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Spea bombifronsplains spadefoot(Also: Sapo-de espuelas de las planicies)

By Tanya Dewey

Geographic Range

Plains spadefoot toads, Spea bombifrons, are native to the Nearctic region. Their North American range stretches from southern Alberta and Saskatchewan, Canada south to the panhandle and lower tip of Texas, and into northern Mexico. They range as far west as southeastern Arizona and east to Nebraska, western Missouri, and western Oklahoma. Their range seems to be expanding along the Missouri River floodplain and in southern Alberta and Saskatchewan. There are disjunct populations in southern Colorado, northeastern Mexico, southernmost Texas, and along the Arkansas River in Arkansas. (Alberta Government, 2002; Holman, 2003; LeClere, 2005; Sargeant, et al., 1993; Alberta Government, 2002; Cannatella and Bockstanz, 1999; Farrar and Hey, 2006; Holman, 2003; Lauzon, 1999; LeClere, 2005; Sargeant, et al., 1993)

Habitat

Plains spadefoot toads are found mainly in the arid grasslands of western North America. They are restricted to areas with loose soils for burrowing. They can also be found in savannas, loess hills, sandhills, and semi-desert and desert scrub. They are found in shallower summer burrows and deeper winter burrows throughout the year. Larvae require small, ephemeral ponds for development, such as cattle ponds, vernal pools, playa lakes, and flooded agricultural fields. Suitable ponds are difficult to find in habitats that plains spadefoot toads prefer. The soft, sandy soils they prefer for burrowing are also usually permeable to water. Because of this they also require proximity to areas where soils are less permeable and permit formation of temporary breeding pools. Juveniles burrow into soft mud along the ponds in which they developed or crawl into crevices in dried mud or under plant litter. (Cannatella and Bockstanz, 1999; Farrar and Hey, 2006; Lauzon, 1999; LeClere, 2005; McCormick, 2006)

  • Aquatic Biomes
  • lakes and ponds
  • temporary pools
  • Range elevation
    700 to 7500-8000 m
    2296.59 to ft

Physical Description

Plains spadefoot toads measure 38.1 to 63.5 mm (2 to 2.5 inches) in length, and weigh approximately 30 grams. Females tend to be slightly larger. They are brown or gray, sometimes with hints of green, and dark splotches or warts. On their dorsal and lateral surfaces are 4 vague stripes, with the middle two stripes sometimes forming an hourglass-like shape. Some have red or orange spots as well. Plains spadefoot toads are called "spadefoot" because of a welll-developed, sharp, spade-shaped and black tubercle on each of their rear feet. This is a bony extension of the metatarsal, covered with keratin that is used to burrow with the rear feet. There is a raised bone (or "boss") between their eyes, and their pupils are vertical, like those of cats. Adult, breeding males have a keratinous "nuptial pad" on their thumbs. (Alberta Government, 2002; Cannatella and Bockstanz, 1999; Farrar and Hey, 2006; Holmes, 1954; LeClere, 2005; McCormick, 2006; Sargeant, et al., 1993)

Plains spadefoot toads are not true toads (Bufonidae). They are members of a small, frog family, Pelobatidae. (Farrar and Hey, 2006; McCormick, 2006)

  • Sexual Dimorphism
  • female larger
  • sexes shaped differently
  • Average mass
    30 g
    1.06 oz
  • Range length
    38.1 to 63.5 mm
    1.50 to 2.50 in

Development

Plains spadefoot toad eggs usually hatch within two days of being laid. At 30 degrees Celsius eggs hatch in 20 hours. Tadpole development (time to metamorphosis) usually lasts 13 to 20 days, depending on ambient temperatures. In northern parts of the range, time to metamorphosis may be up to 60 days, with average times in Alberta being 21 to 34 days. Tadpoles reach up to 7 cm in length and have a dark olive/yellow color with irridescent highlights. Plains spadefoot toad larvae develop primarily in small, temporary ponds and larvae are tolerant of widely fluctuating and high water temperatures. They metamorphose rapidly, before breeding ponds evaporate. As members of the family Pelobatidae, plains spadefoot toads have one of the fastest development rates among amphibians. (Alberta Government, 2002; Cannatella and Bockstanz, 1999; Farrar and Hey, 2006; Sargeant, et al., 1993)

