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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) Biogeographic Regions nearctic native 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) Habitat Regions temperate terrestrial freshwater Terrestrial Biomes chaparral forest rainforest scrub forest mountains Aquatic Biomes lakes and ponds rivers and streams Wetlands marsh swamp bog Other Habitat Features urban suburban agricultural riparian 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) Other Physical Features ectothermic heterothermic bilateral symmetry poisonous 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) Development - Life Cycle metamorphosis 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). Mating System polygynous polygynandrous (promiscuous) 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.
On a hiking trail in the woods.
Spotted on May 1, 2011
Submitted on May 1, 2011