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Anaxyrus debilisGreen Toad

By Sydni Smith

Geographic Range

Green toads (Anaxyrus debilis) are located in the Nearctic region, specifically, the southwestern United States. The largest populations of green toads are found in northern Mexico. In Mexico, they range from the Mexico-Texas border southward to Zacatecas and San Luis Potosi, Mexico. They also exist just south of the Arizona border. In the United States, green toads range from central Texas northwards towards southwestern Oklahoma and western Kansas. They can also be found in southeastern Colorado and southeastern Arizona. Green toads do not migrate. (Altig and McDiarmid, 2015; Hammerson and Santos-Barrera, 2004; Lanoo, 2005; Powell, et al., 2016)

Habitat

Green toads are desert-dwelling toads whose habitats include the northern Chihuahuan desert. This desert includes shrubs, semi-desert, and shrub steppe habitats. Many of these areas are unvegetated. Green toads burrow in mesquite (Prosopis) shrubs, which provide shelter and a means to regulate the toads body temperature.

During the dry season, green toads can be found under rocks. After rainfall, green toads will breed in temporary water sources such as roadside ditches and vernal pools. Seymour (1972) found that juvenile toads will bask on mud banks in an attempt to increase their internal body temperature to as high as 30 °C. Toadlets will also seek refuge in fissures in the mud.

Elevational limits or ranges have not been reported. However, those populations at higher, cooler elevations use burrows for a longer amount of time than those at lower elevations. (Boeing, et al., 2014; Goldberg, 2019; Lanoo, 2005; Seymour, 1972; Taggart and Rieldle, 2017)

  • Aquatic Biomes
  • temporary pools

Physical Description

Adult green toads, like their name suggests, are green with a mix of yellow. Both male and females have black spots. Often, these black spots fuse together to form black striations on their bodies. The ventral side of both sexes is white and lacks spots. Male green toads have black throats, while females’ throats are white or yellow. Both sexes have flat, wedge shaped heads.

Male green toads are smaller than females. Torres-Cervantes et al. (2019) reported lengths and weights for green toads in the Chihuahuan Desert. Males’ average size was 36.6 mm snout-vent length (SVL) (range 31.5 - 45.3 mm) and females average 43.2 mm SVL (range 41.8–44.0 mm). Female green toads' body mass averaged 10.0 g (range 9.2 - 10.7 g). Male mass averaged 6.0 (range 3.0 – 9.5 g). In other studies, adult females reached 54 mm SVL, while adult males were as small as 26 mm post-metamorphosis.

Green toads can release toxins through their parotoid glands in their skin. The toxin is cardiotoxic steroids, which is undesirable to predators.

Green toad tadpoles have rounded bodies. Their anal tube opening is located on the right side of their tail fins. Their eyes are located dorsally and the tail fins are not fully developed. Their abdomens are black with gold flecks. Tadpoles are otherwise transparent. They hatch at lengths between 3.1 to 3.4 mm. (Goldberg, 2019; Lanoo, 2005; Taggart and Rieldle, 2017; Torres-Cervantes, et al., 2019)

  • Sexual Dimorphism
  • female larger
  • sexes colored or patterned differently
  • Range mass
    3 to 10.7 g
    0.11 to 0.38 oz
  • Range length
    26 to 54 mm
    1.02 to 2.13 in

Development

Green toads exhibit indeterminate growth. Like all toads, they go through metamorphosis from tadpole to adult. Green toads lay their eggs in small strings. The eggs attach to herbaceous stems, including grass. The ova size from two samples was 0.98 mm and 1.15 mm. Embryos found in southwest Arizona hatched within 24 hours with water temperatures at 33.2 °C. When water temperature was at 18.2 °C, the time required for hatching was 140 hours. Green toads’ average length at hatching is 3.1 to 3.4 mm.

There is a wide range of developmental dates. Metamorphosis typically takes less than 3 weeks. However, in Kansas, the tadpole stage exceeded 25 days. Taggart (1997) found development from zygote to juvenile lasted only 8 days.

