Plains Spadefoot Toad. Spea bombifrons

Description: Adult: Head and body length 35-60 mm. A robust, thick- bodied frog with relatively short limbs and a short, blunt snout. Eyes large and protruding, with vertical pupils. Tympanum small. A prominent boss present between the eyes. No enlarged parotoid glands. Dorsum of body covered with small to moderate-sized scattered tubercles. Digits short, hind feet partially webbed. A black, wedge-shaped spade present at the "heel." General colour ranges from various shades of brown to dull green, usually with four lighter stripes along the back. Tubercles tipped with yellow or orange. Belly white.

Larvae: Tadpoles reach a total length of 68 mm. Body widest behind the eyes, snout narrowed. Anus median, spiracle sinistral. Labial tooth rows usually 4/4. Light grey or brown above, lighter below. Caudal fins lightly pigmented. Tadpoles gulp air in areas where they are highly concentrated.

Variation: In some individuals the tip of the snout may be covered with black, keratinized skin. Females are slightly larger than males. Males have a blackish throat and keratinization on the fingers.

Natural history: In Alberta, active from late May until fall, but rarely seen outside of breeding periods. (In the United States, it is generally most active in the summer, in association with the rainy season). Typically found near permanent or temporary bodies of water, usually in areas of sandy or friable soil appropriate for burrowing. Uses the spades on the hind feet to dig backwards into soil to depths of almost one metre. It is able to supercool, which may decrease the depth to which it has to burrow in winter to protect itself from freezing. Feeds on small invertebrates, particularly nocturnal forms such as moths, ants and beetles. A sticky defensive secretion is exuded when molested. The larvae feed on plankton and detritus. Tadpoles may be cannibalistic, and may be able to withstand brief periods of almost total evaporation of their pools. Adults are seldom seen, but their presence in owl pellets suggests that they may be more widespread than generally recognized.

Reproduction: Breeds during spring or summer periods of rain, usually in vernal ponds or other temporary water bodies. Males call while floating in the water. Males hold females in pelvic amplexus. Eggs are laid in clusters of 10-250 and hatch in about 48 hours. Metamorphosis is completed about 21-40 days after hatching. Upon metamorphosis the spades are already well-formed and the young individuals are able to burrow.

Voice: A short, duck-like scream of 0.2-0.7 seconds duration.

Distribution: In Alberta, occurs at elevations up to 1,200 m, primarily in short-grass prairie, from the Montana and Saskatchewan borders north and west to the Red Deer River and Pincher Creek. Extralimitally, it occurs east to western Manitoba and south through the plains states to Chihuahua and eastern Arizona. Populations are probably continuous along the Missouri River to the Mississippi. An isolated population is known from extreme southern Texas and adjacent Mexico.

Conservation status: There is no evidence that this species has declined in recent years, but our knowledge of its populations within its limited range in Alberta is fragmentary. More evidence is needed to accurately assess its conservation status.

Remarks: Tadpoles may be preyed upon by aquatic arthropods. In order to survive the winter, spadefoots must locate sources of moisture in their arid surroundings. They burrow downward until they locate a damp resting spot, and have been found at depths of almost one metre. Collins (1990) places this species in the genus Spea, although Conant and Collins (1991) retain it in Scaphiopus. We have placed this species in the genus Spea following current usage (Wiens and Titus 1991, Collins 1997).

Significant references: Black 1970a; Bragg 1941,1944, 1965; Bragg and Bragg 1959; Farrar and Hey 1998; Hoyt 1960; Klassen 1990, 1998; Lauzon and Balagus 1998; Lewin 1963a; Moore 1952; Morlan and Matthews 1992; Nero 1959; Pfennig et al. 1993; Seymour 1973; Swanson and Graves 1995; Tanner 1939; Trowbridge 1941,1942.