Reproduction

After heavy rains, males travel to breeding ponds and begin to call. Calls attract both males and females, with louder choruses attracting the most individuals. Calls are loud and harsh and can be heard up to 3 km away. In some areas of the southwest Spea bombifrons uses the same breeding ponds as other Spea species and hybridization has been documented in the laboratory. Mating calls act as reproductive isolating mechanisms in these circumstances. Two mating call types have been identified in plains spadefoot toads. Spea bombifrons has been observed calling at mating ponds at temperatures as low as 10.5°C. (Alberta Government, 2002; Cannatella and Bockstanz, 1999; Farrar and Hey, 2006; Lauzon, 1999; Sargeant, et al., 1993)

Plains spadefoot toads mate during or after heavy rains (from 2.5 to 10.4 cm). Times of rainfall vary with latitude, but in the center of the range of S. bombifrons, this is from May to August. Plains spadefoot toads live primarily on land, traveling to breeding ponds only to mate. They lay their eggs in temporary ponds created by the rain. These ponds are generally up to 1 meter in depth. They have been observed breeding in natural ponds, oxbow areas of rivers, and sloughs as well as irrigation and roadside ditches, flooded areas of playgrounds and constructions sites, and in flooded agricultural fields. Females lay up to 2,000 eggs, in masses of 10 to 250. Eggs fall to the pond bottom or are attached to vegetation or other submerged objects. Sexual maturity is reached in the second year after hatching. (Alberta Government, 2002; Cannatella and Bockstanz, 1999; LeClere, 2005; McCormick, 2006; Sargeant, et al., 1993)

  • Breeding interval
    Plains spadefoot toads may breed multiple times during a season, if conditions are good, or they may not breed in a year if conditions are poor.
  • Breeding season
    Plains spadefoot toads will breed after periods of sufficient rain between the months of May and August.
  • Range number of offspring
    2000 (high)
  • Range time to hatching
    2 to 3 days
  • Average age at sexual or reproductive maturity (female)
    2 years
  • Average age at sexual or reproductive maturity (male)
    2 years

After the eggs are deposited in a temporary pond, there is no further parental care. (Alberta Government, 2002; Cannatella and Bockstanz, 1999; Farrar and Hey, 2006; McCormick, 2006; Sargeant, et al., 1993)

  • Parental Investment
  • no parental involvement
  • pre-fertilization
    • provisioning
    • protecting
      • female

Lifespan/Longevity

The maximum lifespan of plains spadefoot toads is estimated at 13 years. (Farrar and Hey, 2006)

  • Typical lifespan
    Status: wild
    13 (high) years

Behavior

Plains spadefoot toads are nocturnal, emerging during humid nights to forage. During the day, they remain in their burrows. Plains spadefoot toads emerge less frequently and burrow more deeply during especially dry times, such as droughts or during summer. Burrows can be as deep as 1 meter. Because they rely on burrowing to protect them from dry conditions, plains spadefoot toads are restricted to areas with loose soils. Burrows are usually dug close to a plant or other object that provides shade at the entrance. In winter, plains spadefoot toads will burrow more deeply to avoid freezing temperatures. When from 2.5 to 10.4 cm of rain falls, these toads emerge from their burrows and migrate to breeding ponds. Lighter rains and snow melt will also attract smaller numbers of plains spadefoot toads from their burrows to congregate at temporary ponds. (Cannatella and Bockstanz, 1999; Holmes, 1954; Lauzon, 1999; McCormick, 2006)

  • Average territory size
    10 m^2

Home Range

Because plains spadefoot toads can survive long periods of time without food and remain inactive underground, they require little individual space. The average home range for plains spadefoot toads in Alberta is 10 square meters. Closely related eastern spadefoot toads (Spea holbrooki) have home ranges of 10.1 square meters, with male ranges being slightly larger than female ranges. Individuals have been recorded traveling 1.6 km to breeding sites and toadlets have been recorded 2 km from their natal ponds within weeks of metamorphosis. (Alberta Government, 2002)

Communication and Perception

Plains spadefoot toads have a mating call that is approximately 0.5 - 1.0 second in length and sounds similar to that of a mallard. This call, and another low, rough call, both act as mating calls. A male's mating call can be heard as far as 3 km away. (McCormick, 2006)

Food Habits

Plains spadefoot toad tadpoles can develop into carnivorous "trophic morphs" or omnivorous "trophic morphs." Carnivorous tadpoles develop faster than omnivorous tadpoles and eat other spadefoot toad tadpoles and invertebrates. Cannibalism in breeding ponds is common. Omnivorous tadpoles eat organic matter, especially algae. (Farrar and Hey, 2006)

