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Anaxyrus americanusAmerican Toad

By Stacey Grossman

Geographic Range

American toads, Anaxyrus americanus, are only native to the Nearctic region. They are found throughout large portions of North America, from northern Chihuahua in Mexico, northward to James Bay in Canada and eastward from the Imperial Valley of California and the Columbia River Valley in Washington and Oregon to the Atlantic coast from Florida to southern Quebec. They are generally not present in the most southern states or, if they are, only in the northern part. These toads have an immense ability to adapt to their surroundings as long as there is a source of semi-permanent water for them to use in the breeding season. This quality has allowed them to successfully colonize suburban and agricultural areas. (Dickerson, 1906; Oliver, 1955)

Habitat

American toads require a semi-permanent freshwater pond or pool for their early development. They also require dense patches of vegetation, for cover and hunting grounds. Given these two things and a supply of insects for food, American toads can live almost everywhere, ranging from forests to backyards. They are common in gardens and agricultural fields. During daylight hours they seek cover beneath porches, under boardwalks, flat stones, boards, logs, wood piles, or other cover. When cold weather comes, these toads dig backwards into their summer homes or may choose another site in which to hibernate. (Le Clere, 2000; Lerner, June 13 1998; Matson, 2002; Rakestraw, 1998)

  • Aquatic Biomes
  • lakes and ponds
  • rivers and streams

Physical Description

American toads have short legs, stout bodies, and thick skins with noticeable warts. These warts can be colored red and yellow. The warty skin contains many glands that produce a poisonous milky fluid, providing these toads with excellent protection from many of their predators. This poison is only harmful if it is swallowed or if it gets in the eyes, but it can make many animals very sick. (Dickerson, 1906; Le Clere, 2000; Matson, 2002; Oliver, 1955)

The skin color of American toads is normally a shade of brown, but it can also be red with light patches, olive, or gray. The bellies are a white or yellow color. Toad skin color changes depending on temperature, humidity, and stress. The color change ranges from yellow to brown to black. American toads have four toes on each front leg and five toes connected together by a webbing on each hind leg. The pupils of American toads are oval and black with a circle of gold around them. The sexes can be distinguished in two ways. Males have dark colored throats, of black or brown, while females have white throats and are lighter overall. Also, female American toads are larger than male American toads. American toads are between 50 and 100 mm in length but are usually around 75 mm. American toads can be distinguished from other species of toads by the presence of several dark spots on their backs which contain only one or two warts each. These black spots are sometimes circled with white or yellow. Some types of American toads have a prominent ridge on the top of their heads. (Dickerson, 1906; Le Clere, 2000; Matson, 2002; Oliver, 1955)

The eggs of American toads are black on top and white on the bottom (countershaded), and embedded in long strings of clear sticky gel. The larvae that hatch from eggs are called "tadpoles." They are dark (almost black) with smooth skin, round bodies, and a somewhat rounded tail. Like adult toads, larvae have defensive chemicals in their skin. They grow to over a centimeter in length before transforming. Newly-metamorphosed toadlets are usually 0.8 and 1.3 cm long when they first emerge. Their coloration is similar to that of adult toads. (Dickerson, 1906; Le Clere, 2000; Matson, 2002; Oliver, 1955)

  • Sexual Dimorphism
  • female larger
  • sexes colored or patterned differently
  • Range length
    50 to 102 mm
    1.97 to 4.02 in
  • Average length
    75 mm
    2.95 in

Development

Female American toads lay their eggs in freshwater. Hatching occurs 3 to 12 days after laying, depending on the temperature of the water. The tadpoles group together and feed and grow for 40 to 70 days.

When the tadpoles hatch they have gills located on the sides of their heads just posterior to their mouths. During the first 20 days the tadpoles start to form their hind legs. The legs grow slowly, but continuously. After 30 to 40 days the front legs, which were previously covered by a layer of skin, appear. At the same time that the front legs emerge, the tadpoles' gills disappear, and the tadpoles start to breathe "atmospheric" air. Between the last two or three days of development, they complete their metamorphosis, resorbing their tails and strengthening their legs. They also stop eating plants in favor of animal matter.

Newly-metamorphosed toads stay near their pond for a few days (or longer if the climate is dry), and then disperse and begin to live primarily on land. American toads continue to grow until they reach their full adult size of approximately 75 mm.

