Anaxyrus

Features
By Kirsten Kinder

Diversity

Anaxyrus (previously known as Bufo ) is a genus of true toads within the family Bufonidae . The genus Anaxyrus includes 25 species distributed throughout North and Central America. Species in the genus Anaxyrus are common in a variety of environments, including temperate, tropical, and subtropical forests, as well as grasslands and deserts. Some species, like American toads ( Anaxyrus americanus ) and Fowler's toads ( Anaxyrus fowleri ), have broad ranges, whereas other species, such as Dixie Valley toads ( Anaxyrus williamsi ), are endemic to small stretches of suitable habitat.

Geographic Range

Species in the genus Anaxyrus are found throughout North and Central America, as far north as sub-arctic Canada and as far south as southern Mexico. They can live at a variety of altitudes ranging from sea level to almost 10,000 feet above sea level. In many cases, especially in the southwestern United States, several species in the genus Anaxyrus have overlapping ranges. This has lead to zones of hybridization between sympatric species.

Habitat

Species in the genus Anaxyrus occupy a diverse range of habitats and geographical areas, including deserts, wetlands, plains, forests, and montane regions. Although they vary in habitat selection, all species depend on sources of freshwater, especially during breeding season. The distribution of Anayrus species across a landscape is partially dependent on the distribution of permanent and ephemeral sources of water.

  • Aquatic Biomes
  • lakes and ponds
  • rivers and streams
  • coastal

Systematic and Taxonomic History

Anaxyrus species were previously included in the genus Bufo , which had comprised nearly all true toad species. However, as of 2006, many Bufo species have been reclassified as members of newly established or formerly recognized genera. The genus Anaxyrus currently includes many of the true toads native to North America.

Physical Description

Toads in the genus Anaxyrus are similar in morphology. Adults typically range from 50.8 to 76.2 mm in length, with stout bodies, whitish ventral coloration, and brown dorsal coloration, often with darker patches color dispersed along their heads, backs, sides, and limbs. Some species have more colorful dorsal patches, such as the yellow coloration of North American green toads ( Anaxyrus debilis ) or Sonoran green toads ( Anaxyrus retiformis ) or the orange and red coloration of Dixie Valley toads ( Anaxyrus williamsi ) or red-spotted toads ( Anaxyrus punctatus ). In general, females are slightly larger than males, but they are similar in color. Juveniles are also similar in color, though smaller than adults. Anaxyrus species have two large parotoid glands - one behind each eye - that secrete bufotoxins and serve as a defense from predation.

  • Sexual Dimorphism
  • female larger

Development

Toads in the genus Anaxyrus lay their eggs in or near sources of freshwater, often close to vegetation. Depending on the species, eggs hatch anywhere from 3 to 12 days after they are laid. Tadpoles remain in their natal pools as they undergo metamorphosis, which lasts between 40 and 70 days, depending on the species. As metamorphosis progresses, tadpoles develop hind legs and forelegs, and their gills and tails gradually reduce in size. Fully-developed toadlets may remain near their natal pools for several days or weeks, depending on the species. Local environmental factors can also influence the timing of toad development. The presence of predators, pollutants, and low water temperature has been associated with prolonged larval period and reduced body size upon completion of development. Adult Anaxyrus toads exhibit indeterminate growth and typically reach sexual maturity by the beginning of the next breeding season.

Reproduction

Anaxyrus toads reproduce in aquatic environments. The breeding periods of many species are triggered by local increases in precipitation. For species in temperate environments at higher latitudes, breeding often occurs in spring or early summer (between March and June). In contrast, species in arid environments at lower latitudes may breed in winter (around January) or opportunistically after heavy rainfall events, often between late spring and early fall (April to September).

Toads in the genus Anaxyrus are typically polygynandrous or polygynous. Males congregate at bodies of water and produce calls to attract mates by inflating their vocal sacs. Males use their forearms to mount females and grip them around the abdomen in a position called "amplexus". Females that are not receptive to mating may attempt to shake off mounted males, and several males may attempt to mount concurrently. During amplexus, females release batches of eggs that males fertilize externally.

