies habitats ranging from deserts in the southwest United States to aspen parkland in the Canadian prairies. In Alberta, the Plains Spadefoot primarily occurs in the Grassland Natural Region although there have been observations from the Parkland Natural Region.

Spadefoot toads resemble true toads (Family Bufonidae) in body form but have smoother, thinner skin like that of frogs. Unlike true toads, spadefoot toads have a vertical elliptical pupil and no parotoid gland. The spadefoots are named for their large, sharp metatarsal tubercles that are used to dig backwards to depths of almost 1m. The Plains Spadefoot is active in Alberta from late May to fall, but it is seldom seen outside of breeding periods.

During periods of drought, Plains Spadefoots do not remain underground for years at a time but, especially during humid weather, emerge to forage during evenings. As summer progresses and the soil becomes drier, Plains Spadefoots burrow deeper into the soil and emerge less frequently. During very dry conditions, Plains Spadefoots may burrow 60 to 90 centimetres below the surface. Plains Spadefoots will most often burrow along the edge of a solid object or near a plant that offers security or shade.

Plains Spadefoots burrow deeply to avoid freezing and desiccation during the winter. In Arizona, Plains Spadefoots have been found at depths of 91 cm during hibernation. There are no published accounts of hibernation depths in Canada. The Plains Spadefoot is intolerant of freezing and must burrow below the frost line during the winter. However, this species does exhibit super cooling to -4.3 degrees Celsius (toads did not freeze at temperatures as low as -4.3 degrees Celsius), which would help the Plains Spadefoot avoid freezing in shallower burrows during the winter.

Spadefoots forage above ground and prey on a variety of insects. Insect prey includes flies, moths, beetles and various spiders.

Plains Spadefoot

Plains Spadefoot