Giant African Bullfrog, Pyxicephalus adspersus
Photos taken at Pretoria in December 2010
We had days of heavy rains,
and it resulted in a visit from a wonderfully impressive fellow!
That’s my son and grandson kissing the bullfrog,
NOT to be recommended,
very silly daddy, these frogs can bite really, really badly!
But he was a sweet old thing.
They had a 15 minute visit and it was back to where we found him.
Gaz is fascinated with frogs and toads, indeed all live things, and is always bringing them in to show us. We allow him to do so, encouraging his interest, and educating him about them at the same time. However, he knows that though they may be brought in, it is only to watch for some minutes. Then they have to be returned to where they came from, to allow them to return to their lives.
These are the Granddaddies of all frogs! I am not afraid of these creatures, but I prefer not to touch them. They are enormous and soft and bulbous and wet and I don’t find these particular ones ‘pretty’.
Description & Life History
The Giant African Bullfrog, Pyxicephalus adspersus, is the second largest frog in the world, the largest being the Goliath Frog, Conraua goliath. Vendors in the pet trade often use distortions of the African Bullfrog’s scientific name, such as “pixie frog” and “pyxie”, to refer to the young froglets that often surprise new pet owners by growing into monsters. Adult males can weigh well over a kilo (over 2.2 lbs) and males typically reach a snout-to-vent length of 17.5 cm (7 inches); specimens over 20 cm (8 inches) have been recorded (Passmore and Carruthers).
Females rarely exceed 12.5 cm (5 inches). Most anurans exhibit sexual dimorphism in size, generally the female being larger than the male. The African Bullfrog exhibits extreme size differences between the sexes, but the male is the larger animal. Males also have more powerful limbs and larger skulls. In the wild, some larger male African Bullfrogs in a population will demonstrate parental care by guarding their tadpoles against predators and, when necessary, insuring sufficient water is accessible to their brood by digging channels between pools (Balinsky and Balinsky; Kok and Du Preez; Cook, Ferguson and Telford). These guardian males have been known to attack animals much larger than themselves in defense of their offspring.
The size differences between the sexes are probably due to this parental behavior and the violent fighting that occurs between males at breeding time. Fighting takes the form of grasping an opponent in an attempt to flip or throw him (Passmore and Carruthers). These frogs are equipped with bony tooth-like projections called odontoids, located in the center of the lower jaw, which can deliver a very painful and bloody bite to an opponent or the finger of a human being. When forced on the defensive, these frogs will puff up with air to appear as large as they can, and in the case of guardian males they will lunge at the attacker with jaws open in an attempt to deliver a discouraging bite.
Adult frogs are generally green to dark green above, and pale cream or white below, with grayish blotches/spots. The pupils are horizontal, and while the fingers lack webbing, the toes have fleshy webbing. Both sexes have deep orange markings where the limbs meet the body.
Males tend to have a large amount of yellow coloration along the flanks and sometimes onto the throat; females have little yellow coloration beyond the base of the limbs. This bright coloration on males appears to play a display role during breeding (Channing, Du Preez and Passmore).
Adult males have proportionally larger heads, particularly where the head meets the body.
Sexing of these frogs is most difficult before their gonads develop but sex differences are usually quite apparent by a length of 10 cm (4 inches). Both sexes may grunt or force air through their airways to produce a dull hiss when grasped around the midriff, but females do not call.
Metamorphs are distinctly different in appearance to adults (so much so that lay men frequently don’t realize they are the same species). Metamorph froglets have black and various shades of green on their body, and three lines of bright green color, one running along the back from the nose to the vent, and one on either side of the body from the nose to the eye and from the eye along the side. These lines fade with age and this fading varies from individual to individual.
In countries where these frogs live, like South Africa, the climate is dry for much of the year. In Gauteng, South Africa, certainly the origin of most of the scientific studies of this species, the winter months of June, July and August see virtually no rain and temperatures are relatively cool (average temperatures for these 3 months: 5-17 °C/41-63 °F) (South African Weather Service). Significant rains are generally confined to the period of September to January and these wetter times correspond to the above ground activity of these frogs.
African Bullfrogs can spend as much as 10 months of the year aestivating to conserve water and to wait out conditions of drought and extreme temperatures. This aestivation involves burrowing into soft earth using the frog’s massive, flanged inner metatarsal tubercle (a projection found on each rear foot). When buried, the frog sheds many layers of skin which harden into a paper-like cocoon with only the frog’s nostrils exposed. The frog enters into a state of low metabolic activity and water retention.
