Bullfrog

American Bullfrog
Bullfrog, Lithobates catesbeianus
Conservation status
Least Concern
Scientific classification
Kingdom: Animalia Phylum: Chordata Class: Amphibia Order: Anura Family: Ranidae Genus: Lithobates Species: L. catesbeianus
Binomial name
Lithobates catesbeianus (Shaw, 1802)
Bullfrog range
Synonyms
Rana catesbeiana

Bullfrog is the common name of the largest North American frog, Lithobates catesbeianus or Rana catesbeiana, a semi-aquatic, heavy-bodied frog native to eastern North America, from Mexico to southern Canada, but introduced into western North America and other countries. While traditionally classified as Rana catesbeiana, recent taxonomies place it in the Lithobates genus (Frost 2006a; Frost 2006b). It is in the Ranidae family ("true frogs") of the order Anura . Other large frogs in other species are sometimes called bullfrog and Lithobates catesbeiana is sometimes distinguished as the American Bullfrog.

Distribution and habitat

Bullfrog in typical aquatic habitat.

While native to eastern North America, from Mexico to Canada, the species has been introduced successfully into western North America, Central and South America, islands in the Caribbean, China, Japan, Thailand, various European countries, and several oceanic islands (Grzimek et al. 2004). In Europe and the western U.S., measures are often taken to control its spread because it competes with, and often drives out, native species.

Although found in many habitats, the bullfrog particularly favors larger bodies of water relative to other frogs (Grzimek et al. 2004). Bullfrogs dig into the mud to hibernate in cold winter weather.

Physical description

The bullfrog is a large species of the Ranidae family and the largest frog in North America, reaching a length of 8 inches (203 millimeters) and a weight of up to 3.3 pounds (1.5 kilograms) (Grzimek et al. 2004). Females are typically larger than males.

Bullfrogs are generally varying shades of green, olive, or brown, with dark brown, dark green, or black blotching and a yellow or white underside.

The skeleton of an adult frog consists of bone, hyaline cartilage, and calcified cartilage. The calcified cartilage can be found throughout the body of the frog, but it is particularly more noticeable in the epiphyses of the long bones in the limbs and shoulder-gridle. The radius and ulna are fused into a single bone, the radio-ulna, and the tibia and fibula are fused into a single bone, the tibio-fibula. The vertebrae comprise ten bones; nine are true vertebrae, and the rod-shaped urostyle that is almost as long as the other nine.

A young female with a relatively small tympanic membrane

The head of the frog is flat but its form depends on the extensive separation of the jaw bones; the orbital cavities and the horizontal direction of their floor also have an effect on the form of the head. The central nervous system is made up of the spinal cord and the brain, where the spinal cord is a bit smaller than the brain. The peripheral nervous system contains the cranial nerves and spinal nerves.

They have four legs, not two hands and two legs as commonly misconceived. Front feet and back feet are both webbed. the hind limbs are long. The bull frog has large talons.

The bullfrog uses its skin, buccal cavity, and lungs for respiration. Cutaneous ("skin") gas exchange is very important in all amphibians.

The tympanum is relatively large, particularly in males (Grzimek et al. 2004). Males also have nuptial pads, yellowish throats, and single internal vocal sacs.

Behavior, feeding, life cycle, and reproduction

Bullfrog, R. catesbeiana

The life cycle of bullfrogs, like that of other frogs, consists of the main stages of egg, tadpole, metamorphosis, and adult.

Bullfrogs are aptly named since their call is a loud, guttural bellow that carries a long distance, giving the impression that the frog is much larger than it actually is, which is an advantage in keeping predators away.

The male reproductive organs are the testes and their duct, and the female have ovaries. In the spring the male calls the female from the water. The female lays up to 25,000 eggs, and these eggs become tadpoles. Their metamorphosis brings them the organs that are only found in the adult frogs and takes between 12-24 months. There are three major changes that take place during the metamorphosis:

1. Premetamorphisis which is when the embryo genesis and growth and development occur, during this time the thyroid gland is absent.
2. Prometamorphisis is the period in which the concentration of the endogenous thyroid hormone rises.
3. Metamorphosis is the period when the tadpole's tail shrinks back into the frog's body. Other organs also undergo changes such as the liver and the intestine. The gills are absorbed as well.

The adult frog can live up to 13 years.

Bullfrog tadpole

Human use

While occasionally kept as pets, the American Bullfrog provides a minor food source, especially in the Southern United States and in some areas of the Midwestern United States. In a few locations they are commercially cultured in ponds, but the traditional way of hunting them is to paddle or pole silently by canoe or flatboat in streams or swamps at night; when the frog call is heard, a light is shined on the frog to temporarily inhibit it. The frog will not jump into deeper water as long as movement is slow and steady. When close enough, the frog is gigged and brought into the boat. The only parts eaten are the rear legs, which resemble small chicken drumsticks and, sometimes, the backs, and they are usually fried for consumption.

The American Bullfrog is also used as a specimen for dissection in many schools across the world.

External links

• Herps of Texas: Rana catesbeiana
• British Columbia Frog Watch Program: Bull Frog Fact Sheet
• Sonoran Desert Conservation Plan, Exotic Species: Bull Frog

References

ISBN links support NWE through referral fees

• Santos-Barrera, G. et al. 2004. [1]. 2006 IUCN Red List of Threatened Species., World Conservation Union. Retrieved on 12 May 2006. Database entry includes a range map and justification for why this species is of least concern.

,

previously Rana catesbeiana)

• Grzimek, B., D. G. Kleiman, V. Geist, and M. C. McDade. Grzimek's Animal Life Encyclopedia. Detroit: Thomson-Gale, 2004. ISBN 0307394913

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