Green toad larval development is dependent on environmental factors, like the amount of rainfall and temperature. Metamorphosis ends around froglet lengths of 19-20 SVL. Males are sexually mature at lengths of 26-41 mm SVL, while females are mature at 31-46 mm SVL. Males in southwest Mexico have been reported to begin calling at 37 mm SVL. In the same study, female green toads in amplexus ranged between 44-54 mm SVL. (Boeing, et al., 2014; Goldberg, 2019; Lanoo, 2005)

Reproduction

Green toads mate seasonally from late March to July, immediately after heavy rainfall. They mate in vernal pools. During this time, males attract females through their calls in chorus. Mating occurs via amplexus and reproduction occurs externally when eggs are released in tandem. Reproductively-active males are 26 to 41 mm SVL. Male green toads join choruses around 37 mm SVL. In southwest New Mexico, females in amplexus were 44 to 54 mm SVL. Green toads have many mating partners during mating season and are polygynandrous. (Boeing, et al., 2014; Goldberg, 2019; Lanoo, 2005)

Green toads are iteroparous, leaving their burrows after heavy rainfall to mate. Some green toads will travel several kilometers to different breeding sites with water. Green toads will migrate to multiple bodies of water during one season. Male green toads join in chorus to attract females. Female green toads will locate males to mate. These anurans exhibit rapid short-term breeding events just after heavy rainfall. Their breeding often lasts one night. Reproductively-active males are 26 to 41 mm SVL. In southwest New Mexico, females in amplexus were 44 to 54 mm SVL. During amplexus, female green toads lay, on average, 1,287 eggs. Green toad eggs are laid in small strings. The eggs attach to herbaceous stems, including grass. Egg size ranges from 0.98 mm to 1.15 mm.

Embryos found in southwest Arizona hatched within 24 hours with water temperatures at 33.2 °C. When water temperature was at 18.2 °C, the time required for hatching was 140 hours. Tadpoles are immediately independent at hatching.

Males are sexually mature at lengths of 26-41 mm SVL, while females are mature at 31-46 mm SVL. No ages have been associated with these lengths. (Boeing, et al., 2014; Goldberg, 2019; Lanoo, 2005)

  • Breeding interval
    After heavy rainfall from late March to July, for one night
  • Breeding season
    March through July
  • Average number of offspring
    1287
  • Range time to hatching
    24 to 140 hours
  • Average time to independence
    0 minutes

Parental investment for green toads is limited to the act of mating. They leave egg masses attached to herbaceous stems in water, and then provide no further care. At hatching, the tadpoles are independent. (Lanoo, 2005)

  • Parental Investment
  • no parental involvement

Lifespan/Longevity

The longevity of green toads is unknown. Most green toads will not survive to adult size in the wild. In captivity, the longest life span reported was 12.4 years. American toads (Anaxyrus americanus) have a maximum lifespan of 10 years in the wild. Green toads likely have similar life spans in the wild. (Lanoo, 2005; Slavens and Slavens, 2018; Smirina, 1994)

  • Range lifespan
    Status: captivity
    12.4 (high) years
  • Typical lifespan
    Status: wild
    10 (high) years

Behavior

Male green toads join in chorus to attract female green toads. There is no correlation between toad size, temperature, and variation in calls. Male green toads do not use active search methods to locate females. They mate from late March until July during nocturnal hours. Breeding occurs in aquatic locations. They only come out of burrows for mating and mate via amplexus (external fertilization).

Green toads are inactive unless it is humid or after heavy rainfalls. From September to May, green toads typically remain inactive (hibernating) and below ground. Green toads do not swim great distances, only using temporary pools to breed. They do hop on terrestrial ground. They do not migrate seasonally, but they sometimes travel several kilometers to reach breeding pools. Here they join large choruses of frogs.

During the dry season, they are solitary, finding shelter under rocks. They use sunlight to thermoregulate and absorb water while basking. To absorb water, they place their anterior side into the soil. (Boeing, et al., 2014; Lanoo, 2005; Seymour, 1972; Sullivan, 1984)

Home Range

Home range size for green toads is unknown. During breeding, calling males can be found 0.5 to 0.3 m apart from each other. Occasionally, and they can be as close as 0.1 m from each other. They are not known to actively defend an area. (Lanoo, 2005)

Communication and Perception

Green toads communicate through calls in chorus. Males’ advertisement calls are described to be similar to crickets, as long high-pitched trills. They typically last less than 7 seconds. The breeding choruses begin after rainfall and last 1 to 3 days. The female locates the male via choruses (acoustics) to mate. Male toads do not search for females.

Vision is utilized in mate recognition, as males and females can be differentiated by throat color. Males have black colored throats and females have white or yellow. When mating, they use tactile efforts, as males grasp females in amplexus.