Anaxyrus toads mate near bodies of freshwater, with males producing calls to attract mates. Females produce around 4,000 to 8,000 eggs, laying them in the water in one or two rows. Males grasp females from behind in a position known as "amplexus" and fertilize eggs externally. Eggs hatch anywhere from 3 to 12 days after they are fertilized, depending on the species. Tadpoles undergo metamorphosis, which typically takes between 40 and 70 days. Fully metamorphosed toadlets grow rapidly until they reach adult size, then exhibit slow growth rates throughout the rest of their life. Toads in the genus Anaxyrus reach sexual maturity 2 to 3 years after they are born.

Toads in the genus Anaxyrus exhibit parental investment beyond the act of mating. Males may select territories based on the level of vegetative cover, and quality of male territory can affect mate selection by females. Areas with vegetative cover may provide better protection against egg predation.

  • Parental Investment
  • pre-fertilization
    • provisioning
    • protecting
      • female

Lifespan/Longevity

Toads in the genus Anaxyrus can live to 10 years old or more, both in the wild and in captivity. The average lifespan is around 5 to 6 years. Many tadpoles and toadlets do not survive to adulthood, but mortality risk decreases as individuals get larger with age.

Behavior

Anaxyrus toads do not live in collective groups or exhibit any apparent social hierarchies; they typically only interact directly with conspecifics when breeding. For the most part, frogs crawl to move around, but they also hop to cover longer distances or escape threats.

Although Anaxyrus toads do not travel long distances, they exhibit small-scale, seasonal migrations between habitats for breeding and brumation (a state of prolonged reduction in metabolism, similar to hibernation in mammals). Brumation activity varies by species and by climate. Frogs burrow into sand, dirt, or mud to insulate themselves from harsher external temperatures. Many species, especially in temperate areas, brumate in the winter (starting between August and October) and emerge in spring (between March to May) to breed in freshwater habitats. Some species in arid environments brumate at other times of year, during particularly dry periods, and emerge when rainfall becomes more frequent. For some species, only short bursts of heavy rain are necessary to trigger breeding activity.

Communication and Perception

Anaxyrus toads communicate primarily using vocalizations, although tactile and chemical cues may also be important. Males attract mates by producing mating calls with their vocal sacs. Male Anaxyrus toads are the only ones that vocalize, often producing chirping or croaking calls depending on the species. When mating, male toads use their forearms to mount females and grasp their abdomens, in a position called "amplexus". The physical contact involved in amplexus stimulates mating females to lay their eggs. Olfaction may also play a role in finding and selecting mates. Anaxyrus toads produce sex-specific pheromones that may also communicate body condition or mating status. Toads also use chemicals to communicate to other species that they are unpalatable. When threatened, they secrete bufotoxins and volatile chemicals from specialized glands posterior to their eyes, called parotoid glands. The bufotoxins have an unpleasant taste and can have severe health effects if ingested.

Toads in the genus Anaxyrus perceive their surroundings using tactile, chemical, visual, and acoustic cues. Tadpoles have a lateral line system, which helps them detect changes in water pressure, such as those created by movement. Tadpoles also rely heavily on chemical signals to detect the presence of food and predators. Adults may also detect prey based on chemical cues, but they primarily identify predators and prey visually.

Food Habits

Toads are insectivores, opportunistically eating insects and other arthropods walking nearby. Prey items include earthworms (family Lumbricidae ), beetles (order Coleoptera ), crickets (order Orthoptera ), ants (family Formicidae ), spiders (order Araneae ), and various other arthropods. Anaxyrus toads are ambush predators, often waiting in one place and catching nearby prey by using swift tongue movements, called “zots”. In three months, a single toad can consume as many as 10,000 insects.

Predation

Predators of Anaxyrus toads include snakes (suborder Serpentes ), birds (class Aves ), racoons ( Procyon lotor ), and coyotes ( Canis latrans ). Tadpoles are also eaten by fish and some predatory arthropods, such as dragonfly larvae (order Odonata ) and predaceous diving beetles (family Dytiscidae ). Adult toads typically have mottled brown or grey coloration that serves as cryptic camouflage and helps them avoid detection. Although they often remain completely still in the presence of predators, they will flee or play dead if they are detected. Anaxyrus toads are also capable of producing bufotoxins from their parotoid glands, located just posterior to their eyes. Bufotoxins are unpalatable and can be toxic to some predators.

Ecosystem Roles

Toads in the genus Anaxyrus play important ecological roles as predators and prey. As opportunistic insectivores, they help control local arthropod populations. Both tadpoles and adult toads also serve as prey items for larger predators, including arthropods and fish (tadpole predators) as well as birds, snakes, and some mammals (adult toad predators).

