American bullfrog, Rana catesbeiana, often simply known as the bullfrog
in Canada and the United States, is an aquatic frog, a member of
the family Ranidae, or true frogs, native to much of
North America.This is a frog of larger, permanent water bodies,
swamps, ponds, and lakes, where it is usually found along the water's
edge.On rainy nights, bullfrogs, along with many other amphibians,
travel overland, and may be seen in numbers on country roads.
bullfrogs live longer in warm weather. They have been widely introduced
across North America (see range map). The original, naturally determined
range did not include the far western regions where it is found
Bullfrogs grow on average to be about 3.5 to 6.0 inches (915
cm) in body length (although there are records of some up to 8.0
inches), legs add another 710 inches (1725 cm) to length.
The adult bullfrog skeleton is representative of tetrapod vertebrates,
comprising an axial skeleton (skull and vertebrae) and an appendicular
skeleton (pectoral girdle and forelimbs, pelvic girdle and hindlimbs).
Ranids, however, lack ribs. The pronounced pair of dorsal humps
in the back of ranid frogs are the ends of the pelvic ilia, homologues
of the human hips.
bullfrog skull is highly fenestrated. The orbits open ventrally
through the roof of the mouth to accommodate eye retraction during
locomotion and swallowing. The skull bears a continuous row of tiny
teeth on the maxilla and premaxilla and a pair of small vomerine
teeth on the palate. The mandible is toothless.
bullfrog nervous system consists of a brain, spinal cord, and peripheral
nerves, including cranial, spinal, and sympathetic nerves serving
organs, such as the heart, gastrointestinal tract, kidneys, and
have eardrums (tympana) the same size as their eyes. Males' eardrums
Ranid frogs absorb oxygen and eliminate carbon dioxide through their
moist skin, the lining of the mouth, and the lungs. When in the
air, as opposed to underwater, frogs continuously elevate and lower
the floor of the mouth, which serves to ventilate the mouth, or
buccal cavity, and exchange gases through the richly vascularized
lining of the mouth. Periodically, the regular rhythmic pumping
of the floor of the mouth is interrupted by a deeper lowering of
the throat, at the extreme of which, the glottis opens and the throat
muscles contract vigorously to force air from the mouth into the
lungsthe nostrils are closed off. This lung ventilation may
be performed several times, after which the shallow buccal ventilation
resumes. Lacking ribs, frogs must supply the pressure to force air
into their lungs, whereas mammals can enlarge the cavity surrounded
by the rigid rib cage and allow the atmosphere to supply the pressure.
Fertilization is external in ranid frogs. In the mating grasp, or
amplexus, the male rides on top of the female, grasping her with
his forelimbs posterior to her forelimbs. The female bullfrog deposits
her eggs in the water and the male simultaneously releases sperm.
begins in late spring or early summer. Males defend and call from
territories, attracting females into a territory to mate. The call
is reminiscent of the roar of a bull, hence the frog's common name.
A female may produce up to 20,000 eggs in one clutch.
Eggs hatch in three to five days. Time to metamorphosis ranges from
a few months in the southern to three years in the northern parts
of the geographic range. Maximum lifespan in the wild is estimated
at eight to 10 years, but one captive lived almost 16 years.
Stomach content studies going back to 1913 suggest the bullfrog
preys on any animal it can overpower and stuff down its throat.
Bullfrog stomachs have been found to contain rodents, small turtles,
snakes, frogs (including bullfrogs), birds, and a bat, as well as
the many invertebrates, such as insects, which are the usual food
of ranid frogs. These studies furthermore reveal the bullfrog's
diet to be unique among North American Rana in the inclusion of
large percentages of aquatic animals, e.g., fish, tadpoles, planorbid
snails, and dytiscid beetles. The specialized ability of bullfrogs
to capture submerged and large, strong prey comprises a pronounced
biting motor pattern that follows up on the initial and typical
ranid tongue strike. Adaptation to target image displacement
due to light refraction at the water-air interface consists of the
bullfrog's application of tongue surface comparatively posterior
to the perceived location of the prey target. The comparative ability
of bullfrogs to capture submerged prey, compared to that of the
green frog, leopard frog, and wood frog (R. clamitans, R. pipiens,
R. sylvatica, respectively) was also demonstrated in laboratory
motion elicits feeding behavior. First, if necessary, the frog performs
a single, orienting bodily rotation ending with the frog aimed towards
the prey, followed by approaching leaps, if necessary. Once within
striking distance, the bullfrog emits its feeding strike, which
consists of a ballistic lunge (eyes closed as during all leaps)
that ends with the mouth opening, extension of the fleshy and mucous-coated
tongue upon the prey, often engulfing it, while the jaws continue
their forward travel to close (bite) in close proximity to the prey's
original location, just as the tongue is retracted back into the
mouth, prey attached. Large prey that do not travel entirely into
the mouth are literally stuffed in with the forearms. In laboratory
observations, bullfrogs taking mice usually dove underwater with
prey in mouth, apparently with the advantageous result of altering
the mouse's defense from counterattack to struggling for air. The
tiny teeth of bullfrogs are useful only in grasping. Asphyxiation
is the most likely cause of death of endothermic (warm-blooded)
While occasionally kept as pets, the American bullfrog provides
a 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 shone
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. In some states,
breaking the skin while catching them is illegal, and either grasping
gigs or hand capture are used. The only parts eaten are the rear
legs, which resemble small chicken drumsticks and, sometimes, the
backs, which are usually fried.
American bullfrog is also used as a specimen for dissection in many
schools across the world.
American bullfrog is the state amphibian of Iowa, Missouri, and
American bullfrog has been introduced to many countries in the world,
such as South Korea, Western Europe, Brazil, Colombia and Australia,
where it has become a nuisance to those countries' natural ecology
because of its appetite.
American bullfrog has been widely introduced to most western states,
and is now very common there, especially in California, and poses
a serious threat to native species, such as the California red-legged
frog because bullfrogs are aggressive and will eat anything smaller
than themselves. They are considered a factor of the red-legged