Adult plains spadefoot toads eat small invertebrates, such as hymenopterans, flies, moths, beetles, spiders, and stink bugs. (Farrar and Hey, 2006)

  • Animal Foods
  • amphibians
  • insects
  • terrestrial non-insect arthropods
  • terrestrial worms
  • Plant Foods
  • algae

Predation

The cryptic coloration and burrowing habits of Spea bombifrons may protect many individuals from predation. They also have noxious skin secretions that may deter predators. Tadpoles gather in large feeding aggregations when they detect a predator, which may protect some individuals. (Farrar and Hey, 2006; Lauzon, 1999)

Hydrophilid beetle larvae (Hyrus triangularis), crustaceans (Apus), and other spadefoot toad tadpoles prey on tadpoles. Adults may be preyed on by barn owls (Tyto alba), Swainson's hawks (Buteo swainsoni), prairie rattlesnakes (Crotalus viridis), and burrowing rodents. (Farrar and Hey, 2006; Lauzon, 1999)

  • Anti-predator Adaptations
  • cryptic

Ecosystem Roles

Plains spadefoot toads affect populations of their invertebrate prey. They also share breeding ponds with other spadefoot toad species (Spea) and with Great Plains toads (Anaxyrus cognatus). Plains spadefoot toad tadpoles will eat Anaxyrus cognatus tadpoles where they share breeding ponds. They also share breeding ponds with Woodhouse's toads, Anaxyrus woodhousii woodhousii. (Farrar and Hey, 2006; McCormick, 2006)

Plains spadefoot toads will outcompete Mexican spadefoot toads (Spea multiplicata) for fairy shrimp (Anostraca) where they co-occur. (Farrar and Hey, 2006)

Tadpoles are sometimes infected with Saprolegnia fungus. Adults have been found with intradermal mites (Acari) and may carry a monogean parasite, Pseudodiplorchis americanus. (Farrar and Hey, 2006)

Commensal/Parasitic Species

Economic Importance for Humans: Positive

Plains spadefoot toads are important members of the healthy ecosystems in which they live.

Economic Importance for Humans: Negative

There is no known negative economic importance for humans.

Conservation Status

Plains spadefoot toad populations seem to be healthy, for the most part. Local population declines are often the result of lack of breeding during drought years. In Alberta they are on the "blue list" of species at risk of decline because of non-viable population levels in the province. Plains spadefoot toads may be expanding their range in North America but local populations may be threatened by development that endangers breeding ponds, such as wetland draining and conversion of land to agriculture. The use of pesticides, herbicides, and the presence of other pollutants in water may also be a threat to these frogs. (Lauzon, 1999; McCormick, 2006)

Contributors

Tanya Dewey (author), Animal Diversity Web.

Glossary

Nearctic

living in the Nearctic biogeographic province, the northern part of the New World. This includes Greenland, the Canadian Arctic islands, and all of the North American as far south as the highlands of central Mexico.

World Map

acoustic

uses sound to communicate

agricultural

living in landscapes dominated by human agriculture.

bilateral symmetry

having body symmetry such that the animal can be divided in one plane into two mirror-image halves. Animals with bilateral symmetry have dorsal and ventral sides, as well as anterior and posterior ends. Synapomorphy of the Bilateria.

carnivore

an animal that mainly eats meat

chaparral

Found in coastal areas between 30 and 40 degrees latitude, in areas with a Mediterranean climate. Vegetation is dominated by stands of dense, spiny shrubs with tough (hard or waxy) evergreen leaves. May be maintained by periodic fire. In South America it includes the scrub ecotone between forest and paramo.

chemical

uses smells or other chemicals to communicate

cryptic

having markings, coloration, shapes, or other features that cause an animal to be camouflaged in its natural environment; being difficult to see or otherwise detect.

desert or dunes

in deserts low (less than 30 cm per year) and unpredictable rainfall results in landscapes dominated by plants and animals adapted to aridity. Vegetation is typically sparse, though spectacular blooms may occur following rain. Deserts can be cold or warm and daily temperates typically fluctuate. In dune areas vegetation is also sparse and conditions are dry. This is because sand does not hold water well so little is available to plants. In dunes near seas and oceans this is compounded by the influence of salt in the air and soil. Salt limits the ability of plants to take up water through their roots.

detritus

particles of organic material from dead and decomposing organisms. Detritus is the result of the activity of decomposers (organisms that decompose organic material).