Economic Importance for Humans: Positive

Toads can be economically beneficial to the agriculture industry by reducing insect pest populations. An individual American toad ( Anaxyrus americanus ) can consume up to 10,000 insects in a three-month period, and around 88% of the prey items toads consume are classified as agricultural pests. The presence of toads can reduce the need for pesticides, avoiding negative impacts on the environment and reducing costs for farmers.

  • Positive Impacts
  • controls pest population

Economic Importance for Humans: Negative

Toads in the genus Anaxyrus can negatively impact the health of humans and pets. Because they produce bufotoxins, toads can cause sever illness or death when ingested. Symptoms of exposure to bufotoxins include seizures, fainting, cardiac arrhythmia, and potentially death. The effects of bufotoxins are generally more severe for smaller animals, but can still be dangerous for adults and large pets.

Conservation Status

Nearly all 25 species of toads in the genus Anaxyrus are classified as Least Concern on the IUCN Red List. However, the Wyoming Toad ( Anaxyrus baxteri ) is considered extinct in the wild and several species are considered vulnerable or endangered, often with declining populations. Many southern species, such as Yosemite toads ( Anaxyrus canorous ), Railroad Valley toads ( Anaxyrus nevadensis ), black toads ( Anaxyrus exsul ), Amargosa toads ( Anaxyrus nelsoni ), Houston toads ( Anaxyrus houstonensis ), Dixie Valley toads ( Anaxyrus williamsi ), Hot Creek toads ( Anaxyrus monfontatus ), and arroyo toads ( Anaxyrus californicus ) have limited geographic ranges and are classified as vulnerable, endangered, or critically endangered due to habitat loss. Human developments have replaced large stretches of woodlands and wetlands that toads rely on for breeding and overwintering habitat. Water pollution is also a major threat to toad development and mortality. Pesticides, fertilizers, and other chemicals can affect the development of eggs and tadpoles, increasing the rate of mortality and the development of deformities that can impact adult fitness.

AmphibiaWeb

Encyclopedia of Life

Contributors

Kirsten Kinder (author), Colorado State University, Genevieve Barnett (editor), Colorado State University, Galen Burrell (editor), Special Projects, Tanya Dewey (editor), University of Michigan-Ann Arbor.

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

native range

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

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).

tropical

the region of the earth that surrounds the equator, from 23.5 degrees north to 23.5 degrees south.

terrestrial

Living on the ground.

freshwater

mainly lives in water that is not salty.

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.

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.

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.

forest

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

rainforest

rainforests, both temperate and tropical, are dominated by trees often forming a closed canopy with little light reaching the ground. Epiphytes and climbing plants are also abundant. Precipitation is typically not limiting, but may be somewhat seasonal.

mountains

This terrestrial biome includes summits of high mountains, either without vegetation or covered by low, tundra-like vegetation.

coastal

the nearshore aquatic habitats near a coast, or shoreline.

marsh

marshes are wetland areas often dominated by grasses and reeds.

swamp

a wetland area that may be permanently or intermittently covered in water, often dominated by woody vegetation.

bog

a wetland area rich in accumulated plant material and with acidic soils surrounding a body of open water. Bogs have a flora dominated by sedges, heaths, and sphagnum.

suburban

living in residential areas on the outskirts of large cities or towns.

agricultural

living in landscapes dominated by human agriculture.

riparian

Referring to something living or located adjacent to a waterbody (usually, but not always, a river or stream).

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.

indeterminate growth

Animals with indeterminate growth continue to grow throughout their lives.

polygynous

having more than one female as a mate at one time

polygynandrous

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

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).

seasonal breeding

breeding is confined to a particular season

sexual

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

fertilization

union of egg and spermatozoan

external fertilization

fertilization takes place outside the female's body

oviparous

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

motile

having the capacity to move from one place to another.

migratory

makes seasonal movements between breeding and wintering grounds

hibernation

the state that some animals enter during winter in which normal physiological processes are significantly reduced, thus lowering the animal's energy requirements. The act or condition of passing winter in a torpid or resting state, typically involving the abandonment of homoiothermy in mammals.

visual

uses sight to communicate

tactile

uses touch to communicate

acoustic

uses sound to communicate

chemical

uses smells or other chemicals to communicate

choruses

to jointly display, usually with sounds, at the same time as two or more other individuals of the same or different species

pheromones

chemicals released into air or water that are detected by and responded to by other animals of the same species

vibrations

movements of a hard surface that are produced by animals as signals to others

visual

uses sight to communicate

tactile

uses touch to communicate

acoustic

uses sound to communicate

vibrations

movements of a hard surface that are produced by animals as signals to others

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.

