The Great Basin spadefoot (Spea intermontana) is an amphibian in the family Scaphiopodidae. It is long and is usually colored gray, olive or brown. Great Basin spadefoot toads have adapted to life in dry habitats. They use the hard, keratinized spade on each foot to dig a burrow, where they spend long periods during cold and dry weather. They are opportunistic hunters and will eat anything they can subdue. While their tadpoles have numerous predators, adults are able to produce skin secretions that deter enemies.
Identification
The Great Basin spadefoot ranges from long. It is usually gray, olive or brown colored. Gray streaks outline an hourglass-shaped marking on the back. The skin is smooth compared with the bumpy skin of the true toads in the genus Bufo. There is a spade present on the inside of each hind foot; it has sharp edges and is wedge-shaped. A glandular boss is present between the eyes. Eyes are catlike; pupils are vertical in bright light and round at night. Dark brown spots are present on each upper eyelid.
Habitat and distribution
The natural habitats of the Great Basin spadefoot include pinyon-juniper, ponderosa pine, and high elevation (up to ) spruce-fir forests, semidesert shrubland, sagebrush flats, temperate grasslands, and deserts. They are present in agricultural areas as well. The Great Basin Spadefoot can be found from southern British Columbia through the eastern portions of Washington and Oregon and in southern Idaho. Their range extends throughout all of Nevada and into most of Utah; they are also present in small areas in California, Arizona, Colorado, and Wyoming.
Reproduction
Breeding
Breeding is explosive, meaning that large congregations of individuals assemble and mate with each other. Adults are terrestrial and must migrate to breeding sites. Breeding may take place in permanent or temporary water sources such as springs, sluggish streams, and manmade reservoirs during the months of April through July. Spring rains usually provide the stimulus for males to emerge from their burrows for breeding, although unlike other spadefoots (Scaphiopus spp.), Great Basin spadefoots do breed during periods of no rainfall. The stimulus for breeding in the absence of rain is unknown. Males move to breeding waters first and begin vocalizing. Once females arrive, there is a race to mate with as many others as possible, and physical contests between males are common.
Females usually lay 300–500 eggs contained in a sticky gel, but have been reported lay as many as 1000 eggs in captivity. The female deposits her fertilized eggs in several different locations within the breeding water: on vegetation, rocks, bottom of the pool, or anything else that anchors the eggs. After mating, females return to their burrows. Males stay at the breeding pool and continue vocalizing until females stop arriving (presumably because all females in the vicinity have mated); then the males also return to their burrows.
Development
Eggs hatch in 2 to 4 days, and the tadpole development and metamorphosis is complete within 4 to 8 weeks, depending upon temperature, food quality, and food quantity. Developing rapidly helps Great Basin spadefoots avoid desiccation and consequent death in their arid environment.
Young morphs (metamorphosed preadults) are small, about 0.8 inch (19 mm) in length on average. They have high surface-to-volume ratios; therefore, they are highly susceptible to desiccation and seek shade cover immediately after emerging from breeding pools. They grow, by about 110% in length and 1,100% in mass over 3 months under laboratory conditions. Tadpoles may be carnivorous or herbivorous, depending on environmental conditions. Different larval diets are associated with different morphological characteristics.
Behavior
Diet
Adult spadefoots are opportunistic carnivores. Adults have been shown to eat arthropods from the taxa Coleoptera, Diptera, Hemiptera, Hymenoptera, Lepidoptera, Neuroptera, Orthoptera, Trichoptera, Collembola, and Araneae. Ants and beetles are their most common prey. Feeding seems to be generalized and opportunistic; the toads will eat anything they can subdue.
Adults hunt in spring and summer, but only at night or during light rains. Spadefoot tadpoles are dimorphic. Within a cohort, some tadpoles have large mouthparts, while others have much smaller mouthparts. As well as consuming other types of food, large-mouthed individuals are cannibalistic, swallowing other tadpoles whole.