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HERPS OF THE SOUTHEAST VIRTUAL WALK
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Stop #27: Overflow National Forest, AR
Featured Herp: Eastern Spadefoot Toad (Scaphiopus holbrookii)

 

Species account from: The Amphibians and Reptiles of Georgia. J. Jensen and C. Camp (eds.), University of Georgia Press, Athens, GA. 2008.

spadefoot toads mating

Description

The Eastern Spadefoot is a robust, relatively smooth-skinned “toad” that reaches a body length of up to 2.8 in (71 mm). The signature character of the genus Scaphiopus is the dark shovel-shaped protrusion on the inside of each hind foot. Compared to toads in the genus Bufo, the “warts” on spadefoots are less conspicuous, as are the enlarged glands (called parotoids)behind the eyes. The pupil of the eye in spadefoots is vertical, compared to horizontal in other toads and frogs.

geographic distribution

Coloration in spadefoots varies from very dark brown or nearly black to gray to olive. Usually two yellow lines run from the eyes down the sides of the back, often suggesting the shape of a lyre. Mature males have black pads on their thumbs and inner toes. Tadpoles reach total lengths of nearly 2 in (51 mm), and are dark brown to bronze in color, with a clear tail fin and no markings on the tail muscle. Tadpoles may metamorphose within three weeks after hatching, usually at a small body size of only 0.4-0.6 in (10-15 mm).

Taxonomy and Nomenclature

Also called “storm toads” because they are seen at times of flooding rains, spadefoots are Georgia’s sole representative of the family Pelobatidae. The genus name (Scaphiopus) is derived from the Greek words for shovel and foot. The name holbrookii honors John Edwards Holbrook, who is known as “the father of North American herpetology.” Two subspecies of the Eastern Spadefoot were once described, the Eastern Spadefoot (S. h. holbrookii) and Hurter’s Spadefoot (S. h. hurteri). Each has now been elevated to full species status, and only the Eastern Spadefoot is found in Georgia.

Habitat and Distribution

Spadefoots occur in a variety of habitats throughout Georgia, although they appear to be more common on the Coastal Plain than in provinces above the Fall Line. Adults are explosive breeders that use ephemeral wetlands, including pastureland pools, Carolina bays, and roadside ditches. The most important component of the terrestrial habitat may be the soil type; these toads prefer loose, well-drained sandy soils in which they can burrow. Spadefoots often inhabit relatively dry terrestrial habitats and can be found in pastures and farmland, pine plantations, forested lowlands, and coastal dunes.

Reproduction and Development

Unlike most species of amphibians that tend to breed seasonally, spadefoots may breed in any month of the year as long as the temperature is above 45° F (7° C). The primary cue for breeding is very heavy rain, often two in (51 mm) or more. Breeding choruses are most common at night but can occur in daylight. Female spadefoots lay strings of 2,500 or more eggs attached to twigs, vegetation, or leaves near the water surface. Egg and larval development is temperature dependent and may be extremely rapid. Eggs laid in summer months may hatch within 24 hours; in winter hatching may take four-seven days. After hatching tadpoles continue development for one-four days before initiating feeding. Initially the hatchlings may feed on plankton suspended in the water column, but after the teeth are fully developed, the tadpoles begin feeding on the film of material on surfaces of submerged vegetation and debris. Compared to tadpoles of other frog and toad species, spadefoot tadpoles are voracious feeders that eat anything they can catch. As tadpoles develop and grow, thousands of individuals may congregate in schools that measure dozens of feet long, several feet wide, and up to a foot deep. Spadefoot tadpoles are the locusts of temporary ponds, their schools moving throughout a pond, constantly feeding on suspended and surface materials, as well as on smaller animals, amphibian eggs, and even other spadefoot tadpoles. The larval period is approximately three weeks in summer and two months in late winter and spring. Adults reach maturity in two to three years, although some males may reproduce as 1-yr olds.

Habits

The Eastern Spadefoot may be the epitome of a secretive amphibian species. Individuals spend much of the year 2-12 in (5-30 mm) underground in burrows, often for weeks at a time. They generally emerge only on warm, humid or rainy nights and tend to be more active in the spring and fall. The diet of spadefoots includes beetles, ants, spiders, flies, caterpillars, and millipedes. Although it has not been studied in Georgia, in Florida spadefoots have a fairly small home range (108 sq ft, or 10 m2), in which they are likely to stay for years. After breeding, adults tend to migrate back to their burrows, which may be > 440 yd (400 m) from the breeding habitat. If the eggs and tadpoles do not die due to cold or early pond drying, then tens or even hundreds of thousands of newly metamorphosed toadlets can be produced from a single wetland. Observations of the “mass movements” of thousands of recently metamorphosed spadefoots may be one source of the phrase “raining frogs and toads.” The skins of these frogs are toxic to many predators. Even so, juveniles and adults may be preyed upon by raccoons, some snake species, particularly hognose snakes (genus Heterodon), grackles and other birds; the tadpoles are eaten by aquatic insects and salamanders. Average annual survivorship of adults is approximately 75%.

Status and Conservation

The Eastern Spadefoot has no special legal status in Georgia. Tiny ephemeral wetlands are largely unprotected and have incurred substantial historical losses. In addition, the terrestrial habitat requirements of spadefoots make them vulnerable to habitat fragmentation as well as increased urbanization. Young toadlets especially are unable to burrow in hardpan, gravel, or thick sod. Furthermore, road mortality of individuals migrating to and from breeding sites can be high.

Selected References

Hansen, K. L. 1958. Breeding pattern of the Eastern Spadefoot Toad. Herpetologica 14:57-67.

Jansen, K. P., A. P. Summers, and P. R. Delis. 2001. Spadefoot toads (Scaphiopus holbrookii holbrookii) in an urban landscape: effects of nonnatural substrates on burrowing in adults and juveniles. Journal of Herpetology 35:141-145.

Neill, W. T. 1957. Notes on metamorphic and breeding aggregations of the Eastern Spadefoot, Scaphiopus holbrooki (Harlan). Herpetologica 13: 185-187.

Pearson, P. G. 1955. Population ecology of the spadefoot toad, Scaphiopus h. holbrooki (Harlan). Ecological Monographs 25:233-267.

Account author: David E. Scott

 
 
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