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Spea hammondiiWestern Spadefoot

By Emily Roberts

Geographic Range

Western spadefoot toads (Spea hammondii) are found in California and northern Baja California. They are found in the foothills of the Central Valley and Sierra Nevada foothills (up to 1,385 m). They are also found starting south of Monterey Bay through southern California into Baja California. Western spadefoot toads used to be common in Los Angeles but have gone extinct in the area. They are still found in San Diego, Orange, and Riverside counties. (McGinnis and Stebbins, 2012)

Habitat

Western spadefoot toads are usually found in grasslands, chaparral, scrub, and oak woodlands (from 0 to 1,410 m above sea level). They are typically found in areas where the soil is favorable for burrowing. Western Spadefoots prefer treeless habitats and areas where temporary pools of water form. They are also found along sandy, gravel washes and small seasonal streams. During dry seasons, they are typically only found buried. Western Spadefoots burrow about 1 m deep into loose soil to avoid extreme temperatures and lack of moisture. They are only found above ground at night, usually only from late winter to spring and fall. Western spadefoot toads also come above ground following thunderstorms. It is thought that tree cover plays an important role in where Western spadefoot toads choose to burrow. (Baumberger, et al., 2019; Lemm, 2006; McGinnis and Stebbins, 2012)

  • Aquatic Biomes
  • temporary pools
  • Range elevation
    0 to 1410 m
    0.00 to 4625.98 ft

Physical Description

Adult Western spadefoot toads are medium in size, with snout-vent lengths (SVLs) of 3.8 to 6.3 cm. They are olive or gray on their dorsal sides, with orange or red skin tubercles. Their ventral sides are white or gray, with no markings. Western spadefoot toads have smooth skin, and sometimes have a light stripe on their backs. Their eyes are pale gold, with vertical pupils. They have no cranial boss or ridge between their eyes. On the undersides of their hind feet, Western Spadefoots have wedge-shaped black "spades". These spades are prominent and serve as one of the key features used when identifying them.

Western spadefoot toads have strong, hoarse voices that are compared to the purr of a cat. Their call lasts a little longer than a second. Western spadefoot toad larvae (or tadpoles) can be as large as 7.5 cm, but they are more commonly smaller. Larvae have dark brown, gray, or greenish black dorsal sides and cream or silvery ventral sides. They are also described as having copper iridescence. Their tail fins are usually olive, pale yellow, or copper. Larvae also have a 5/5 labial tooth row formula. (Lemm, 2006; McGinnis and Stebbins, 2012)

  • Sexual Dimorphism
  • sexes colored or patterned differently
  • Range length
    3.8 to 6.3 cm
    1.50 to 2.48 in

Development

Larval transformation occurs in late spring and summer. Tadpoles take 30 to 80 days to metamorphose. This metamorphosis is dependent on water temperature and the longevity of ephemeral pools. Tadpoles filter feed or feed on algae. (Groff, et al., 2012; Lemm, 2006; McGinnis and Stebbins, 2012)

Reproduction

Males use a distinct mating call to attract mates. This mating call is distinctly trilled, but varies slightly by individual location. (McGinnis and Stebbins, 2012)

Breeding takes place from January to June and is dependent on water – without pooled water, they will not breed at all. Western spadefoot toads will breed during different periods if the conditions for breeding are right. Females lay up to 500 eggs per year, laid in cylindrical clusters of 10 to 42. Eggs are attached to vegetation and hatch about a week after fertilization. Metamorphosis from tadpoles to adults takes 30 to 80 days, and occurs in late spring and summer. The length of metamorphosis is dependent on water temperature and longevity of ephemeral pools. Tadpoles filter feed or feed on algae while they are developing. (Groff, et al., 2012; Lemm, 2006; McGinnis and Stebbins, 2012)

  • Breeding interval
    Western Spadefoots breed when pooled water is present.
  • Breeding season
    Western Spadefoots typicaly breed from January to June.
  • Average number of offspring
    500
  • Average time to hatching
    1 weeks
  • Range age at sexual or reproductive maturity (female)
    1 to 2 years
  • Range age at sexual or reproductive maturity (male)
    1 to 2 years

Beyond the laying of eggs in suitable areas, there is no known parental investment in western spadefoot toads.

  • Parental Investment
  • no parental involvement

Lifespan/Longevity

Most western spadefoot toads live to about 12 years, reaching sexual maturity after 3 years. Predation accounts for most of their mortality. (Lannoo, 2005)

Behavior

Western spadefoot toads are only active at night, when they leave their burrows. They will forage around for food during this time. Western spadefoot toads bury themselves in up to 1 m of loose soil during the day. This helps them avoid extreme temperatures and low moisture levels. During the dry season, western spadefoot toads stay underground both day and night. They also congregate at favorable burrowing sites. These sites are usually far away from breeding areas. They produce a peanut-smelling secretion when handled. This secretion can cause skin irritation or hay fever-like symptoms. Males often call while floating or swimming on the edge of pools of water. They call from areas where they are more hidden. (Groff, et al., 2012; Lemm, 2006; McGinnis and Stebbins, 2012)

Home Range

Little is known about the home range size of western spadefoot toads.