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).

carnivore

an animal that mainly eats meat

insectivore

An animal that eats mainly insects or spiders.

ectothermic

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

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.

References

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Allard, H. 1916. The song of Fowler’s toad (Bufo fowleri). Science , 44: 463-464.

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Naproxen and Its Phototransformation Products: Persistence and Ecotoxicity to Toad Tadpoles (Anaxyrus terrestris), Individually and in Mixtures
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Forrest, M., G. Rouse, J. Stiller, T. King. 2017. Between Hot Rocks and Dry Places: The Status of the Dixie Valley Toad. Western North American Naturalist , 77(2): 162–175.

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Green, D., K. Yagi. 2018. Ready for bed: pre-hibernation movements and habitat use by Fowler’s Toads (Anaxyrus fowleri). Canadian Field-Naturalist , 132(1): 46–52. Accessed February 02, 2020 at https://doi-org.ezproxy2.library.colostate.edu/http://dx.doi.org/10.22621/cfn.v132i1.2023 .

Mucignat-Caretta, C. 2014. Neurobiology of Chemical Communication . Boca Raton, FL, USA: CRC Press/Taylor & Francis. Accessed December 18, 2023 at https://www.ncbi.nlm.nih.gov/books/NBK201000/ .

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Peralta-Garc, A., D. Leavitt, B. Hollingsworth, T. Reeder. 2016. The Phylogenetic Position of the Little Mexican Toad, Anaxyrus kelloggi, Using Molecular Data. Journal of Herpetology , 50(3): 471–475. Accessed February 02, 2020 at https://doi-org.ezproxy2.library.colostate.edu/http://dx.doi.org/10.1670%2F15-105 .

Pitt, A., J. Tavano, R. Baldwin, T. Waldrop. 2013. Effects of fuel reduction treatments on movement and habitat use of American toads in a southern Appalachian hardwood forest. Forest Ecology and Management. Elsevier B.V , 310: 289–299. Accessed February 02, 2020 at https://doi-org.ezproxy2.library.colostate.edu/https://dx.doi.org/10.1016/j.foreco.2013.08.032 .

Rumrill, C., D. Scott, S. Lance. 2018.

Delayed effects and complex life cycles: How the larval aquatic environment influences terrestrial performance and survival
. Environmental Toxicology and Chemistry , 37(10): 2660–2669. Accessed February 02, 2020 at https://doi-org.ezproxy2.library.colostate.edu/http://dx.doi.org/10.1002/etc.4228 .

Sullivan, B., J. Wooten, T. Schwaner, K. Sullivan, M. Takahashi. 2015.

Thirty Years of Hybridization between Toads along the Agua Fria River in Arizona: I. Evidence from Morphology and mtDNA
. Journal of Herpetology , 49(1): 150-156. Accessed February 02, 2020 at https://doi-org.ezproxy2.library.colostate.edu/http://dx.doi.org/10.1670%2F14-011 .

Thompson, P. 2019. Translocation of Boreal Toad (Anaxyrus boreas boreas) into Two Springs in the Grouse Creek Mountains, Utah, Including Demographic Observations. Western North American Naturalist , 79(1): 24–36.

2020. "Anaxyrus americanus (Holbrook, 1836) --American Toad" (On-line). Illinois Natural History Survey. Accessed March 24, 2020 at https://www.inhs.illinois.edu/index.php?cID=1011 .

1998. "Taxonomy Chapter for Toad, eastern American" (On-line). Virginia Fish and Wildlife Information Service. Accessed March 24, 2020 at https://vafwis.dgif.virginia.gov/fwis/booklet.html?&bova=020059&Menu=_.Taxonomy&version=17612 .

To cite this page: Kinder, K. 2025. "Anaxyrus" (On-line), Animal Diversity Web. Accessed {%B %d, %Y} at https://animaldiversity.org/accounts/Anaxyrus/

Last updated: 2025-27-30 / Generated: 2025-10-03 00:52

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