Frogs and Toads of the United States

There are nine families of frogs and toads found in the United States, the remainder are found in South America, Europe, Africa,, Asia, Australia, and the South Pacific Islands. A total of 81 species occur north of Mexico.

Most species return to the water to breed. Eggs are laid in the water and are fertilized by the male while clasping the female. The eggs hatch into tadpoles which later transform into young frogs and toads. A number of frogs and toads lay their eggs in shaded moist sites on land, or in nests constructed over water. The eggs may hatch into tadpoles that either drop into the water, are swept into the water by rains, or are carried to the water by a parent. Other species bypass the tadpole stage, their eggs hatching directly into miniature frogs. Finally, the African live bearing toad, Nectopgrynoides, and the North American Tailed Frog, Ascaphus, are unique among fromgs and toads in the they fertilize the eggs within the cloaca of the female.

 

Ascaphidae (Tailed Frogs)

One species on the Northwestern United States and southwestern Canada. These are primative frogs with 2 pairs of unattached ribs and 9 presacral vertebrae. The pupil is vertical. None of the species has a true tail, but all possess tail wagging muscles. Male Ascaphus have a unique tail like extension of the vent that servers as a copulatory organ for passing sperm directly into the body of the female, while clasping her around the waist.

All tailed frogs live in cool mountain habitats, but reproduction varies. Leiopelma lays its eggs on damp earth where they hatch 6 weeks later as miniature frogs. Ascaphus lays its eggs in cold mountain streams where they hatch into tadpoles, transforming into frogs more than 6 months later.

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Rhinophrynidae (Burrowing Toads)

Only 1 species, Rhinophrynus dorsalis, found from Coast Rica to Texas. This frog lacks a breastbone. The pupil is vertical. In addition, its tongue is attached in the back of the mouth and free in the front, unlike the typical toad or frog, so that it protrudes like the tongue of most vertebrates. Rhinophrynus is adept at burrowing, making use of the spade on each hind foot to shuffle backward into the soil. Breeding males clasp the females around the waist. Eggs are laid in the water.

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Ranidae (True frogs)

True frogs have a bony breastbone and horizontal pupils. North American species have large frogs with slim waists, long legs, pointed toes, and extensive webbing on the hind feet. They are excellent jumpers. The adults are truly amphibious, typically living along the edge of water and entering it daily to catch prey, flee danger, or to mate. They are all voracious cornivores, feeding primarily on insects, spiders, and crustaceans, but readily accepting anything else that can be caught and swallowed.

Mating usually is initiated in the springs with aggregations of males calling in chorus to attract females to the breeding site. The breeding male has swollen forearms and thumbs for clasping the female behind her forelegs. In the water, female Rana may lay strings or rafts containing up to 20,000 eggs. Eggs hatch within a month, with tadpoles metamorphosing into frogs 6 to 24 months later.

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Microhylidae (Narrow-Mouthed Frogs)

Only 2 genra with 3 species total are found in the United States, there are Gastrophryne and Hypopachus. Narrow-mouhted frogs have a reduced shoulder girdle. The North American species lack teeth, and have a fold of skin across the back of the narrow, pointed head. They body is plump and the skin smooth and moist. The legs are short and the hind feet have enlarged tubercles used in digging. They are scretive creatures active only at night and feed almost excusively on ants.

Males give a bleating call to attract feamles to the breeding ponds. In addition to being clasped firmly behind the forelimbs by the male, the female narrow-mouthed frogs sticky skin scretion also holds the breeding pair together. The eggs are laid in a thin, floating film and hatch a few days later. Tadpoles metamorphose in about 30 days.

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Bufonidae (Toads)

(REVISED 2006): Only one genus with 3 species occur in our range

Toads are squat and plump with rough warty skin. They have horizontal pupils, no teeth on the upper jaw, and lack the acnterior breastbone. Enlarged parotoid glands are located on each side of the neck over or behind the tympanum. These glands secrete a viscous white poison, which gets smeared in the mouth of any would be predator. The poison inflames the mouth and throat, causing nausea, irregular heartbeat, and, in extreme cases, death. Survivors of such a poisoning seldom ever again attack toads.

Toads in our range breed in spring and summer. Males congregate at the breeding ponds and sing in order to attract females. Males clasp the willing females around the body behind the forelimbs. Males also have rudimentary ovary, which can become functional ir the testes are damaged of removed. Eggs are usually laid in strings attached to vegetation. They hatch into tiny black tadpoles which weeks later metomorphose into lieel toads.

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Hylidae (Treefrogs)

There are 7 genera with 26 species in North America. Treefrogs are small and have slender legs and their pupils are horizontal.

Arboreal treefrogs are typically walkers and climbers, and are reluctant jumpers. Their toe tips are expanded into sticky adhesive pads used in climbing. Limbing is further aided by the presence of cartilage between the last two bones of each toe. The cartilage allows the tips of the toe to swivel backward and sideways while keeping the sticky toe pad flat against the climbing surface. A few treefrogs, such as the North American Acris, have returned to a terrestrial existence, lack the large toe pads, and are active leapers.

Male treefrogs in our range typically call while perched on vegetation in, over or near water. Males clasp females just behind the forelimbs. Masses of eggs are laid in the water.

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Leptodactylidae (Leptodactylid Frogs)

The 7 species that occur on North America have horizintal pulils, and a T shaped bone in the tip of each toe.

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Pipidae (Tongueless Frogs)

One species, Xenopus laevis, has been introducted in North America.

Tongueless frogs have attached ribs and eight presacral vertebrae. Their pupils are round. The South American species have starlike projections on the tips of the toes of the front feet while the African species have simple pointed toes on the front feet. The latter attach their eggs singly to submerged vegetation, logs, or stones. Thousands of eggs are laid at a time. During breeding, the male clasps the female around the waist.

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