American Bullfrog
  (Rana catesbelana)

Home

Bullfrog

Cane Toad

Carribean Frogs

Poison-Dart Frog

Wrinkled Frog

Picture of an american bullfrogTo hear a bullfrog, click here; sound was produced by Professor Mac F. Given; used with permission  





Citation for image:  photo taken by James Harding; used with permission 
Physical Description
  • Usually olive to brownish-green with mottled patterns of green and brown on their dorsal side; whitish, mottled with gray on belly; characteristic external ear fold (tympanum). 
  • Largest of true frogs usually 10-20 cm (4-8 inches); hind feet are webbed with enormous legs that make them great jumpers 
Feeding Behavior
  • Voracious opportunistic predators of aquatic, terrestrial and flying invertebrates and vertebrates, including birds and other amphibians; they threaten Hawai'i's unique marine animals, insects and spiders; eats almost anything it can overpower and swallow whole (can be cannibalistic)
  • Active both day and night but prefer warm, moist weather
  • Tadpoles' diet consists mainly of algae, plants and some invertebrate
Why and When Introduced to Hawai'i
  • One of the widest ranging species; native habitat is Canada, Mexico and eastern US but distributed widely
  • Introduced to the Big Island from Northern California in the late 1800's as a food source (click for fried frog legs) and insect eater
  • Now found on all Main Islands
Life cycle
  • Males are highly territorial with polygynous mating system
  • Females choose male territory and deposit eggs in water; males fertilize eggs externally; jelly coated eggs form large floating rafts containing as many as 40,000 eggs that need no adult attention; can produce multiple clutches in a year
  • Tadpoles appear 4 days after fertilization; slow development (1-3 years) of tadpoles which remain in ponds until undergo metamorphosis to form adult frogs; reach sexual maturity 2 years later
  • Adult bullfrogs are mostly aquatic
  • In wild, average lifespan is 7-9 years; in captivity, record is 16 years
Environmental Impact to Hawai'i
Globally, bullfrogs are listed as amphibians of least concern for endangerment because of their wide distribu- tion, tolerance to a broad range of habitats and great egg laying ability. In their native habitat, predators such as large water snakes, alligators, and snapping turtles keep frogs in check and fish eat their eggs. Historically, bullfrogs were hunted for their legs and in those states where they are considered as game animals, this may be a major method of controlling over- population.  Today, the bullfrogs in their
native habitat may be declining due to water pollution, pesticide contamination and over- harvesting.

However, bullfrogs are recognized as an invasive species when found in their non-native environment because their predators are rare. For example, fish in non-native regions avoid bullfrog eggs and tadpoles because of their undesirable tastes whereas fish in native habitats have acquired a taste for them. Their powerful jumping legs allow them to hop between small ponds, and in Hawai'i,
they survive in brackish
water. In Western states where they threaten native birds, hunting adults, collecting egg masses, constructing frog-proof fences  around ponds and trapping young juveniles as they leave ponds have met with some success.

Casper and Hendricks have concluded that bullfrogs in their native habitat should be conserved. In Hawai'i, elimination and control measures should be practiced as they most likely have affected the native insect and bird species.