Emergence is triggered by the first significant rains of summer, and breeding begins during the first daylight following the rains (if the rains occur at night, otherwise breeding activity is immediate). African bullfrogs are largely diurnal and this also applies to their breeding behavior. Adults congregate in ponds where the males call with a low, 1 second long whoop that resonates in the region of 100-300 Hz, sometimes likened to the sound of a cow. The call isn’t very loud and it doesn’t carry far. Males form groups; males fight and larger males may exclude the smaller males from the center of the group. Males assert dominance over others by lunging at, chasing and/or throwing their opponents, and the bites from these attacks can result in the death of smaller males and the loss of eyes. Females remain outside the group of males, at a distance, and when ready to breed they dive under the perimeter males to reach the central males. Amplexus, the grasping of the female behind the forearms by the male, occurs and the pair will spawn within a few hours in water approximately 7.5 cm (3 inches) deep. When ready to spawn, the pair lifts their hindquarters clear of the water and the female stimulates the male with her legs to trigger his release of sperm over her eggs. These are produced in midair and spread around the hindquarters to distribute the sperm, after which the eggs fall into the water. A total of 1600-4000 eggs are laid. The female signals her dismissal of the male by a prolonged arching of the back or by a tonic stretching of her body, whereupon the male releases his grasp and the pair separates. The male will attempt to breed with other females if possible but at this point the spawned female’s role ends.
After the flurry of breeding ends, many males and all females leave the spawning area. Larger dominant males may remain with their eggs (it is not clear if all of the eggs they guard are their own, though it seems unlikely). The tadpoles hatch within 48 hours at about 29 °C (84 °F) (van Wyk and Kok) and they have been observed to form a swarm/school around the guardian male (if he is present) 24 hours later. The tadpoles are omnivorous and detritivorous (cf. the Horned Frogs/Pacman Frogs, Ceratophrys, of South America, whose tadpoles are carnivorous but whose adults are very similar in behavior and habit to African Bullfrogs). The male will guard the tadpoles against predation, and males may be killed by predators in the process of defending their tadpoles. It was once thought that males may also eat some of their tadpoles, but this seems unlikely. Tadpoles may reach a total length of 6.4 cm (2.5 inches) at metamorphosis, and this can occur in as little as 17 days at 29 °C (84 °F). Pre-metamorphic tadpoles already exhibit the dorsal ridges of metamorphosed frogs. Metamorph froglet size is in the region of 2.2-3.6 cm (0.87-1.4 inches).
Metamorphosis is followed by rapid growth because these frogs must build reserves in preparation for the next drought.
Natural Range & Habitat
Pyxicephalus adspersus is recorded in much of sub-Saharan Africa. Many records exist from before the splitting of P. adspersus and P. edulis (Dwarf or Lowveld African Bullfrog). The map below is based on data from before the split and it is likely not 100% accurate. Some sources list Nigeria as part of the species’ natural range but this seems highly unlikely. It is interesting to note that this species ranges from temperate (the very southern extent of its range in South Africa), through sub-tropical and into equatorial regions, and at its greatest dimension the range is about 3,000 miles; truly massive for any species. Most of the published studies of P. adspersus have been carried out in South Africa, and this has implications: it is unlikely that the species’ behavior is the same across the entire range given the difference in climates.
The habitat of this species is the dryer savanna of southern Africa. Frogs typically live in and around large pans that fill with water after rains and frogs can be found in the surrounding bush land while moisture persists in the area.
With the appearance of so many variations of this frog which are obviously not the stereotypical Giant African Bullfrog (many do not grow larger than Lowveld African Bullfrogs, and colours vary greatly), it has become more and more apparent that the genus Pyxicephalus requires considerable attention from taxonomy scientists. It is a safe bet that what we refer to as the Giant African Bullfrog is largely confined to South Africa and neighboring countries.
African Bullfrogs are voracious eaters. The size of their mouth, their powerful jaws and the damage they can inflict with their odontoids mean that almost any animal that will fit in their mouths is a potential menu item. Dangling a finger in front of a frog’s head is not a great idea; these frogs can deliver very painful and deep bites that bleed copiously.
Silkworms & Hornworms:
PhoenixWorms (Soldier fly larvae):
Mealworms & Superworms: relatively high in fat and they have a particularly bad calcium: phosphorous ratio. Shouldn’t be used as a staple.
Earthworms, Night crawlers, sometimes called Lobworms or Canadian Earthworms are the large earthworm, Lumbricus terrestris
Mice & Rats:
Birds: chicks/chickens and quail.