The plains spadefoot is a small toadlike amphibian with large, protruding eyes. The pupils of the eyes are vertical and elliptical. The hind legs are short, and the underside of each hind foot has a distinct, wedge-shaped spade, hence its name. The overall color ranges from gray to tan to brown; sometimes a greenish cast is present. A number of irregular dark brown markings are usually present on the back and hind legs. There may be 2 or 4 faint, light stripes on the back. The belly is white. Small, round “warts,” often red, are usually on the back and sides.
The male's call is an extended rasping or nasal “garvank” or "waaik" that is repeated at intervals of one-half to one second.
Spadefoots are known to produce skin secretions that can be noxious to other animals. When handling a spadefoot, it is best to avoid touching your face or eyes until you have washed your hands.
Similar species: The eastern spadefoot, which in our state occurs only in eastern counties along the Mississippi River and in the southeastern Missouri Bootheel region, is distinguished by the absence of a raised area (boss) between the eyes and by having a sickle-shaped spade at the base of each hind foot.
The North American spadefoot family is represented by two genera, Scaphiopus and Spea, and only two of them occur in Missouri. Spadefoots, often called spadefoot toads, are not true toads (family Bufonidae), although they resemble toads in general appearance and habits. The name "spadefoot" comes from a special tubercle on the hind feet that is shaped like a spade and is used for digging into sand and soil; spadefoots are highly adapted for living underground, and they are explosive breeders in ephemeral (temporary, seasonal) pools. They have smoother skin than true toads (genus Anaxyrus), and the pupils of their eyes are vertical.
Note that another species, Hurter’s spadefoot (Scaphiopus hurterii), has not been found in Missouri, but it could possibly one day be found within our borders. Its range is to the southwest of our state, and it extends into north-central and northwestern Arkansas. It is a secretive species but an explosive breeder. In Missouri, it would most likely be found on nights with heavy rainfall along the southern and southwestern border with Arkansas and Oklahoma, especially in sandy areas within river floodplains. Its range would likely not overlap with our other spadefoot species. To date, however, the Hurter’s spadefoot has not been found in Missouri.
Adult length (snout to vent): 1½ to 2 inches; occasionally to 2½ inches.
Occurs in counties along the Missouri River, in floodplain habitats from St. Louis to the northwestern corner of the state.
Habitat and Conservation
The plains spadefoot is primarily a species of the Great Plains, where it lives in grassland or open floodplain environments.
In Missouri, which is part of the species' easternmost range, the plains spadefoot lives in the loose, sandy soils of the Missouri River floodplain and its flooded fields.
By day it hides in burrows in sandy soil. It emerges at night to forage and breed, especially after heavy rains. It digs its own burrows, backward, using the wedge-shaped spade on the hind feet.
Food
Earthworms and a variety of insects make up the bulk of the plains spadefoot’s diet. A specimen from Jackson County was found to have eaten a mole cricket (Gryllotalpidae).
Status
Taxonomy: Often called spadefoot toads, spadefoots are not true toads, nor are they true frogs, either. They’re named for a feature on the inner surface of their hind feet, a spadelike spur that helps them to dig their burrows.
Life Cycle
This species is an explosive breeder that appears suddenly in great numbers after warm, heavy rains. In Missouri, breeding usually takes place from early April through August, although some calling activity occurs in late March in warmer years.
Breeding may be completed in a few nights, in temporary pools in flooded fields or roadside ditches. A female can produce up to 2,000 eggs, which are usually attached to submerged plant material in small masses of 10–250. The eggs may hatch in a few days. Hatching time and development rate vary with temperature, food supply, and the amount of oxygen in the water. The time between hatching and metamorphosis can vary from 13 to 30 days.
Human Connections
Plains spadefoots have inspired a great deal of biological research. Among the many topics of interest are their adaptations for surviving in dry environments and in freezing temperatures. In addition to helping us better protect these and other animals, knowledge of these survival mechanisms may have applications for human health and medicine.
Ecosystem Connections
To survive in their particular environments, spadefoots have a greater tolerance to desiccation (drying out) than other amphibians native to North America. They may lose up to half of their water content and still survive. A study of plains spadefoots in South Dakota showed that young specimens can protect themselves from tissue damage due to freezing during extremely cold periods. Adults are known to dig up to 35 inches deep to avoid freezing temperatures.
A predator of insects, the plains spadefoot and a host of other small insectivores function to control the populations of the hosts of those creatures. Meanwhile, the frogs, and their own eggs and tadpoles, are eaten by larger predators.
