AskDefine | Define bullfrog

Dictionary Definition

bullfrog n : largest North American frog; highly aquatic with a deep-pitched voice [syn: Rana catesbeiana]

User Contributed Dictionary



  1. Any of various large frogs of genus Rana, that have a deep croak and are native to North America.


large frog

Extensive Definition

The American Bullfrog (Rana catesbeiana,) is an aquatic frog, a member of the family Ranidae, or "true frogs", native to much of North America.


The bullfrog is a large species in the family Ranidae; it can grow to a length of 20 cm (7.87 inches) with a weight of up to 750 g (1.65 pound), the largest frog in North America. Females are typically larger than males. They are generally varying shades of green 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 frog has no scapula and a suprascapula which allows for greater range of motion for long jumps. The radius and ulna have become fused into a single bone, the radio-ulna, and the tibia and fibula have become fused into a single bone, the tibio-fibula. The vertebrae comprise 6 bones; nine are true vertebrae, and the rod-shaped urostyle that is almost as long as the other nine. 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.

Ecology and behavior

The American Bullfrog uses its skin, buccal cavity, and lungs for respiration. Cutaneous ("skin") gas exchange is very important in all amphibians. They 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 20,000 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. Premetamorphosis which is when the embryo genesis and growth and development occur, during this time the thyroid gland is absent.
  2. Prometamorphosis 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.


Bullfrogs will eat various types of animals, such as, insects, fish, snakes, birds and occasionally other frogs. Bullfrogs' hunting style is "sit and wait"; they will sit and wait for their prey to pass by, and then in a flash, will grab it with their tongue and eat it.


The American Bullfrog is native to North America. They are found in the United States, Canada and Mexico, east of the Rocky Mountains, but have been introduced to many other localities throughout the world. 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.

Human use



  • Database entry includes a range map and justification for why this species is of least concern.
  • (2005): Phylogeny of the New World true frogs (Rana). Mol. Phylogenet. Evol. 34(2): 299–314. PDF fulltext.
  • (2007) Constraints in naming parts of the Tree of Life. Mol. Phylogenet. Evol. 42: 331–338.
bullfrog in Danish: Amerikansk oksefrø
bullfrog in German: Amerikanischer Ochsenfrosch
bullfrog in Spanish: Rana catesbeiana
bullfrog in Esperanto: Taŭra rano
bullfrog in French: Ouaouaron
bullfrog in Italian: Lithobates catesbeianus
bullfrog in Hungarian: Ökörbéka
bullfrog in Dutch: Brulkikker
bullfrog in Japanese: ウシガエル
bullfrog in Norwegian: Amerikansk oksefrosk
bullfrog in Polish: Żaba rycząca
bullfrog in Portuguese: Rana catesbeiana
bullfrog in Simple English: Bullfrog
bullfrog in Finnish: Härkäsammakko
bullfrog in Swedish: Oxgroda
bullfrog in Thai: กบบูลฟร็อก
bullfrog in Ukrainian: Велика зелена жаба
bullfrog in Chinese: 美国牛蛙
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