Communication and Perception

Western spadefoot toad calls are loud and short, typically lasting less than one second. These calls are usually described as a snore-like “kwalk”. Male western spadefoot toads usually call while floating on the water. Western spadefoot toads do not have a release call. Listen to several western spadefoot calls here: http://www.californiaherps.com/frogs/pages/s.hammondii.sounds.html. (Lemm, 2006)

Food Habits

Adult western spadefoot toads are carnivorous. Their diet consists of insects, worms, and other invertebrates. They usually eat after rains that soak the ground, since that is when the organisms they eat appear most. Western spadefoot tadpoles are opportunistic feeders, so they both filter feed and feed on algae. (Lannoo, 2005; Lemm, 2006; McGinnis and Stebbins, 2012)

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

Predation

Western spadefoot tadpoles are preyed upon by larval California tiger salamanders (Ambystoma californiense), American bullfrogs (Lithobates catesbeianus), garter snakes (genus Thamnopis), racoons (Procyon lotor), and some duck species (family Anatidae). They are also eaten by various other predators when their pools dry up and they are more exposed. Adult western spadefoot toads serve as prey to several amphibians, reptiles, birds, and mammals. Two-striped garter snakes (Thamnophis hammondii) and American bullfrogs have been documented preying on adult western spadefoot toads. (Ervin and Cass, 2007)

Ecosystem Roles

Western spadefoot toads share their habitats with other pool-breeding organisms, such as California tiger salamanders (Ambystoma californiense), Pacific treefrogs (Pseudacris regilla), western toads (Anaxyrus boreas), and American bullfrogs (Lithobates catesbeianus). They also share the water with several types of introduced fish, such as mosquitofish (Gambusia affinis), green sunfish (Lepomis cyanellus), and several bullhead species (Ameiurus). These fish are found in breeding pools after they are introduced or washed into the pools. These fish (mosquitofish in particular) have been observed feeding on western spadefoot toads. Western spadefoot toad larvae serve as prey for California tiger salamanders. It has been found that the western spadefoot toads that were larvae in pools containing California tiger salamanders were consistently larger than toads that were not. There are no known parasites of western spadefoot toads, but polystomatid monogenean trematode parasites are known to affect other spadefoot toads. (Lannoo, 2005)

Economic Importance for Humans: Positive

There are no known positive economic effects of western spadefoot toads on humans.

Economic Importance for Humans: Negative

Western spadefoot toads produce a skin secretion to deter predators. This secretion smells of peanuts and exposure to it can cause a runny nose and watery eyes in humans, along with a burning sensation. (Lannoo, 2005)

Conservation Status

It is estimated that 80% of western spadefoot toad habitat south of Ventura County has been lost. Habitats in the central valley have also been lost due to urban and agricultural development. Several breeding sites have been impacted by the range expansion of American bullfrogs (Lithobates catesbeianus), which has impacted western spadefoot toad populations in turn. Introduced mosquitofish (Gambusia affinis) in vernal pools also threaten western spadefoot toad populations. Collection or possession of the western spadefoot toads is illegal without proper permits.

Western spadefoot toads are listed as near threatened on the IUCN Red List and have no special status on the U.S. Federal List, CITES, or the State of Michigan List. (Lannoo, 2005; Lemm, 2006; McGinnis and Stebbins, 2012)

Other Comments

Western spadefoot toads were previously known as Hammond’s spadefoot toads and their scientific name was previously Scaphiopus hammondii. (Lannoo, 2005)

Contributors

Emily Roberts (author), California State University, San Marcos, Tracey Brown (editor), California State University, San Marcos, Galen Burrell (editor), Special Projects.

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

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.

ectothermic

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

fertilization

union of egg and spermatozoan

forest

forest biomes are dominated by trees, otherwise forest biomes can vary widely in amount of precipitation and seasonality.

fossorial

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

insectivore

An animal that eats mainly insects or spiders.

internal fertilization

fertilization takes place within the female's body

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.

poisonous

an animal which has a substance capable of killing, injuring, or impairing other animals through its chemical action (for example, the skin of poison dart frogs).

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

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

Baumberger, K., M. Eitzel, M. Kirby, M. Horn. 2019. Movement and habitat selection of the western spadefoot (Spea hammondii) in southern California.. Plos One, 14/10: 1-16.

Ervin, E., T. Cass. 2007. Spea hammondii (Western Spadefoot). Reproductive Pattern. [demonstrated to be an opportunistic breeder, not an explosive breeder as some outdated literature may state]. Herpetological Review, 38/2: 196-197.

Groff, L., W. Duffy, S. Kahara, S. Chapin. 2012. Temporally irregular breeding of western Spadefoot toads (Spea hammondii) in managed wetlands. Northwestern Naturalist, 93/1: 79-83.

Lannoo, M. 2005. The Conservation Status of United States Species. Berkeley and Los Angeles, California: University of California Press.

Lemm, J. 2006. Field Guide to Amphibians and Reptiles of the San Diego Region. Berkeley and Los Angeles, California: University of California Press.

McGinnis, S., R. Stebbins. 2012. Field Guide to Amphibians and Reptiles of California. Berkeley and Los Angeles, California: University of California Press.

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