American toads, while still growing, shed their external skin every couple of weeks or so. Older frogs lose their skin around four times yearly. The skin peels off in one piece, and is collected under its tongue, where it is then gulped down. (Dickerson, 1906; Matson, 2002; Oliver, 1955)

Reproduction

Breeding occurs in the months of March or April, but may extend into July. It usually triggered by warming temperatures and longer days. The males always arrive on the mating grounds well ahead of females. They congregate in shallow wetlands, ponds, lakes and slow-moving streams. After finding a suitable area, the male toads establish territories and begin calling the females. Females may choose their mates by assessing the males' breeding calls as well as the quality of the defended breeding territory.

Male toads get dark horny pads on their first and second two toes on their forelegs. This helps them close their front limbs around a female's abdomen in a posture called "amplexus". Once a female comes close, any nearby male will attempt to mate with her. The male holds on to the female, and she moves to a suitable location in the water to lay eggs. When she releases her eggs, he releases sperm to fertilize them (like most frogs and toads, fertilization is external).

After mating takes place, the females lay their eggs in the water, in long spiral tubes of jelly. They lay 4000 to 8000 eggs in two rows. When each row of eggs is stretched it generally measures between between six and twenty meters long (20 to 66 ft.). Each individual egg is 1.5 mm in diameter. The eggs mature fastest at higher temperatures. They generally hatch in 3 to 12 days. After developing for 40 to 70 days, the tadpoles transform into adults. This usually takes place from June to August, depending on location. They reach sexual maturity at around 2 to 3 years of age.

  • Breeding interval
    American toads breed from once yearly.
  • Breeding season
    American toads breed from March to July each year, depending on location.
  • Range number of offspring
    4000 to 8000
  • Range time to hatching
    2 to 14 days
  • Range age at sexual or reproductive maturity (female)
    2 to 3 years
  • Range age at sexual or reproductive maturity (male)
    2 to 3 years

Female toads provide nutrients for their eggs inside their bodies. Once the eggs are laid and fertilized, the parents ignore them.

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

Lifespan/Longevity

In the wild most American toads probably don't survive more than a year or two. The majority die before transforming from tadpoles into toadlets. However, they are capable of living much longer. Some toads have lived longer than 10 years in the wild. There is a documented account of a captive toad that lived to the ripe old age of 36 and was killed by mistake. (Dickerson, 1906; Harding, 1997; Oliver, 1955)

  • Range lifespan
    Status: wild
    0 to 10 years
  • Average lifespan
    Status: wild
    < 1 years
  • Range lifespan
    Status: captivity
    0 to 36 years

Behavior

American toads are mainly nocturnal. They are most active when the weather is warm and humid. They are solitary, congregating only at breeding ponds in the early summer and late spring. During the day American toads hide under rocks or logs or dig into dead leaves and soil. In regions with a cold winter, American toads dig deeper to hibernate. When digging they back in, pushing out dirt with their back legs.

(Harding 1997, Mullin, 1998; Dickerson, 1906) (Dickerson, 1906; Harding, 1997)

Communication and Perception

American toads have one of the most notable calls of all toads. They give off long trill sounds that each last between 4 and 20 seconds. American toads use this call as a way to attract females for breeding. Their calls become frantic, loud, and constant during mating season. Many young males continue to call late into the summer. When they call, their throats puff out like large, inflatable balloons.

American toads also use body postures, touch, and chemical cues for communicating.

Food Habits

Adult American toads are carnivores, but toad tadpoles are considered herbivores, because they graze on aquatic vegetation (algae).

Adult American toads are generalists. They eat a wide variety of insects and other invertebrates, including snails, beetles, slugs, and earthworms. Unlike most toads, who wait for prey to come along and pounce on it, American toads can shoot out their sticky tongues to catch prey. They also may use their front legs in order to eat larger food. They grasp their food and push it into their mouths. One American toad can eat up to 1,000 insects every day.

