Plains Spadefoot
Last Review/Updated: May 30, 2002
Scaphiopus bombifrons
Description
The plains spadefoot is a plump toad with short limbs and a pronounced bump, underlain with bone, between the eyes. A full-grown adult can attain a total length of 35-60 mm. The colour varies from brown to dull green, usually with four lighter stripes on its back. The small warts on its back are tipped with yellow or orange. Spadefoots get their name from the "spade"—a wedge-shaped projection (tubercle) on the inner surface of the hind feet used for digging their burrows. These toads resemble both frogs and toads. Their skin is relatively smooth and moist like a frog, but they have some warts on their backs and live on land like a toad. Spadefoots can be distinguished from the true toads of Alberta by 1) their relatively smooth skin; 2) the pupil of the eye is vertical, and 3) the lack of an enlarged parotoid (poison) gland on the shoulders.
Natural History
While the spadefoots are active from spring until fall, they are rarely seen outside of the breeding period. They inhabit arid and semi-arid regions and survive there by using their "spades" to tunnel backwards and downwards in a corkscrewlike motion into the soil until they find moisture. They have been found as deep as one metre below the surface. Spadefoots are nocturnal, and are especially active after a rainfall. They eat a variety of invertebrates such as ants and beetles. When handled, they emit a sticky secretion. The plains spadefoot is currently on the Blue List in the Status of Alberta Wildlife because it is considered to be at risk, or vulnerable.
The plains spadefoot is the subject of some controversy, taxonomically speaking. While most guides to amphibians place it in the genus Scaphiopus, a few references state that it is a member of Spea.
Breeding
Breeding generally occurs in May (but as late as July) in temporary ponds when spadefoots emerge after heavy rains. Males arrive at the ponds and begin calling to attract females. Their call is short and sounds somewhat like a duck. Once breeding occurs, the eggs are laid in clusters of 10-250 attached to vegetation, a few centimeters below the surface of the water. Within two days, the eggs have hatched. If there is insufficient rain, the spadefoots may not breed at all that year.
Larvae
Because spadefoots are adapted to temporary water bodies, the developmental process is quite rapid and 21-40 days after hatching the tadpoles will have transformed into toads. The tadpoles are a light grey or brown on top and lighter underneath. They can reach a length of up to 68 mm.
DistributionWithin Alberta, the plains spadefoot is limited to the south of the province, primarily in short-grass prairie. Known locations tend to be in natural habitats in areas of sandy soil. MonitoringPlains spadefoots are primarily nocturnal, making them difficult to locate outside of the breeding season. Once the spring rains begin, breeding will follow quickly. |
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| Life Stage | April | May | June | July | August | Sept. |
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