ectothermic

animals which must use heat acquired from the environment and behavioral adaptations to regulate body temperature

external fertilization

fertilization takes place outside the female's body

fertilization

union of egg and spermatozoan

fossorial

Referring to a burrowing life-style or behavior, specialized for digging or burrowing.

heterothermic

having a body temperature that fluctuates with that of the immediate environment; having no mechanism or a poorly developed mechanism for regulating internal body temperature.

insectivore

An animal that eats mainly insects or spiders.

iteroparous

offspring are produced in more than one group (litters, clutches, etc.) and across multiple seasons (or other periods hospitable to reproduction). Iteroparous animals must, by definition, survive over multiple seasons (or periodic condition changes).

metamorphosis

A large change in the shape or structure of an animal that happens as the animal grows. In insects, "incomplete metamorphosis" is when young animals are similar to adults and change gradually into the adult form, and "complete metamorphosis" is when there is a profound change between larval and adult forms. Butterflies have complete metamorphosis, grasshoppers have incomplete metamorphosis.

motile

having the capacity to move from one place to another.

native range

the area in which the animal is naturally found, the region in which it is endemic.

nocturnal

active during the night

oviparous

reproduction in which eggs are released by the female; development of offspring occurs outside the mother's body.

polygynandrous

the kind of polygamy in which a female pairs with several males, each of which also pairs with several different females.

scrub forest

scrub forests develop in areas that experience dry seasons.

seasonal breeding

breeding is confined to a particular season

sedentary

remains in the same area

sexual

reproduction that includes combining the genetic contribution of two individuals, a male and a female

tactile

uses touch to communicate

temperate

that region of the Earth between 23.5 degrees North and 60 degrees North (between the Tropic of Cancer and the Arctic Circle) and between 23.5 degrees South and 60 degrees South (between the Tropic of Capricorn and the Antarctic Circle).

terrestrial

Living on the ground.

tropical savanna and grassland

A terrestrial biome. Savannas are grasslands with scattered individual trees that do not form a closed canopy. Extensive savannas are found in parts of subtropical and tropical Africa and South America, and in Australia.

savanna

A grassland with scattered trees or scattered clumps of trees, a type of community intermediate between grassland and forest. See also Tropical savanna and grassland biome.

temperate grassland

A terrestrial biome found in temperate latitudes (>23.5° N or S latitude). Vegetation is made up mostly of grasses, the height and species diversity of which depend largely on the amount of moisture available. Fire and grazing are important in the long-term maintenance of grasslands.

visual

uses sight to communicate

References

Alberta Government, 2002. "Plains Spadefoot" (On-line). Alberta Government Sustainable Resource Development. Accessed April 09, 2006 at http://www3.gov.ab.ca/srd/fw/amphib/ps.html.

Cannatella, D., L. Bockstanz. 1999. "Plains Spadefoot" (On-line). Herps of Texas. Accessed April 09, 2006 at http://www.zo.utexas.edu/research/txherps/frogs/spea.bombifrons.html.

Farrar, E., J. Hey. 2006. "Spea bombifrons" (On-line). Amphibiaweb. Accessed September 19, 2006 at http://www.amphibiaweb.org/cgi-bin/amphib_query?query_src=aw_search_index&table=amphib&special=one_record&where-genus=Spea&where-species=bombifrons.

Holman, J. 2003. Fossil Frogs and Toads of North America. Bloomington and Indianapolis: Indiana University Press.

Holmes, S. 1954. The Biology of the Frog. New York: The MacMillan Company.

Lauzon, R. 1999. "State of Plains Spadefoot in Alberta" (On-line). Accessed April 09, 2006 at http://www3.gov.ab.ca/srd/FW/status/reports/pdf/spadefoot.pdf.

LeClere, J. 2005. "Plains Spadefoot" (On-line). Iowa Herpetology. Accessed April 09, 2006 at http://www.herpnet.net/Iowa-Herpetology/amphibians/frogs_toads/plainsSpadefootToad.html.

McCormick, C. 2006. "Spea bombifrons" (On-line). Amphibiaweb. Accessed September 19, 2006 at http://amphibiaweb.org/cgi/amphib_query?where-genus=Spea&where-species=bombifrons&account=amphibiaweb.

Rostand, J. 1934. Toads and Toad Life. London: Methuen & Co. Ltd..

Sargeant, A., R. Greenwood, M. Sovada, T. Shaffer. 1993. "Plains Spaidfoot, Spea Bombifrons" (On-line). Accessed April 09, 2006 at http://www.npwrc.usgs.gov/narcam/idguide/speab.htm.

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