Toads do not drink water but soak it in, absorbing moisture through their skin. (Harding, 1997; Le Clere, 2000; Lerner, June 13 1998)

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

Predation

The main predators of American toads are snakes. One species, eastern hognose snakes, specializes on eating toads. Some snakes, such as garter snakes, are immune to the poisonous glands of American toads. When these toads are faced with a predator that is immune to their poison they will sometimes urinate on themselves to become a less attractive meal. They also inflate their bodies with air to make themselves more difficult for a snake to swallow.

Female toads prefer to lay their eggs in ponds without fish. The eggs they lay are countershaded: lighter on the bottom and darker on the top to blend in with the background when viewed from above or below.

Tadpoles avoid predators by swimming in very shallow water, and by swimming close together in schools during the day. They also have toxic chemicals in their skin that discourage some potential predators. Metamorphosed toads are cryptically colored, and are actively mainly at night, making it harder for predators to find them. (Dickerson, 1906; Harding, 1997; Le Clere, 2000)

  • Anti-predator Adaptations
  • cryptic

Ecosystem Roles

American toads are responsible for controlling the populations of many kinds of insects. The number of insects they eat makes them a crucial part of controlling these populations. (Dickerson, 1906)

Economic Importance for Humans: Positive

American toads eat many species of pest insects and other invertebrates. They are widely considered friends to gardeners and farmers. The toxins produced by their skin may eventually prove useful in medical research. (Dickerson, 1906)

  • Positive Impacts
  • research and education
  • controls pest population

Economic Importance for Humans: Negative

There are no negative impacts of American toads on humans.

Conservation Status

American toads have no special conservation status, as they are still common in most of their range. Some populations have declined in recent years, possibly due to pollution.

Other Comments

American toads are the most widespread toad species in North America.

There are two subspecies of American toads, eastern and dwarf. Dwarf American toads live mainly in the west, eastern American toads live in the eastern portions of the range.

Contrary to folk-belief, you will not get warts if you touch a toad. However, the defensive chemicals in toad skin are toxic to humans, so its important to wash one's hands carefully after handling one.

Contributors

Allison Poor (editor), University of Michigan-Ann Arbor.

Stacey Grossman (author), Fresno City College, Carl Johansson (editor), Fresno City College.

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.

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.

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

choruses

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

crepuscular

active at dawn and dusk

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.

diurnal
  1. active during the day, 2. lasting for one day.
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

forest

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

freshwater

mainly lives in water that is not salty.

herbivore

An animal that eats mainly plants or parts of plants.

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.

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.

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).

marsh

marshes are wetland areas often dominated by grasses and reeds.

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.

mountains

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

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).

polygynandrous

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

polygynous

having more than one female as a mate at one time

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.

riparian

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

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

solitary

lives alone

suburban

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

swamp

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

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.

urban

living in cities and large towns, landscapes dominated by human structures and activity.

visual

uses sight to communicate

References

1999. "Ohio History Center" (On-line). Accessed Sept. 20,2001 at http://www.ohiohistorycentral.org/ohc/nature/animals/reptile/americantoad.shtml.

Dickerson, M. 1906. The Frog. NY: Doubleday, Page and Company.

Harding, J. 1997. Amphibians and Reptiles of the Great Lakes Region. Ann Arbor, Michigan, USA: The University of Michigan Press.

King, R., M. Oldham, W. Weller, D. Wynn. 1997. Historic and current amphibian and reptile distributions in the island region of western Lake Erie. American Midland Naturalist, 138 (1): 153-173.

Le Clere, J. 2000. "American Toad" (On-line). Accessed Sept. 20,2001 at http://herpnet.net/Iowa-Herpetology/amphibians/frogs_toads/american_toad.html.

Lerner, J. June 13 1998. Growing a Garden of Wildly Delights. The Washington Post: G 16.

Matson, T. 2002. "An Introduction to the Natural History of the Frogs and Toads of Ohio" (On-line). Accessed Sept. 20,2001 at http://www.cmnh.org/collections/vertzoo/frogs/americanus.html.

Milius, S. 1998. Fatal skin fungus found in U.S. frogs. Science News, 154(1): 7.

Oliver, J. 1955. The National History of North American Amphibians and Reptiles. Princeton: D. Van Nostrand Company. Inc..

Rakestraw, J. 1998. Turning Over Rocks. Country Journal, 25 (3): 52-56.

Withgott, J. 2001. Feeling The Burn. Natural History, 110(6): 38-45.

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