When threatened, green toads release indolealkylamines from their skin, including paratoid glands. The chemicals are distasteful to predators. (Lanoo, 2005; Luria-Manzano and Ramirez-Bautista, 2019; Sullivan, 1984; Taggart and Rieldle, 2017)

Food Habits

Green toad tadpoles feed on algae found in the substrate of ephemeral pools. They also feed on detritus and periphyton. Luria-Manzano and Ramirez-Bautista (2019) reported diets of 10 green frogs in the Chihuahuan Desert. Their diets included beetles (Order Coleoptera, 12% of volume), ants (Order Hymenoptera, 31%), termites (Isoptera, 56%), caterpillars (Order Lepidoptera, 0.5%), and earwigs (Dermaptera, 0.02%). Plant matter was also found in stomach contents. They may also eat a variety of insects, like grasshoppers and crickets (Order Orthoptera). (Lanoo, 2005; Luria-Manzano and Ramirez-Bautista, 2019)

  • Animal Foods
  • insects
  • terrestrial non-insect arthropods
  • Plant Foods
  • wood, bark, or stems
  • algae

Predation

Green toad tadpoles are more likely to be preyed upon than adults. Known predators of tadpoles and adults are black-necked garter snakes (Thamnophis cyrtopsis). Eggs and tadpoles are known to be attacked by dragonfly larvae (Order Odonata). Because adult green toads are fossorial and terrestrial, many of the predators include snakes. Some of the snakes include gopher snakes (Pituophis catenifer), checkered garter snakes (Thamnophis marcianus), plains garter snakes (Thamnophis radix), and western hog-nosed snakes (Heterodon nasicus). Green toads are also attacked by invertebrates including giant water bugs (family Belostomatidae) and water scavenger beetles (family Hydrophilidae). American bullfrogs (Lithobates catesbeianus) also prey on these toads.

Green toad adults avoid predation by remaining underground for much of the year. If they become threatened during choruses, green toads will retreat underwater or hide in vegetation. Green toads can release toxins (cardiotoxic steroids) through their parotoid glands. (Lanoo, 2005)

Ecosystem Roles

Known predators of green toads are snakes, and predaceous aquatic insects. Green toads likely feed opportunistically on a variety of invertebrates.

Parasites of green toads in New Mexico include tapeworms (Distoichometra bufonis) and roundworms or nematodes (Rhabdias americanus, Aplecctana incerta, Alpecctana itzocanenis, and Physaloptera pirurida). In central Texas, these toads were affected by endoparasites including ciliates (Nyctotherus cordiformis), and cnidarian myxizoans (Myxidium serotinum). Green toads’ blood samples were negative for endoparasites like apicomplexans and trypanosomes. Unidentified protozoans in the SAR clade, family Opalinidae, also were found in Texas. (Lanoo, 2005)

Commensal/Parasitic Species
  • cestodes (Distoichometra bufonis)
  • cnidarian parasites (Myxidium serotinum)
  • ciliates (Nyctotherus cordiformis)
  • nematode (Rhabdias americanus)
  • nematode (Alpeccatana incerta)
  • nematode (Alpeccatana itzocanenis)
  • nematode (Physaloptera pirurida)
  • protozoans in the SAR clade (family Opalinidae)

Economic Importance for Humans: Positive

Green toads have occurred in amphibian trade in Texas. Many of them were exported to other countries by online sources. Anurans export and import is on the rise in Texas. (Prestridge, 2009)

Economic Importance for Humans: Negative

There are no known adverse economic effects of green toads on humans.

Conservation Status

Green toads do not have special status on the US federal list, CITES, and the State of Michigan List. They are listed as a species of "Least Concern" on the IUCN Red List. Green toads are protected by Kansas. They are also protected by Mexican law.

The historical abundance of green toads is not known, but they are often found in locations with suitable habitat. Their localized populations have likely declined, due to habitat loss, including temporary wetlands. Changes in land-use have led to many green toad habitats becoming unsuitable.

There have been attempts in Kansas to reintroduce green toads into historical areas. However, no attempts have been successful. There is not a recovery plan for green toads. (Hammerson and Santos-Barrera, 2004; Lanoo, 2005; Taggart, 2021)

Contributors

Sydni Smith (author), Radford University, Karen Powers (editor), Radford University, Victoria Raulerson (editor), Radford University, Christopher Wozniak (editor), Radford University, Genevieve Barnett (editor), Colorado State University.

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

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

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.

herbivore

An animal that eats mainly plants or parts of plants.

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.

indeterminate growth

Animals with indeterminate growth continue to grow throughout their lives.

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.

pet trade

the business of buying and selling animals for people to keep in their homes as pets.

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.

saltatorial

specialized for leaping or bounding locomotion; jumps or hops.

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

social

associates with others of its species; forms social groups.

solitary

lives alone

tactile

uses touch to communicate

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

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